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THE AMAZING WORLD OF SALAMANDERS

The views expressed are those of the author and are not necessarily those of Scientific American.


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The salamanders are here. Clockwise from top left: Chinese giant salamander (Andrias davidianus), Jefferson salamander (Ambystoma jeffersonianum), Blue-spotted salamander (A. laterale), Eastern newt (Notophthalmus viridescens). Andrias photo by Markus Bühler, remainder by Rosemary Mosco, used with permission.

Tet Zoo loves amphibians* (that’s anurans, salamanders, caecilians and their close relatives), and since 2008 I’ve been making a concerted effort to get through all the amphibian groups of the world. I’ve failed, and I’m blaming that entirely on the fact that I can’t put the time I need to into blogging. Sigh, always busy spending my time working my backside off for stupid money, sigh… Anyway, back in 2008 I did succeed in producing a couple of articles that review the caudates – the salamanders – of the world.

* I have to say at this point that I really prefer to use the term lissamphibian when referring to extant amphibian lineages. Mostly, this is because I somewhat dislike the use of the term ‘amphibian’: its perpetuation makes people think that non-amniote tetrapods – or anamniotes – are all close relatives, all closely related or ancestral to lissamphibians. However, since the term amphibian is in such wide use and is overwhelmingly popular among biologists and conservationists, I’ll stick with it here. Oh, and no, we haven’t forgotten you, albanerpetontids (round these parts, they’re affectionately known as albies).

Sadly, there aren't that many salamander-themed books to track down and obtain: here's an (admittedly Eurocentric) collection of volumes from the TetZoo Library.

There are about 655 recognised living salamander species, and many aspects of their diversity, biology and behaviour are fascinating. There are (or were) giant salamanders more than 2 m long, tiny, tree-climbing salamanders with prehensile tails, partially herbivorous salamanders that possess beaks, cave-dwelling salamanders, long-bodied, aquatic eel-like salamanders, and armoured salamanders with defensive spikes. Claws, intra-uterine cannibalism, neoteny, the defensive shedding of tails and limbs, weird developmental shifts in digital development, bizarre warning displays, lekking and nuptial dancing, facultative herbivory and fungivory, dedicated cave-dwelling… it’s all here. So shame on you if the thought ever occurred to you that salamanders might be plain or boring. A lot of new stuff on these animals has appeared since 2008, meaning that I’ve had to substantially update my original text. Without further ado, let’s get on with it…

Mudpuppy (Necturus maculosus), one of many salamanders that retains external gills and a fully aquatic lifestyle into adulthood. More on mudpuppies below. Photo by Matt Keevil, used with permission.

The term caudate means ‘possessing a tail’ and, in contrast to anurans and caecilians, salamanders retain the body shape that seems to have been plesiomorphic for amphibians. Having said that, even salamanders exhibit a list of anatomical specialisations that make them unusual compared to other tetrapods: they’ve lost a long list of skull bones that are present in other anamniotes (including the postorbitals, jugals, tabular, supraoccipital and ectopterygoids), and also lack a middle ear (though they’re not deaf). Bizarrely, salamanders have disproportionately large amounts of DNA.

Salamanders are generally Laurasian and the groups that occur on the southern continents (there are plethodontids in South America and some salamandrids in northern Africa) have only gotten there comparatively recently. An important theme which has cropped up several times independently within different salamander clades is neoteny: the retention of juvenile characters into sexual maturity. It’s been widely suspected that neoteny results in the retention of confusing plesiomorphic characters, and in extensive convergence, so working out the relationships of neotenous salamander clades has been difficult (Wiens et al. 2005). Phylogenetic studies on salamanders have in fact differed pretty radically in the relationships they infer (particularly with respect to the position of sirens), though a rough consensus has emerged.

The oldest salamanders

Skeleton of Karaurus sharovi (total length 20 cm). Image by Davide Meloni, licensed under Creative Commons Attribution-Share Alike 2.0 Generic license.

The oldest salamanders we know of are Middle Jurassic forms from central Asia (Kokartus honorarius) and England (two species of Marmorerpeton). What we know indicates that these early forms looked superficially like stout-bodied living ones, but they lacked various bony and muscular characters present in the crown-group. The best known early salamander – Karaurus sharovi from the Upper Jurassic of Kazakhstan – has been compared to living mole salamanders (ambystomatids) and perhaps lived in a similar manner (Estes 1981). [Adjacent image by David Meloni.]

Whether the name Urodela is restricted to the crown-group, with Caudata used for the total-group, or whether the name Caudata is restricted to the crown-group, with Urodela used for the total-group, depends on which authors you pay attention to. Evans & Milner (1996) argued that it makes better sense to use Caudata for the total-group, and this seems to have been mostly followed and is used here. So Marmorerpeton and the karaurids Kokartus and Karaurus are stem-caudates but not urodeles. A few other Mesozoic taxa, like Pangerpeton and Jeholotriton from the Jurassic or Cretaceous of Liaoning Province in China, are regarded by some authors as additional stem-caudates (Wang & Evans 2006). [Image below by internet hero Nobu Tamura.]

Life reconstruction of a swimming Chunerpeton, by Nobu Tamura. Licensed under Creative Commons Attribution 3.0 Unported license.

Various fossil salamanders from the Middle and Upper Jurassic seem to be crown-group salamanders: that is, early members of the lineages that include the cryptobranchids (giant salamanders) or hynobiids (Asian salamanders) (together, cryptobranchids and hynobiids are termed cryptobranchoids), or members of Salamandroidea, the ‘advanced’, internally fertilising salamander clade. Chunerpeton from the Daohugou Beds of Inner Mongolia (Gao & Shubin 2003, Carroll & Zheng 2012), and – according to Carroll & Zheng (2012) – Pangerpeton, Jeholotriton, Regalerpeton, Liaoxitriton and Iridotriton are all Mesozoic cryptobranchoids. If this is correct, and if there’s a sister-group relationship between cryptobranchoids and salamandroids, then members of both of these major salamander clades had appeared before the end of the Jurassic. The recent description of Beiyanerpeton jianpingensis from the Jurassic Tiaojishan Formation (Gao & Shubin 2012) seems to confirm the predicted presence of salamandroids in the Jurassic. Iridotriton hechti from the Morrison Formation has also been interpreted as an early salamandroid (Evans et al. 2005) but this was contested by Gao & Shubin (2012) who found it to be a cryptobranchoid. By the Upper Cretaceous, members of most or all of the living salamander ‘families’ had probably appeared.

Cryptobranchoids: giant salamanders and Asiatic salamanders

I'm not gonna lie to you: some hynobiids look a bit boring. This is a Fischer's clawed salamander (Onychodactylus fischeri). Image by Pierre Fidenci, licensed under Creative Commons Attribution-Share Alike 2.5 Generic license.

Two particularly ancient groups of salamanders are still around today: the hynobiids and the cryptobranchids. Hynobiids, generally just called Asiatic salamanders, are a poorly known group of about 50 species that occur from Afghanistan and Iran eastwards to Japan, though between the Miocene and Pleistocene they also occurred in Europe (Venczel 1999). Some hynobiids occur in cold parts of northern Asia and are particularly cold-tolerant, being able to withstand freezing at temperatures below -50°C for months at a time (that is, they literally get frozen alive and can stay dormant in a block of ice). [Image of Onychodactylus above by Pierre Fidenci.]

Some hynobiids employ aquatic suction feeding while others have a projectile tongue. Some (like Onychodactylus) have evolved claw-like structures on their digit tips. A recent study of hynobiid phylogeny and biogeography indicated that the group originated in China, with the rest of its history and distribution being strongly influenced by local events like the desertification of Mongolia and the uplift of the Tibetan plateau (Zhang et al. 2006).

One of many photos I have of captive Asian giant salamanders. It's not the best photo in the world, but at least it shows the animal in an interesting pose. Photo by Darren Naish.

Grouped with hynobiids in the clade Cryptobranchoidea (or Cryptobranchiformes), are the giant salamanders, or cryptobranchids. There are only three extant species (the North American Hellbender Cryptobranchus alleganiensis, the Chinese giant salamander Andrias davidianus and Japanese giant salamander A. japonicus); all are salamanders of fast-flowing, well-oxygenated water (but this wasn’t the case for all fossil species). All possess dorsoventrally flattened bodies. Gills are absent in the adults and their lungs apparently don’t function in respiration, so all gas exchange occurs across the extensively folded, wrinkled skin. Eyelids are absent (a sure sign of aquatic habits in a caudate).

Giant salamanders are famous for, well, being giant, with record-holding specimens of the Chinese giant salamander reaching 1.8 m and 65 kg. Some fossil species were bigger, with A. matthewi from Miocene North America reaching 2.3 m. Little known is that cryptobranchids have particularly vicious teeth, exude a foul smell which has been partially likened to “the rankest public urinal crossed with that of stale sweat” (Brazil 1997, p. 64), and that the males brood the eggs. Giant salamanders can inflict massive wounds with their teeth: during territorial fights males frequently sever digits, limbs, and bits of tails of rivals, and massive fatal slices across the neck – sometimes resulting in decapitation – are apparently not uncommon.

Asiatic giant salamanders have complex social lives. Big 'den-master' males fight for supremacy and guard special breeding burrows. Cartoon by Darren Naish.

Chunerpeton from the Jurassic of China (mentioned above) has been identified as a cryptobranchid, in which case both this group and its sister-taxon Hynobiidae have been around for a long time. Chunerpeton seems to have been reasonably large – about 200 mm long – but, of course, not ‘large’ by comparison with the Cenozoic species. For much more on those species see the Tet Zoo article on giant salamanders (link below).

Of batrachosauroidids and scapherpetontids (…. or scapherpetids)

At top, life reconstruction of Batrachosauroides dissimulans, a big, aquatic salamander that probably looked amphiuma-like. Below: skull of the same species. Illustrations by Darren Naish.

Having discussed cryptobranchoids, I should say that there are a couple of entirely fossil salamander groups – naming Batrachosauroididae and Scapherpetontidae* – that have sometimes been regarded as part of this clade (Estes 1969). However, Estes (1981) later classified batrachosauroidids with proteids (olms and mudpuppies) and scapherpetids with ambystomatids. Batrachosauroidids have a fossil record that extends from the Upper Cretaceous to the Pliocene (a possible member of the groups has been reported from the Jurassic-Cretaceous boundary, however) and they’re known from North America as well as Germany and France. They seem to have been large, long-bodied salamanders, probably with reduced limbs, with subtriangular, poorly ossified skulls superficially similar to those of amphiumas. Long ‘stalks’ on the occipital condyles suggest an ability to elevate the cranium extensively and hence open the jaws wide. Large size is indicated by the known skull and jaw remains: Batrachosauroides and Opisthotriton both have skulls about 30 mm long, which isn’t bad for a salamander.

* David Marjanović reminds me (see comments) that it should really be Scapherpetidae.

Scapherpetids are known from the Upper Cretaceous, Paleocene and Eocene and they’re mostly known from fragments (vertebrae and partial mandibles). They must have been large (vertebral centra are usually something like 20 mm long), and the shapes of their vertebrae and limbs show that they were another long-bodied, limb-reduced, mostly aquatic group: in Scapherpeton from the Upper Cretaceous, the limb bones are small compared to the size of the vertebrae, the proportions seemingly being about intermediate between Dicamptodon and amphiumas (Estes 1981).

The amazing sirens

Captive Lesser siren (Siren intermedia), one of three extant siren species. Photo by Stan Shebs, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

Sirens (Sirenidae) are perhaps the strangest of salamanders. Indeed, they’re so strange that at times they’ve even been excluded from Caudata and put on their own as a ‘new’ sort of amphibian group termed Trachystomata or Meantes. Superficially eel-like, neotenic, and lacking a pelvis and hindlimbs, they possess external gills, lack eyelids, are adept at burrowing in mud, and reach 95 cm in the largest species [Image above by Stan Shebs]. The Cretaceous-Paleocene siren Habrosaurus reached 1.6 m, which is enormous and frightening. Habrosaurus, in fact, is so spectacular that I was half-expecting there to be some life restorations of it online (there are two species: H. prodilatus from the Campanian of Alberta, and H. dilatus from the Maastrichtian and Paleocene of Wyoming and Montana). Alas, that doesn’t seem to be the case, so I had to resort to creating this…

A scene from Late Cretaceous North America: a drinking tyrannosaur darts away in surprise as a panicking Habrosaurus bursts from the edge of shallow water in a flurry of spray. The habrosaur (a Cretaceous siren) is a big individual, 1.6 m long. Illustration by Darren Naish.

The big surprise is that sirens have a horny beak and pavements of teeth on the palate. The beak forms a broad platform inside the jaws, and the jaw joint is ventrally displaced relative to the rest of the skull. All of these features are adaptations for crushing, and field studies show that (as you might predict) sirens feed extensively on gastropods and bivalves. Sirens are unlike most salamanders in that their teeth are (usually) not pedicellate: that is, their teeth are not connected to the jaw bones by way of a flexible pedicle. Salamanders start their life as larvae without pedicellate teeth and normally develop the condition as they mature, so lack of pedicelly is seen as a neotenous condition. Proteids also lack pedicellate teeth as adults, as do batrachosauroidids and the Jurassic salamanders Kokartus and Beiyanerpeton. The fact that certain early salamanders (including stem members of the group) lack pedicellate teeth seems to challenge the hypothesis that pedicelly is a synapomorphy of Lissamphia and a primitive, inherited character for salamanders (Gao & Shubin 2012).

Sirens also appear to be partially herbivorous, ingesting vascular plants and algae. They have enlarged hindguts that may house symbiotic microbes (Pryor et al. 2006). If this is correct it’s a big deal and would make them unique among caudates. They are also unusual in that they can survive desiccation by forming a sort of mucus cocoon in the mud, a habit very similar to that better known for lungfishes. Oh yeah, and they emit a yelping noise when grabbed (Halliday & Verrell 1986).

A phylogenetic hypothesis for salamanders, based predominantly on Pyron & Wiens (2011) but with some of the clade names coming from Frost et al. (2006). Hynobiid by Pierre Fidenci (CC Attribution-Share Alike 2.5 Generic license), sirenid by Stan Shebs (CC Attribution-Share Alike 3.0 Unported license), salamandrid by Markus Bühler, dicamptodontid by Jeffrey-Marsten, and plethodontid and ambystomatid by Rosemary Mosco.

Several features support the view that cryptobranchoids are anatomically primitive relative to the other crown-group salamanders, the salamandroids. Cryptobranchoids still possess an angular bone in the lower jaw, and they also practise external fertilization. Some studies indicate that cryptobranchoids are not alone in being outside of Salamandroidea, since it’s been argued that sirens belong here too (Larson & Dimmick 1993, Wiens et al. 2005, Pyron & Wiens 2011).

In a radical departure from this view, Frost et al. (2006) found sirens to be nested well inside Salamandroidea, being especially close to proteids (mudpuppies and olms). They used the name Perennibranchia Latreille, 1825 for this proposed siren + proteid clade. A position within Salamandroidea for sirens would be very surprising since sirens don’t possess any of the reproductive characters otherwise typical for this group, including internal fertilization, the possession of spermathecae or the production of spermatophores (read on for more on all of these features). If Frost et al. (2006) are correct, some pretty radical reversals have occurred in siren evolution. The hypothesis that sirens are not members of Salamandroidea, then, appears more parsimonious on face value.

Noterpetontids are mostly represented by vertebrae, like these Noterpeton specimens from the Upper Cretaceous of Bolivia (from Gayet et al. 2001).

Sirens have a fossil record extending back to the Upper Cretaceous, and while the extant species are all North American, fossil representatives have been described from Sudan, Germany, India and Bolivia. Given that salamanders are, as we’ve seen, mostly Northern Hemisphere animals, the presence of these animals in Gondwanan locations is significant. The identification of these fossils – some of which have often been united in a group termed Noterpetontidae – as sirenids has been challenged (Gardner 2003). One possibility is that noterpetontids are stem-sirens (Marjanović & Laurin 2007).

The wonder that is the internally fertilizing salamander clade

Salamandroidea – also named Salamandriformes or Diadectosalamandroidei – is also known as the ‘internally fertilizing salamander’ (or IFS) clade (Larson & Dimmick 1993). This is the clade that contains the vast majority of salamander species and lineages, including the (mostly) American lungless salamanders or plethodontids, the chunky mole salamanders (or ambystomatids) of the Americas, and the (mostly) Eurasian salamandrids. While its roots are in the Mesozoic, Salamandroidea is mostly a Cenozoic clade that exploded in diversity during the late Paleogene and Neogene.

How are these salamanders capable of ‘internally fertilizing’ when males don’t have an intromittent organ? As all amphibian fans will know, they produce an elaborately shaped sperm package (the spermatophore) that they deposit on the substrate. It’s then picked up by the female’s cloaca (some salamanders do all of this on land, others on the floor of a pond or stream. Some species are, err, well stocked and can produce multiple spermatophores in fairly rapid succession).

Karpathos Lycian salamander (Lyciasalamandra helverseni), one of several Lyciasalamandra species named in recent decades (specifically, 1963). Note the tail spike! Photo by Benny Trapp, licensed under the Creative Commons Attribution 3.0 Unported license.

In order to get the female’s cloaca to make contact with the spermatophore, the male has to guide or place the female correctly, and salamanders have evolved all kinds of tricks to make sure this happens. Most remarkable (in my opinion) is the soft, dorsally projecting spike that some male salamandrids possess at the base of the tail. Once a female has expressed interest as a mating partner, the male manoeuvres himself to get beneath the female, and inserts the spike into her cloaca (Sever et al. 1997), presumably to get her into position for spermatophore collection.

Once a female has absorbed the spermatophore’s sperm-filled cap, she retains the sperm in special cloacal pockets called spermathecae, and it might be stored here for months or even years (by the way, at least one salamandrid breaks all the rules, and engages in cloacal contact during sperm transfer. What is it with evolution and its blatant disregard for rules and consistency?).

Super-weird amphiumas

Captive amphiuma. We tend to forget how amazing it is that salamanders have evolved giant, eel-like aquatic forms on at least two occasions. Photo by Darren Naish.

A moment ago, we looked at the bizarre sirens. Also long-bodied and super-weird are the amphiumas, or amphiumids. They’re represented by just three extant species in one genus (Amphiuma): all are restricted to the south-eastern USA, and fossil genera show that the group has been present in North America since the Upper Cretaceous at least (Gardner 2003).

Like sirens, amphiumas are eel-like, neotenic salamanders that lack eyelids, but unlike sirens they possess hindlimbs and don’t have external gills. They have rather long skulls with unusually textured bone in the facial region and, unlike sirens, practise internal fertilization. The alternative name ‘congo eel’ (often misunderstood as ‘conger eel’ by laypeople: the real conger eels really are, of course, eels) is particularly dumb, given that they aren’t eels and don’t come from the Congo or anywhere near it. Amphiumas are reportedly of unpleasant temperament and are said to bite savagely. [Photo below of amphiuma skull from Boneman_81's flickr site.]

Skull of Amphiuma tridactylum, photo by Boneman_81.

Surprisingly perhaps, amphiumas have been found to be the sister-group to the plethodontids (Wiens et al. 2005, Pyron & Wiens 2011), and both groups were allied in the newly named clade Xenosalamandroidei by Frost et al. (2006). Incidentally, Edward Cope thought that amphiumas were ancestral to caecilians.

Mudpuppies, waterdogs and olms

How could I not mention the Black Mudpuppy, the world's best parthenogenetic salamander superhero? The Black Mudpuppy is a comic, featuring nazi dinosaurs, Aztec gods and a whole world of awesome. Image kindly provided by Ethan Kocak.

Also aquatic and neotenic are the proteids: the mudpuppies, waterdogs and olms [adjacent image shows THE BLACK MUDPUPPY]. Like amphiumas, proteids practise internal fertilization and are definitely parts of the IFS clade. They have bushy external gills, laterally compressed tails and lack maxillae (sirens also have reduced maxillae). Only two extant genera are recognised – Necturus from North America (the mudpuppies and waterdogs) and Proteus from Europe (the olms). Fossil taxa extend the group’s history back to the Palaeocene (Estes 1981) [UPDATE: an Upper Cretaceous taxon - Paranecturus garbanii from the Hell Creek Formation - was published in 2013. See comments]. Proteid monophyly has been found to be questionable in some studies (Weisrock et al. 2005) but supportable in others (Trontelj & Goricki 2003, Wiens et al. 2005, Frost et al. 2006, Pyron & Wiens 2011).

An Olm (Proteus anguinus) of the far better known, pink, cave-dwelling form. Image by Arne Hodalič, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

Olms used to be regarded as uniquely cave-dwelling [adjacent image by Arne Hodalič], but we now know of a surface-dwelling form, the Black olm P. anguinus parkelj (olms have been covered on Tet Zoo before: see the links below). Proteids have been variously shuffled about the salamander family tree. Some studies have found them to be close relatives of sirens (Gao & Shubin 2001, Frost et al. 2006) whereas others find them to be the sister-group to the clade that includes amphiumas, lungless salamanders, mole salamanders and salamandrids (Pyron & Wiens 2011).

Axolotls and their friends and relatives

The 33-ish species of mole salamander, or ambystomatids, derive their name from their predominantly fossorial habits. These are robust-bodied North American salamanders, some of which – like the Tiger salamander Ambystoma tigrinum – are large (reaching 40 cm) and brightly coloured. Particularly well known is the fact that some, like the Axolotl A. mexicanum, are neotenous and aquatic. While the Axolotl is abundant as a pet and laboratory animal, the wild population – endemic to Mexico’s Lake Xochimilco – is in danger. Two mole salamander species are particularly odd in that they consist only of females. There are some detailed articles on ambystomatids in the Tet Zoo archives, see links below.

Coastal giant salamander (Dicamptodon tenebrosus). There are some amazing photos online showing dicamptodontids eating enormous banana slugs. Photo by Jeffrey-Marsten and in public domain.

The four species of Pacific giant salamander (‘giant’ = 30 cm) – all united in Dicamptodon – are included by some workers in Ambystomatidae, but are otherwise regarded as worthy of their own ‘family’, termed Dicamptodontidae. All Dicamptodon species have particularly solid-boned skulls and blade-like teeth and are voracious predators of smaller salamanders, rodents and small snakes. Surprisingly, they’re pretty good climbers and some have been seen clambering about in vegetation 2.4 m off the ground (Stebbins 1966).

Fossil dicamptodontids are known from the Palaeocene onwards (in fact Dicamptodon itself goes back this far), with a couple of taxa being European: Rocek (1994) said that these are dicamptodontids “beyond any doubt” (p. 53), but there is in fact now a substantial amount of doubt about the alleged dicamptodontid affinities of the taxa concerned. Incidentally, one of the European taxa is Bargmannia Herre, 1955, but by googling this name I’ve learnt that it’s preoccupied by the siphonophore Bargmannia Totton, 1954 (ha – one year!).

Rhyacotritonidae, named only for the semi-aquatic torrent salamanders Rhyacotriton from the north-western US and previously grouped with Dicamptodon, might instead be closer to amphiumas and/or plethodontids (Pyron & Wiens 2011). In contrast to most ambystomatids and dicamptodontids, torrent salamanders are small (total length 10 cm or less) and with poorly ossified skulls, wrists and ankles. They’re animals of cold mountain streams and seepages, often found in splash zones or wet mossy places.

The lungless salamanders

Green aneides or Green salamander (Aneides aeneus), definitely one of the most sinister looking of the plethodontids. But don't let that fool you, they're really ok. Or are they?... Aneides is a plethodontine, a close relative of Ensatina and the Korean plethodontid Karsenia. Image by Rosemary Mosco, used with permission.

Plethodontids – the mostly American lungless salamanders – are the most speciose (c. 380 species) and most diverse salamander group with aquatic, terrestrial, fossorial, cave-dwelling and even arboreal species. The smallest salamanders, those of the genus Thorius, belong to this group and may be adult at just 30 mm in total length (yes, including the tail… hence ‘total’ length). They lack lungs entirely, with all respiration occurring across the skin and membranes of the pharynx. Vertical grooves running the length of the body – the costal grooves – draw moisture up around the body, helping the skin remain moist. Phylogenetic studies show that plethodontids have done some freaky things in their evolution, with reversals and rampant convergence being well documented in some lineages.

A North American plethodontid montage. From top to bottom: Red salamander (Pseudotriton ruber), a spelerpine; Four-toed salamander (Hemidactylium scutatum), the only extant member of its lineage (and hence sometimes given its own ‘subfamily’, Hemidactylinae); and Northern dusky salamander (Desmognathus fuscus), one of many Desmognathus species within Plethodontinae. All images by Rosemary Mosco and used with kind permission.

Some plethodontids escape from predators by tucking in their limbs and rolling downhill, others have ballistic tongues or highly sensitive binocular vision. Plethodontids are not just really interesting; they have also proved really instructive in terms of what they’ve taught us about speciation, hybridisation, species concepts and how evolution works. Much of this research has been produced by University of California’s David B. Wake and his colleagues and students: his lab’s webpage (with many free pdfs) is here.

We saw above that some salamanders (the sirens) appear to be herbivores. Equally remarkable is the claim that some plethodontids are fungivores: if, that is, observations reported by Miller (1944) are correct. Miller wrote that the Santa Cruz black salamander Aneides flavipunctatus niger (recognised as a full species by some workers) ate the fruiting bodies of fungi, and it’s been suggested that other Aneides species might do likewise. However, there is some scepticism about this, and other salamander workers haven’t reported the same behaviour (to my knowledge).

Plethodontids are not uniquely American, as the European cave salamanders also belong to this group. Furthermore, a really amazing recent discovery is that this group also exists in Asia: to date, only one Asian species belonging to the group is known – the Korean crevice salamander Karsenia koreana Min et al., 2005 – but it’s possible and perhaps likely that additional Asian species await discovery. The plethodontid fossil record isn’t great, extending back to the Miocene in both North America and Europe.

Salamandrids: ribs as weapons, viviparity, sex aids

Ziegler's crocodile newt (Tylototriton ziegleri), one of many gnarly, badass-looking salamandrids. Image by Nguyen Thien Tao, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

To many people, the most familiar of salamanders are the salamandrids: the mostly North American-Eurasian group that includes the newts and the familiar Fire salamander Salamandra salamandra and its relatives (note that hyper-variable ‘S. salamandra‘ of tradition is a species complex containing at least six different species-level units). There are about 75 living salamandrid species. Most studies have found salamandrids to be close kin of mole salamanders (Larson & Dimmick 1993, Frost et al. 2006, Pyron & Wiens 2011) though others have allied them with plethodontids (Gao & Shubin 2001).

Everybody loves Salamandra salamandra. It's a robust, boldly pattern European salamandrid that can reach 28 cm in total (its close relative S. infraimmaculata can be a bit larger, reaching 32 cm). Photo by Markus Bühler.

Salamandrids have a fossil record that extends back to the Paleocene of Europe thanks to Koaliella from France and Germany: Zhang et al. (2008) posited the origin of the group as an Upper Cretaceous event. Numerous other fossil taxa are known from between the Middle Oligocene and Pleistocene (including Archaeotriton, Brachycormus, Chelotriton, Megalotriton, Oligosemia, Palaeopleurodeles and Carpathotriton). I always hoped that Megalotriton (which has sometimes been visualised as a giant version of the living Fire salamander) was 1 m long or more but… no. With vertebrae of – at most – 12.5 mm, it was perhaps as much as 40 cm long in total. Some phylogenetic studies find Salamandridae to consist of two major clades: Salamandrinae (containing Chioglossa, Lyciasalamandra, Mertensiella and Salamandra) and Pleurodelinae (containing all the others). [Newt images below by Neil Phillips of UK Wildlife.]

A European newt montage. At top: many newts are highly showy, males possessing soft frills, toe fringes and bold patterns. This is a male Smooth newt (Lissotriton vulgaris) in breeding dress. Middle: Smooth newt larva. While still aquatic and with external gills, the small size of the gills and well-developed limbs show that this individual is close to metamorphosis. Newt larvae are sometimes called ‘newtpoles’ but the correct term is ‘efts’. Bottom: all three British newts alongside one another. The massive size of the Great crested newt (Triturus cristatus) alongside L. vulgaris (spotted throat) and L. helveticus (white throat, paler, less spotted underside) is notable. All photos by Neil Phillips, used with permission.

The very distinctive Spectacled salamander Salamandrina terdigitata and Northern spectacled salamander S. perspicillata, both endemic to western Italy, are generally recovered as forming the sister-group to the salamandrine + pleurodeline clade (Zhang et al. 2008, Pyron & Wiens 2011). These unique salamandrids are proportionally long-tailed, only have four toes on the hindfeet, and display their bright red ventral tail surfaces by forming a vertical loop with the tail when disturbed.

Salamandrids are generally amphibious, terrestrial outside of the breeding season, and often with poisonous skin glands and brightly coloured undersides. Some species (most famously the North American Taricha newts) are among the most poisonous of amphibians, and some perform a special contorted display – called an unkenreflex – to show off the vivid reds, oranges or yellows they have on their bellies. This is the group that include the species with the soft, spike-shaped ‘sex aid’ mentioned above: it’s present in the salamandrine species originally grouped together in the genus Mertensiella (they were originally grouped together due specifically to the presence of this structure). However, the species concerned are now known not to be especially close relatives (one of them – Luschan’s salamander – is now the type species of the genus Lyciasalamandra), meaning that some authors have suggested the possibility that tail spikes of this sort were originally more widespread in salamandrines, and lost in various lineages, including in Salamandra (Veith & Steinfartz 2004).

Iberian ribbed newt (Pleurodeles waltl) pair; one of several salamandrids that can protrude its rib-tips through the skin on its flanks. Photo by Peter Halasz, licensed under Creative Commons Attribution-Share Alike 2.5 Generic, 2.0 Generic and 1.0 Generic license.

Another remarkable thing about salamandrids is that some species – and I’m thinking here of the Pleurodeles species (variously called sharp-ribbed newts or ribbed salamanders [adjacent photo by Peter Halasz]) – can (slightly) project the tips of their ribs out through their skin as a defensive tactic. Think about that for a minute. It’s badass. Neoteny occurs in some populations of some species, and viviparity has been evolved within two lineages.

Needless to say, there is tons more that could be said about the various salamander groups – there are hundreds of fascinating species that could all warrant detailed coverage on their own. But this very lengthy article is just meant to be an introduction to the group as a whole, not a comprehensive look at everything salamandry. I hope you enjoyed it, and there will be more amphibian-based goodness here at Tet Zoo in due time.

For previous Tet Zoo articles on salamanders, see…

Refs – -

Brazil, M. 1997. Mission massive. BBC Wildlife 15 (4), 62-67.

Carroll, R. & Zheng, A. 2012. A neotenic salamander, Jeholotriton paradoxus, from the Daohugou Beds in Inner Mongolia. Zoological Journal of the Linnean Society 164, 659-668.

Estes, R. 1969. The Batrachosauroididae and Scapherpetontidae, Late Cretaceous and Early Cenozoic salamanders. Copeia 1969, 225-234.

- . 1981. Handbuch der Paläoherpetologie. Teil 2. Gymnophiona, Caudata. Gustav Fischer Verlag, Stuttgart.

Evans, S. E., Lally, C., Chure, D. C., Elder, A. & Maisano, J. A. 2005. A Late Jurassic salamander (Amphibia: Caudata) from the Morrison Formation of North America. Zoological Journal of the Linnean Society 143, 599-616.

- . & Milner, A. R. 1996. A metamorphosed salamander from the early Cretaceous of Las Hoyas, Spain. Philosophical Transactions of the Royal Society of London B 351, 627-646.

Frost, D. R., Grant, T., Faivovich, J., Bain, R. H., Haas, A., Haddad, C. F. B., De Sá, R. O., Channing, A., Wilkinson, M., Donnellan, S. C., Raxworthy, C. J., Campbell, J. A., Blotto, B. L., Moler, P., Drewes, R. C., Nussbaum, R. A., Lynch, J. D., Green, D. M. & Wheeler, W. C. 2006. The amphibian tree of life. Bulletin of the American Museum of Natural History 297, 1-370.

Gao, K. & Shubin, N. H. 2001. Late Jurassic salamanders from northern China. Nature 410, 574-577.

- . & Shubin, N. H. 2003. Earliest known crown-group salamanders. Nature 422, 424-428.

- . & Shubin, N. H. 2012. Late Jurassic salamandroid from western Liaoning, China. Proceedings of the National Academy of Sciences, USA 109, 5767-5772.

Gardner, J. D. 2003. Revision of Habrosaurus Gilmore (Caudata; Sirenidae) and relationships among sirenid salamanders. Palaeontology 46, 1089-1122.

Gardner, J. D. 2003. The fossil salamander Proamphiuma cretacea Estes (Caudata; Amphiumidae) and relationships within the Amphiumidae. Journal of Vertebrate Paleontology 23, 769-782.

Gayet, M., Marshall, L. G., Sempere, T., Meunier, F. J., Capetta, H. & Rage, J.-C. 2001. Middle Maastrichtian vertebrates (fishes, amphibians, dinosaurs and other reptiles, mammals) from Pajcha Pata (Bolivia). Biostratigraphic, palaeoecologic and palaeobiogeographic implications. Palaeogeography, Palaeoclimatology, Palaeoecology 169, 39-68.

Halliday, T. R. & Verrell, P. 1986. Salamanders and newts. In Halliday, T. & Adler, A. (eds) Animals of the World: Reptiles and Amphibians. The Leisure Circle (Wembley, UK), pp. 18-29.

Larson, A. & Dimmick, W. W. 1993. Phylogenetic relationships of the salamander families: an analysis of congruence among morphological and molecular characters. Herpetological Monographs 7, 77-93.

Marjanović, D. & Laurin, M. 2007. Fossils, molecules, divergence times, and the origin of lissamphibians. Systematic Biology 56, 369-388.

Miller, L. 1944. Notes on the eggs and larvae of Aneides lugubris. Copeia 1944, 224-230.

Pryor, G. S., German, D. P. & Bjorndal, K. A. 2006. Gastrointestinal fermentation in greater sirens (Siren lacertina). Journal of Herpetology 40, 112-117.

Pyron, R. A. & Wiens, J. J. 2011. A large-scale phylogeny of Amphibia including over 2,800 species, and a revised classification of extant frogs, salamanders, and caecilians. Molecular Phylogenetics and Evolution 61, 543-583.

Rocek, Z. 1994. A review of the fossil Caudata of Europe. Abhandlungen und Berichte für Naturkunde 17, 51-56.

Sever, D. M., Sparreboom, M. & Schultschik, G. 1997. The dorsal tail tubercle of Mertensiella caucasica and M. luschani (Amphibia: Salamandridae). Journal of Morphology 232, 93-105.

Stebbins, R. C. 1966. A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin Company, Boston.

Trontelj, P. & Goricki, S. 2003. Monophyly of the family Proteidae (Amphibia: Caudata) tested by phylogenetic analysis of mitochondrial 12S rDNA sequences. Natura Croatica 12, 113-120.

Venczel, M. 1999. Land salamanders of the family Hynobiidae from the Neogene and Quaternary of Europe. Amphibia-Reptilia 20, 401-412.

Veith, M. & Steinfartz, S. 2004. When non-monophyly results in taxonomic consequences – the case of Mertensiella within the Salamandridae (Amphibia: Urodela). Salamandra 40, 67-80.

Wang, U. & Evans, S. E. 2006. A new short-bodied salamander from the Upper Jurassic/Lower Cretaceous of China. Acta Palaeontologica Polonica 51, 127-130.

Weisrock, D. W., Harmon, L. J. & Larson, A. 2005. Resolving deep phylogenetic relationships in salamanders: analyses of mitochondrial and nuclear genomic data. Systematic Biology 54, 758-777.

Wiens, J. J., Bonett, R. M. & Chippindale, P. T. 2005. Ontogeny discombobulates phylogeny: paedomorphosis and higher-level salamander relationships. Systematic Biology 54, 91-110.

Zhang, P., Chen, Y.-Q., Zhou, H., Liu, Y.-F., Wang, X.-L., Papenfuss, T. J., Wake, D. B. & Qu, L.-H. 2006. Phylogeny, evolution, and biogeography of Asiatic salamanders (Hynobiidae). Proceedings of the National Academy of Sciences 103, 7360-7365.

- ., Papenfuss, T. J., Wake, M. H., Qu, L. & Wake, D. B. 2008. Phylogeny and biogeography of the family Salamandridae (Amphibia: Caudata) inferred from complete mitochondrial genomes. Molecular Phylogenetics and Evolution 49, 586-597.

Darren Naish About the Author: Darren Naish is a science writer, technical editor and palaeozoologist (affiliated with the University of Southampton, UK). He mostly works on Cretaceous dinosaurs and pterosaurs but has an avid interest in all things tetrapod. His publications can be downloaded at darrennaish.wordpress.com. He has been blogging at Tetrapod Zoology since 2006. Check out the Tet Zoo podcast at tetzoo.com!

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The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. llewelly 6:15 am 10/1/2013

    ” Bizarrely, salamanders have disproportionately large amounts of DNA.”

    Bizarrely?

    Is there actually any evidence for a substantial relationship between skeletal complexity and amount of DNA?

    Link to this
  2. 2. Dartian 7:10 am 10/1/2013

    Mostly, this is because I somewhat dislike the use of the term ‘amphibian’ – mostly

    There, fixed it for you. ;) (Sorry for the obscure in-joke.)

    Link to this
  3. 3. David Marjanović 7:27 am 10/1/2013

    two species of Marmorerpeton

    Plus “Salamander A” and “Salamander B”, the latter possibly a urodele.

    Life reconstruction of a swimming Chunerpeton

    What, with no fin at all?

    One possibility is that noterpetontids are stem-sirens (Marjanović & Laurin 2007).

    Oh no, no, don’t cite us for that! We didn’t include the noterpetontids in any phylogenetic analysis (and neither has anyone else ever)! The tree we showed is just a hand-made supertree of trees and statements we found in the literature!

    Also, we updated it this year. I’ll send you the pdf in a few hours. :-)

    Fossil taxa extend the group’s history back to the Palaeocene (Estes 1981).

    David G. DeMar, Jr. (2013): A new fossil salamander (Caudata, Proteidae) from the Upper Cretaceous (Maastrichtian) Hell Creek Formation, Montana, U.S.A., JVP 33(3): 588–598.

    Abstract: “North American Late Cretaceous salamanders are principally known by isolated atlantes and trunk vertebrae. Here I describe a new genus and species of fossil salamander, Paranecturus garbanii, gen. et sp. nov., based on these elements from the lower portions of the Hell Creek Formation (Maastrichtian), Garfield Country, northeastern Montana, U.S.A. It is diagnosed by a unique combination of character states that include the presence of an alar-like process of the atlas and a groove on the posterior face of the neural arch and solid dorsal rib-bearers of the trunk vertebrae. My phylogenetic analysis of 13 caudate taxa and 23 atlantal and trunk vertebral characters [gah!] recovered P. garbanii as a member of the Proteidae. P. garbanii represents the oldest fossil record of the Proteidae and demonstrates that this lineage was present before the Cretaceous-Paleogene mass extinction event.”

    I didn’t know about the German sirenids, though. Or is that one of the misidentified… Anyway, I have to run, more later. :-(

    All Dicamptodon species have particularly solid-boned skulls

    …which are never illustrated in dorsal view. Not a single time in the literature I’ve seen.

    Link to this
  4. 4. naishd 7:41 am 10/1/2013

    Dammit, David: always complaining every single time I cite his papers!!

    Darren

    Link to this
  5. 5. naishd 7:44 am 10/1/2013

    … within that context, I should add that – when doing popular or semi-popular writing, as here – my philosophy on citing an article is that said citation functions to give the reader a source to refer to, should they want to chase it up; it is not necessarily shorthand for “here are the people who are responsible for demonstrating said fact”.

    Darren

    Link to this
  6. 6. Tomozaurus 7:53 am 10/1/2013

    “Habrosaurus, in fact, is so spectacular that I was half-expecting there to be some life restorations of it online… Alas, that doesn’t seem to be the case”

    Actually, I did reconstruct it here: http://tomozaurus.deviantart.com/art/Hell-Creek-Amphibian-sketch-dump-302266190 in sketch form with a selection of other Hell Creek lissamphibians, and I’ll be doing another, proper version in not too long.

    Link to this
  7. 7. naishd 8:55 am 10/1/2013

    Tomozaurus: thanks, I hadn’t seen this before, well done.

    Dartian (comment # 2): why don’t you put her in charge? Game over man, game over.

    Darren

    Link to this
  8. 8. Yodelling Cyclist 8:57 am 10/1/2013

    Awesome post. Is it just my misunderstanding, or was there really a salamander diversity explosion in the Upper Cretaceous? (Based on a quick reading of the above article alone).

    Link to this
  9. 9. keesey@gmail.com 9:27 am 10/1/2013

    “Evans & Milner (1996) argued that it makes better sense to use Caudata for the total-group … So Marmorerpeton and the karaurids Kokartus and Karaurus are stem-caudates but not urodeles.”

    The convention is usually (and most logically) to add “stem-” to the name of the crown group (e.g., stem-mammals, stem-avians, etc.), so it would be better to say they are caudates (=pan-urodeles), and more specifically stem-urodeles.

    Link to this
  10. 10. naishd 9:30 am 10/1/2013

    Mike (comment # 9): yeah, good call. That’s a part of the article I evidently didn’t update from 2008 (since, back then I was routinely not following what we now regard as convention).

    Darren

    Link to this
  11. 11. David Marjanović 11:07 am 10/1/2013

    Scapherpetontidae

    Scapherpetidae. Both by priority and by Greek grammar.
    Martín, C., Alonso-Zarazaga, M. A. & Sanchiz, B. 2012. Nomenclatural notes on living and fossil amphibians. Graellsia 68, 159–180.

    Red salamander (Pseudotriton rubber)

    The Spellchecker Strikes Back!!!

    Four-toed salamander (Hemidactylium scutatum), the only extant member of its lineage (and hence sometimes given its own ‘subfamily’, Hemidactylinae);

    Hemidactylium naturally gives Hemidactyliinae.

    Numerous other fossil taxa are known from between the Middle Oligocene and Pleistocene (including Archaeotriton, Brachycormus, Chelotriton, Megalotriton, Oligosemia, Palaeopleurodeles and Carpathotriton).

    Oligosemia is probably a synonym of Chelotriton. Megalotriton… I’m not sure why I ignored it so completely in my papers; perhaps because Estes (1981) had doubts about the validity of this taxon that’s founded on a few vertebrae. (He wondered about perhaps lumping it with Salamandra sansaniensis.)

    The very distinctive Spectacled salamander Salamandrina terdigitata of western Italy is generally recovered as the sister-taxon to the salamandrine + pleurodeline clade

    …No, that’s S. as a whole, also containing S. perspicillata!

    Also, while molecular studies always find S. in that position, morphological ones never do. But then, morphological phylogenetics of Salamandridae is really hard, due to neontological neglect of anatomy in general and skeletons in particular; also, Koaliella (three l, not 4) is only known from isolated vertebrae.

    The massive size of the Great crested newt (Triturus cristatus) alongside L. vulgaris (spotted throat) and L. helvetica (white throat, paler, less spotted underside) is notable.

    L[issotriton] helveticus of course.

    Is there actually any evidence for a substantial relationship between skeletal complexity and amount of DNA?

    No; the point here is that salamanders have much more junk DNA than all other vertebrates except lungfish. Correspondingly, they have unusually large cells.

    my philosophy on citing an article is that said citation functions to give the reader a source to refer to, should they want to chase it up; it is not necessarily shorthand for “here are the people who are responsible for demonstrating said fact”.

    Oh, I see.

    Anyway, the update is:
    Marjanović, D. & Laurin, M. 2013. An updated paleontological timetree of lissamphibians, with comments on the anatomy of Jurassic crown-group salamanders (Urodela). Historical Biology online-early, 16 pp.

    was there really a salamander diversity explosion in the Upper Cretaceous?

    Maybe, but what we can tell for sure is that the fossil record got a lot better then…

    The convention is usually (and most logically) to add “stem-” to the name of the crown group (e.g., stem-mammals, stem-avians, etc.)

    I don’t see what’s logical about that. Caudata consists of stem-caudates and crown-caudates. That’s how it’s been ever since Hennig, who only named total groups: every group consisted of its stem-group and its crown-group (“*-group” for Hennig).

    Link to this
  12. 12. naishd 11:11 am 10/1/2013

    Thanks, David.. I’ll make some appropriate corrections. Pseudotriton rubber, sigh… And I’d forgotten that there are two Salamandrina species. How embarrassing.

    Darren

    Link to this
  13. 13. ekocak 11:24 am 10/1/2013

    Really, really cool article. This is what I love about Tet. Zoo: Super geeky technical info written in a highly entertaining and accessible way. I’m honored to have been involved! Also, Darren, your artwork is excellent.

    Link to this
  14. 14. darkgabi 11:36 am 10/1/2013

    salamander, salamander, salamander la la la la!
    ^^

    ok, sorry.

    Link to this
  15. 15. ectodysplasin 12:09 pm 10/1/2013

    @David;

    >>All Dicamptodon species have particularly solid-boned skulls

    …which are never illustrated in dorsal view. Not a single time in the literature I’ve seen.

    Patience, patience.

    Link to this
  16. 16. ectodysplasin 12:18 pm 10/1/2013

    On the subject of fossil caudate diversity, there are a few problems.

    1. Most fossil salamanders are extremely small, so you’re only going to find them in microvertebrate assemblages, and Mesozoic microvertebrates are undersampled.

    2. Fossil salamanders do turn up in lacustrine deposits relatively regularly, but in these cases you really only get a few species of salamander per lake system, much like modern ecosystems. Modern salamanders are simply not diverse, and it appears that fossil salamanders weren’t either.

    3. There does seem to be a real diversification in the Cretaceous. This may be part of the “Cretaceous Terrestrial Revolution.”

    Link to this
  17. 17. ectodysplasin 12:26 pm 10/1/2013

    By the way, the modern biodiversity hotspot for salamanders is the Great Smokey Mountain National Park in the southern Appalachians. The vast majority of this diversity is plethodontid, but there are also proteids, salamandrids, ambystomatids, and the cryptobranchid Cryptobranchus. A small group of us actually went out there last year before SVP and saw ~6-7 species of plethodontid, mostly Plethodon and Desmognathus. This year will have no such luck…not many salamanders in the Los Angeles area.

    Link to this
  18. 18. keesey@gmail.com 12:39 pm 10/1/2013

    In response to David Marjanović (#11):

    It makes more sense because crown groups are more likely to be named, because they’re more likely to have good specimens. Huge swathes of biology have little or nothing but extant specimens. So it makes sense to have the main name refer to the crown, with prefixes (“pan-”, “stem-”) for the total and stem groups. (And “apo-” for the apomorphy-based clade, when the name refers to an apomorphy.)

    (To really avoid ambiguity you could require a prefix for crown groups, too, but who wants to do that?)

    Link to this
  19. 19. ekocak 12:42 pm 10/1/2013

    I live north of there, but still routinely find Ambystoma maculatum and jeffersoni (and what i think are intergrades of the 2), Plethodon cinereus EVERYWHERE, and occasional Necturus. Never seen a hellbender outside of a zoo, but they’re only at the southern tip of NY and I live in the central region. Still, that’s pretty amazing diversity. Hadn’t thought about that until you pointed it out, ectodysplasin.

    Link to this
  20. 20. ectodysplasin 1:33 pm 10/1/2013

    There’s apparently a healthy population of hellbenders in north-central Pennsylvania, according to a friend of mine who does wetlands monitoring up in that region. I used to see them occasionally in southwest PA down into the Laurel Highlands, but yes, there’s a ton of diversity right up and down the Appalachians.

    Salamanders are essentially unique among tetrapods in that they have a MUCH higher diversity at higher latitudes and a relatively lower diversity at lower latitudes. In fact, the vast majority of family-level diversity is limited to the continental US and tiny bits of southern British Columbia. The vast majority of proteid diversity is North American. All dicamptodontids are. All sirenids are. All amphiumids are. All rhyacotritonids are. And one of the two genera of cryptobranchid is. Most ambystomatid diversity is. And so on.

    This raises some interesting questions about caudate origins and biogeography, as well. Caudates are almost entirely laurasian; a few species have made their way into South America and North Africa very recently, but the group is almost exclusively boreal. This is not the case for essentially any other group. Frogs, for instance, had no problem colonizing Africa, South America, Australia, and Madagascar. Is caudate diversity uniquely restricted to cooler more temperate climates for physiological reasons? If so, how long have caudates been restricted to the north? Could this biogeographic restriction pre-date the breakup of Pangaea?

    Lots to chew on there.

    Link to this
  21. 21. Andreas Johansson 1:43 pm 10/1/2013

    So what do giant salamander lungs function in? Bouyancy control?

    Link to this
  22. 22. Halbred 4:25 pm 10/1/2013

    If anybody does the TMNT as caudates, Michelangelo would be an axlotl.

    Link to this
  23. 23. Chelydra 12:33 am 10/2/2013

    Jefferson salamander, not Jefferson’s – named for Jefferson College, Pennsylvania, hence the neuter, place-of-origin suffix.

    Ambystoma are really turning out truly bizarre. The normal diploid species apparently never hybridize. The all-female species (“unisexual salamander” seems to be a commonly used name) is triploid (or higher), consisting of what usually look like F1 hybrids involving barbouri, jeffersonianum, texanum, tigrinum, and always laterale. Despite this, they are apparently a single lineage with mitochondrial DNA closest to barbouri. Although the unisexuals normally produce female offspring identical to themselves, they apparently have the ability to mate with males of these five species and swap out an entire set of chromosomes for a new set, with little or no crossing over. Unisexuals are really common, often the dominant species in a pond. One theory is that when an individual disperses to a new habitat, she mates with males of the most common species there, which is presumably best adapted for that location. Then, within just a generation or two, her offspring essentially become that species as well!

    Link to this
  24. 24. naishd 4:04 am 10/2/2013

    Many thanks to all for great comments.

    “Jefferson salamander, not Jefferson’s” (comment # 23). Of course, d’oh!

    Ambystoma as gene-stealer… bizarre sci-fi stuff…

    Darren

    Link to this
  25. 25. darkgabi 5:56 am 10/2/2013

    doesn’t a bizarre gene thing also happen in some hybridizing frog somewhere here in europe? but i have the feeling it was a kick-out instead of gene-stealing – so the invading frog actually dominates and transforms the local population in its own species.

    lissamphibians are as weird as plants.
    never trust an organism that can be XN where x > 2

    Link to this
  26. 26. naishd 6:44 am 10/2/2013

    darkgabi: pretty sure you’re thinking of the hybridogenetic Pelophylax water frogs. I’d try and explain it, but I don’t have a spare hour today… Some discussion in this Tet Zoo article from 2011.

    Darren

    Link to this
  27. 27. darkgabi 7:05 am 10/2/2013

    yes! thanx ^^
    hemiclonal species that is. weeeeeeird.

    Link to this
  28. 28. josimo70 8:08 am 10/2/2013

    herpeton is Greek neuter, so its root is herpeto-, and not herpeton- or herpetont-. The same is valid for Hipparion. If herpeton is Latinized, it must turn into herpetum. No n-suffix (as in Iason) or nt-suffix (as in phaethon, medon, leon).

    Link to this
  29. 29. Chabier G. 8:49 am 10/2/2013

    About hearing in newts, I found very surprising this paper, as I thought newts were almost deaf for high pitched sounds, and not able to show such a complex behaviour:

    http://link.springer.com/article/10.1007%2Fs00265-003-0740-y#

    Link to this
  30. 30. David Marjanović 9:56 am 10/2/2013

    Patience, patience.

    Butbutbut I should have finished the salamandrid phylogeny manuscript long ago, and I need Dicamptodon as an ouuuuuutgrouuuuup… *sniff*

    It makes more sense because crown groups are more likely to be named, because they’re more likely to have good specimens. Huge swathes of biology have little or nothing but extant specimens.

    Point taken… I’m not sure about Hennig, who probably never thought about the question, but his successor Ax wants to name only total groups.

    Then, within just a generation or two, her offspring essentially become that species as well!

    O_o

    Link to this
  31. 31. David Marjanović 10:00 am 10/2/2013

    http://link.springer.com/article/10.1007%2Fs00265-003-0740-y#

    “Purchase on Springer.com
    $39.95 / €34.95 / £29.95 *
    * Final gross prices may vary according to local VAT.”

    How high is the lowest frequency of these toad calls? Salamanders (like frogs and possibly Eocaecilia) do have the opercular system that allows them to hear low frequencies.

    Link to this
  32. 32. vdinets 10:17 am 10/2/2013

    ectodysplasin: there are a few groups that show similar biodiversity patterns, crayfish, for example. But in a vast majority of groups that are most diverse in the so-called Tertiary refugia, the diversity is much higher in and around China than in eastern North America. So the question here is not why there are so many species in North America, it’s what happened to the ones in China.

    Link to this
  33. 33. vdinets 10:22 am 10/2/2013

    Also, note that there is plenty of salamander species described from southern Mexico (many of them probably extinct by now due to habitat loss), but for some reason they didn’t manage to diversify further south.

    Link to this
  34. 34. Heteromeles 10:56 am 10/2/2013

    Don’t forget that some Ambystoma (at least A. maculatum also appear to be photosynthetic, at least as embryos (go here). Science fictional indeed.

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  35. 35. Dartian 12:14 pm 10/2/2013

    Darren (OP):
    The identification of these fossils – some of which have often been united in a group termed Noterpetontidae – as sirenids has been challenged (Gardner 2003).

    Is there a source for the idea that these Gondwanan sirenids may actually be something else? I had a look at Gardner (2003) but unless I missed something, he doesn’t seem to actually discuss these purported Sudanese and Bolivian sirenids at all.

    ectodysplasin:
    Salamanders are essentially unique among tetrapods in that they have a MUCH higher diversity at higher latitudes and a relatively lower diversity at lower latitudes.

    They are not unique in this regard. ‘Family’-level and higher taxa that are more diverse/speciose at higher than at lower latitudes include (off the top of my head) at least lagomorphs, beaver-like rodents (i.e., castorimorphs), voles (regarded as a mere ‘subfamily’ by some workers, but that’s of course rather subjective), mustelids, pinnipeds, moles, waterfowl, penguins, charadriforms, cranes, and true finches (fringillids); and possibly sciurids, motacillids, and terrapins as well. And that’s ignoring small ‘families’ with less than ten species or so. If we go beyond tetrapods – but remain within Vertebrata – we’ll discover that an urodele-like distribution pattern isn’t all that uncommon among freshwater fish (even though many such fish ‘families’ and ‘orders’ are as old or older than salamanders).

    a few species have made their way into South America and North Africa very recently, but the group is almost exclusively boreal

    That last part is actually not quite true either. Only a few salamanders have penetrated the continent of South America, true, but there are lots and lots of plethodontid species in the Neotropical parts of Central America (admittedly some of these species live at high altitudes where conditions aren’t exactly tropical, but there are plenty of salamander species that do live in the lowland rainforests of Mesoamerica). In fact, at the level of species, salamanders reach their highest diversity in the Neotropical Region; there are more than 250 species there (Vences & Köhler, 2008). So considering that a highly significant proportion of the extant urodele species actually live in a tropical region, it’s a bit misleading to say that salamanders are “almost exclusively boreal”.

    Is caudate diversity uniquely restricted to cooler more temperate climates for physiological reasons?

    Seems a bit unlikely, considering the diversity of this particular clade (if the reasons are physiological, then what would they be?). Personally, I’d be more willing to bet that the reason is mainly ecological. I mentioned fish earlier; they might be key actors here.

    Most amphibians need water for reproduction, and if that water is infested with fish that’s bad news indeed for the amphibians. Fish are serious predators of tadpoles (and, to a lesser extent, amphibian eggs); fish are much more effective amphibian predators than, e.g., dragonfly nymphs and diving beetles; when present, fish may actually eliminate tadpole populations entirely (e.g., Heyer et al., 1975; cf. Hecnar & M’Closkey, 1997).

    In temperate regions, there are often relatively more fish-free water bodies available for amphibians than in the tropics. Few non-tropical fish are well adapted to small ephemeral water bodies, and fewer still to ponds and small water bodies that freeze entirely during winter (depriving fish of oxygen). In the tropics, by contrast, there are many fish species that are not only able to survive in such small and short-lived water bodies but are also pretty good at dispersing to them (Heyer et al., 1975).

    Anurans have responded to the problem of fish predation by evolving elaborate avoidance mechanisms such as laying their eggs high up in trees (Magnusson & Hero, 1991). Salamanders seem to have been less ‘innovative’ in this regard, and by being slower-moving than anurans they might be more vulnerable to fish predators even as adults. This, I suspect, is a more likely general reason for the absence of salamanders from most parts of the world’s tropics than any physiological one.

    (Come to think of it, by being slow-moving salamanders might be relatively more vulnerable in many tropical land environments too than many similar-sized tetrapods. Would even the strongest poison be enough to protect a salamander that was unlucky enough to happen to get in the way of a troop of army ants…?)

    how long have caudates been restricted to the north? Could this biogeographic restriction pre-date the breakup of Pangaea?

    To learn the answer to that question, look up San Mauro et al. (2005). There’s even a clue in the title… ;)

    References:

    Hecnar, S.J. & M’Closkey, R.T. 1997. The effects of predatory fish on amphibian species richness and distribution. Biological Conservation 79, 123-131.

    Heyer, W.R., McDiarmid, R.W. & Weigmann, D.L. 1975. Tadpoles, predation and pond habitats in the tropics. Biotropica 7, 100-111.

    Magnusson, W.E. & Hero, J.-M. 1991. Predation and the evolution of complex oviposition behaviour in Amazon rainforest frogs. Oecologia 86, 310-318.

    San Mauro, D., Vences, M., Alcobendas, M., Zardoya, R. & Meyer, A. 2005. Initial diversification of living amphibians predated the breakup of Pangaea. The American Naturalist 165, 590-599.

    Vences, M. & Köhler, J. 2008. Global diversity of amphibians (Amphibia) in freshwater. Hydrobiologia 595, 569-580.

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  36. 36. Heteromeles 1:45 pm 10/2/2013

    In temperate regions, there are often relatively more fish-free water bodies available for amphibians than in the tropics. Few non-tropical fish are well adapted to small ephemeral water bodies, and fewer still to ponds and small water bodies that freeze entirely during winter (depriving fish of oxygen). In the tropics, by contrast, there are many fish species that are not only able to survive in such small and short-lived water bodies but are also pretty good at dispersing to them (Heyer et al., 1975).

    Ummm. There are plenty of frogs in the tropics, so I don’t think that’s it.

    My impression is that the tropics are home to a large number of salamander-sized lizards. One key advantage the amphibians have is that they’re relatively more cold-tolerant than are lizards. A number of amphibians can freeze solid, but very few (if any) lizards have managed that trick. As one goes north (or uphill) in North America, the number of reptiles drops off dramatically, but not the number of salamanders and frogs.

    I’d therefore suggest that the critical filter is cold temperatures. Under year-round warmth, lizards may be able to exclude salamanders, or exile them to marginal and exotic niches (as with Batrachoseps). In areas with a pronounced cool season, the advantage starts shifting to the more cold-tolerant amphibians. I’m not sure where the dividing line is, but it’s probably near where I live in southern California. We get frogs, toads, and the occasional Batrachoseps on wet winter nights, alligator lizards in the spring, and fence lizards and skinks in the summer and fall.

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  37. 37. Yodelling Cyclist 2:48 pm 10/2/2013

    Might this not be a dissolved oxygen question? It seems – again, from limited knowledge, that we could look at this problem as there being more salamander species in the north than the tropics, not because the tropics are species defficient, but because the northern lattitudes permit greater diversity. I raise this because several of the northern/cold temperature adapted groups discussed above seem to be either semi or wholly aquatic, whilst the tropical species seem to be more likely to be the more terrestrial species. Could it simply be that, where there is more dissolved oxygen, salamanders cheerfully evolve into aquatic niches which are otherwise denied them in warmer conditions? This is a bit counter intuitive (given the number of tropical fish that breathe air), but it seems to fit a pattern. Or is it that we should be looking at why fish are less diverse in boreal environments?

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  38. 38. Heteromeles 2:51 pm 10/2/2013

    Well, I’ve seen tadpoles gulping air in vernal pools. I’m not sure how many of them (including tropical fish) are strictly dependent on skin/gill breathing.

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  39. 39. Chelydra 3:36 pm 10/2/2013

    Cool – I was unaware of Pelophylax hybridogenesis.

    Curiously, although all the unisexual Ambystoma variants have at least one laterale genome, they never have *only* laterale. Unisexuals overlap entirely in range, habitat and breeding time with A. maculatum, but never hybridize with them.

    Some ridiculous tetraploid individuals have one genome from each of four species!

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  40. 40. vdinets 4:37 pm 10/2/2013

    Note that on family level, about a half of North American salamander diversity (amphiumas, sirens, mudpuppies, newts, and mole salamander larvae) routinely live in bodies of water with very high summer temperature, plenty of fish, and low oxygen content. The only ones that are clearly limited to cold, clear streams are hellbenders, torrent salamanders and aquatic lungless salamanders. Mole salamanders do breed in vernal pools, but they can also breed in permanent ponds that have fish.

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  41. 41. keesey@gmail.com 5:09 pm 10/2/2013

    “there are a few groups that show similar biodiversity patterns, crayfish, for example” -vdinets

    Come to think of it, salamanders and crayfish have always seemed to me to be found in the exact same spots. Could their biogeography be explained by something they have in common?

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  42. 42. Yodelling Cyclist 5:32 pm 10/2/2013

    @vdinets: Sure, half the North American diversity handles warm low oxygen environments. If my suggestion holds water, the other half, the “extra” half if compared with tropical habitats, does cold, high oxygen environment streams.

    @keesey: what are the general requirements for a crayfish?

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  43. 43. ectodysplasin 7:27 pm 10/2/2013

    @David,

    Butbutbut I should have finished the salamandrid phylogeny manuscript long ago, and I need Dicamptodon as an ouuuuuutgrouuuuup… *sniff*

    Can’t you just cite the digimorph data?

    http://digimorph.org/specimens/Dicamptodon_ensatus/

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  44. 44. ectodysplasin 7:32 pm 10/2/2013

    @vdinets:

    Also, note that there is plenty of salamander species described from southern Mexico (many of them probably extinct by now due to habitat loss), but for some reason they didn’t manage to diversify further south.

    Yes, but with important caveats. Mexican ambystomatids are all from areas of high altitude (~2200 m) as are most Central American plethodontids. Aaaand, that’s it for southern diversity. So yes, there’s some diversity at lower latitudes, but it mostly sticks to areas of high altitude.

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  45. 45. ectodysplasin 8:03 pm 10/2/2013

    @Dartian;

    They are not unique in this regard. ‘Family’-level and higher taxa that are more diverse/speciose at higher than at lower latitudes include (off the top of my head) at least lagomorphs, beaver-like rodents (i.e., castorimorphs), voles (regarded as a mere ‘subfamily’ by some workers, but that’s of course rather subjective), mustelids, pinnipeds, moles, waterfowl, penguins, charadriforms, cranes, and true finches (fringillids); and possibly sciurids, motacillids, and terrapins as well. And that’s ignoring small ‘families’ with less than ten species or so.

    Except we’re not talking about family-level diversity, which can be more or less endemic. We’re talking about a lineage that dates back at least as far as the early Triassic that has remained almost completely out of the tropics and has never crossed into Gondwana, despite having existed for the entirety of the Mesozoic.

    If we go beyond tetrapods – but remain within Vertebrata – we’ll discover that an urodele-like distribution pattern isn’t all that uncommon among freshwater fish (even though many such fish ‘families’ and ‘orders’ are as old or older than salamanders).

    Untrue. There are only a handful of “fish” stem-groups that are as old as the earliest Triassic; there’s the Elasmobranchi, there’s the Holocephali, there’s the Myxinoidea, there’s the Petromyzontiformes, there’s the Chondrostei, there’s the Cladistia, there’s the Actinistia, there’s the Lepidosireniformes, there’s the Ceratodontiformes, there’s the Holostei, and there’s the Teleostei. That’s it.

    As far as fish with boreal distributions, that applies to Chondrostei (although chondrosteans have had a cosmopolitan distribution in the past), Holostei (once again, cosmopolitan in the past) and a few salmoniform clades such as salmonids (which are specifically recent colonizers of waterways that were completely frozen over during the Pleistocene glaciation). Not much else.

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  46. 46. ectodysplasin 8:24 pm 10/2/2013

    Continued…

    That last part is actually not quite true either. Only a few salamanders have penetrated the continent of South America, true, but there are lots and lots of plethodontid species in the Neotropical parts of Central America (admittedly some of these species live at high altitudes where conditions aren’t exactly tropical, but there are plenty of salamander species that do live in the lowland rainforests of Mesoamerica). In fact, at the level of species, salamanders reach their highest diversity in the Neotropical Region; there are more than 250 species there (Vences & Köhler, 2008). So considering that a highly significant proportion of the extant urodele species actually live in a tropical region, it’s a bit misleading to say that salamanders are “almost exclusively boreal”.

    Neotropical plethodontids are mostly high altitude, which doesn’t really make your case very well for you, and the majority of plethodontid diversity is still temperate in distribution, in areas like the Cascades and the Appalachians. Within the plethodontids, only a single clade has really adapted for tropical environments, and that’s the bolitoglossinae. Furthermore, whereas diversity of bolitoglossines along tropical portions of the American cordillera is highly endemic (i.e. the species on one mountain is different from the species on the next) the diversity in the southern Appalachians all lives basically right on top of each other. You can flip a log and see 3-4 genera of salamander living right next to each other, easily. You see a similar level of diversity in the Cascades. You don’t see this sort of diversity in the Tropics.

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  47. 47. vdinets 8:25 pm 10/2/2013

    keesy (#41): Sure. Like what?

    Yodelling Cyclist (#42): although almost all Asian salamanders live in cold streams, not that many American ones do. Most lungless salamanders live on the forest floor, in seepages, rock crevasses, at cave entrances and in other moist terrestrial microhabitats. It is still possible that cold streams were their ancestral habitat (and the earliest split, the 4toed salamander, still lives there).

    ectodysplasin (#42): So it looks like their distribution in the tropics is limited by either temperature or some lowland factor like reptiles or ants? But they still managed to cross Panama…

    ectodysplasin (#43):It looks like gars and, to some extent, bowfins (with the sample size of one, but still…) have somewhat similar distribution. And sturgeons, although their diversity is much less North America-centered.

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  48. 48. Raskos 8:27 pm 10/2/2013

    Amphiumas are reportedly of unpleasant temperament and are said to bite savagely

    Oh, very true – I still have the scar over 30 years later. Although it was not due to an unpleasant temperament on the part of the amphiuma so much as it getting overly excited at the thought of being fed and me not realizing that it could strike above the water’s surface.

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  49. 49. ectodysplasin 8:29 pm 10/2/2013

    @vdinets:

    Note that on family level, about a half of North American salamander diversity (amphiumas, sirens, mudpuppies, newts, and mole salamander larvae) routinely live in bodies of water with very high summer temperature, plenty of fish, and low oxygen content. The only ones that are clearly limited to cold, clear streams are hellbenders, torrent salamanders and aquatic lungless salamanders. Mole salamanders do breed in vernal pools, but they can also breed in permanent ponds that have fish.

    Bingo. Fish are clearly not a limiting factor for amphiumids, sirenids, proteids, or cryptobranchids. They are a limiting factor for some ambystomatids and some salamandrids, but certainly not all. They are not a limiting factor for rhyacotritonids or metamorphosing plethodontids (which tend to inhabit small montane streams not hospitable for fish), and direct-developing plethodontids are completely free from the effects of fish more generally.

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  50. 50. ectodysplasin 8:38 pm 10/2/2013

    @vdinets:

    ectodysplasin (#42): So it looks like their distribution in the tropics is limited by either temperature or some lowland factor like reptiles or ants? But they still managed to cross Panama…

    My gut feeling is that it’s water availability that’s the issue. Montane environments make their own weather, which would explain why the American cordillera has been the primary route by which salamanders have finally colonized South America. Unlike frogs, only a few salamander groups have really managed to figure out how to handle vernal pools in otherwise arid to semiarid environments…basically A. tigrinum-complex Ambystoma and that’s essentially it. Frogs, on the other hand, are much, much better at this.

    Also worth pointing out is that these biogeographic barriers seem to date back to the Triassic or Jurassic, long before we see modern squamate diversity and long before the origin of ants. So, they\re probably not the limiting factor.

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  51. 51. ectodysplasin 8:51 pm 10/2/2013

    @vdinets:

    ectodysplasin (#43):It looks like gars and, to some extent, bowfins (with the sample size of one, but still…) have somewhat similar distribution. And sturgeons, although their diversity is much less North America-centered.

    Both bowfins and gars used to have cosmopolitan distributions (see Grande & Bemis 1998 for a review of amiiform diversity and distribution), but that’s been lost, probably due in no small part to competition from teleosts. Gars are, today, still rather tropical fishes; three of the seven species have tropical distributions.

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  52. 52. ectodysplasin 8:53 pm 10/2/2013

    As for sturgeon diversity, sturgeons are anadromous and seem to do more or less what salmonids do; they’re most successful in recent river systems that were previously emptied of diversity by the Pleistocene glaciation.

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  53. 53. vdinets 9:48 pm 10/2/2013

    ectodysplasin:
    (#50): But most, if not all, neotropic salamanders don’t have an aquatic stage. Could it be that their colonization of the neotropics has happened during some colder part of the Pleistocene, when all Central American lowlands were simply too dry for them, and their invasion of the lowlands is even more recent?

    (#51) Cuban gar is possibly a descendant of alligator gars that crossed the strait during one of the glaciations (alligator gar is frequently caught in the sea). Let’s ask the same question the other way: what was so special about eastern North America that allowed both gars and salamanders (and crayfish) to survive there better than anywhere else?

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  54. 54. Heteromeles 12:30 am 10/3/2013

    The explanation for the high diversity of plants in the southeast US is the Appalachians. Because they run NE/SW, rather than forming an E/W barrier wall like the Alps or the Himalayas. During glaciations, the Alps and the Himalayas prevented animals from migrating south to avoid the ice. In the Appalachians (and in California), the mounts ran more parallel to the ice advance, and so organisms could migrate and find refugia. Ditto for altithermal periods.

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  55. 55. Dartian 6:08 am 10/3/2013

    Heteromeles:
    There are plenty of frogs in the tropics, so I don’t think that’s it.

    In my comment, did you miss the paragraph following the one that you directed your remark at? I said there that many frogs have evolved successful strategies that allow them to escape fish predation – for example by laying their eggs up in trees. Hence their success in the tropics. Salamanders might be less adaptable in this regard – but it’s interesting to note that many Neotropical plethodontids are arboreal too (although they’re also live-bearing).

    As one goes north (or uphill) in North America, the number of reptiles drops off dramatically, but not the number of salamanders and frogs.

    That’s not universally the case. In Europe, for example, there is no such distribution pattern at least not latitude-wise. Both amphibians (Rana temporaria, Rana arvalis, Bufo bufo) and reptiles (Zootoca vivipara, Vipera berus) reach about equally far north (i.e., to the Arctic Circle and even slightly further north); the lizard Z. vivipara actually ranges the furthest north of them all, penetrating even the sub-arctic zone.

    Vlad:
    about a half of North American salamander diversity (amphiumas, sirens, mudpuppies, newts, and mole salamander larvae) routinely live in bodies of water with very high summer temperature, plenty of fish

    They may technically live in the ‘same’ body of water but they may still be utilising significantly different parts of it. The presence of fish is likely to have a very strong effect on microhabitat choice in salamanders (e.g., Petranka, 1983).

    ectodysplasin:
    Except we’re not talking about family-level diversity

    Whoa, hold your backtracking horses, Batman! You are trying to move the goalposts. This is what you wrote in comment #20 (emphasis mine):

    Salamanders are essentially unique among tetrapods in that they have a MUCH higher diversity at higher latitudes and a relatively lower diversity at lower latitudes. In fact, the vast majority of family-level diversity is limited to the continental US and tiny bits of southern British Columbia. The vast majority of proteid diversity is North American. All dicamptodontids are. All sirenids are. All amphiumids are. All rhyacotritonids are. And one of the two genera of cryptobranchid is. Most ambystomatid diversity is. [...] Caudates are almost entirely laurasian; a few species have made their way into South America and North Africa very recently, but the group is almost exclusively boreal. This is not the case for essentially any other group.

    You were not specifying what (Linnaean) taxonomic level you were operating with; to the contrary, you even specifically listed a bunch of ‘families’ to make your point. Thus your statement, as you yourself worded it, was just factually incorrect, plain and simple (as there are other tetrapod families and orders with predominantly high-latitude distributions). If you don’t express yourself clearly, others will misunderstand you – and it is then your fault, not theirs.

    We’re talking about a lineage that dates back at least as far as the early Triassic that has remained almost completely out of the tropics and has never crossed into Gondwana, despite having existed for the entirety of the Mesozoic.

    So what about those Mesozoic South American and African sirenid fossils that Darren mentioned? Are you suggesting that they’ve been misidentified?

    fish with boreal distributions

    Side note: In biogeography and ecology, the term ‘boreal’ has a very specific meaning. In this thread, you are misusing it.

    As for ‘fish’ clades that are more diverse at higher than at lower latitudes, apart from the already mentioned there are also at least esociforms, osmeriforms, and gasterosteiforms, and the lampreys (although they of course aren’t fish).

    which doesn’t really make your case very well for you

    Pfft. It wasn’t my case. I was pointing out flaws in your case. In this particular instance, you claimed that (to use your exact words) caudates are “almost exclusively boreal”. Which is factually incorrect, considering that about 45% of the extant salamander species live south of the Tropic of Cancer.

    the majority of plethodontid diversity is still temperate in distribution

    I’ll give credit where it’s due: good on you for using here the term ‘temperate’ instead.

    You don’t see this sort of diversity in the Tropics.

    Do you mean diversity in terms of genera? If so, first define what a ‘genus’ is among salamanders. (And good luck with advocating the Linnaean ranks on this blog!)

    Fish are clearly not a limiting factor for amphiumids, sirenids, proteids, or cryptobranchids.

    How do you know that? Has this actually been studied, and if so, by whom?

    rhyacotritonids or metamorphosing plethodontids (which tend to inhabit small montane streams not hospitable for fish), and direct-developing plethodontids are completely free from the effects of fish more generally

    I don’t follow your logic. Why do you think that kind of reproductive strategies evolved in the first place? How do you know that they didn’t evolve because fish (or possibly some other aquatic predators) were/are such a big problem for salamanders? That, by the way, is not merely my opinion; David B. Wake, who knows a thing or two about salamanders (especially Neotropical plethodontids), has suggested that too (e.g., Wake, 1987).

    Both bowfins and gars used to have cosmopolitan distributions (see Grande & Bemis 1998 for a review of amiiform diversity and distribution), but that’s been lost, probably due in no small part to competition from teleosts.

    First you suggested that salamanders are unable to penetrate the tropics because of physiological reasons (ignoring the fact that dozens of salamander species have actually spread to tropical rainforest habitats in Central and South America), and dismissed ecological explanations (specifically, interactions with fish). Now you’re saying that bowfins and gars were eliminated from the tropics because of ecological reasons (specifically, competition with teleosts). Why do you casually propose ecological reasons in some cases and then equally casually dismiss them in other cases?

    Vlad:
    Could it be that their colonization of the neotropics has happened during some colder part of the Pleistocene

    No, the Neotropical plethodontid clades originated long before the Pleistocene, suggesting a very long history in this region (Parra-Olea et al., 2004).

    References:

    Parra-Olea, G., García-París, M. & Wake, D.B. 2004. Molecular diversification of salamanders of the tropical American genus Bolitoglossa (Caudata: Plethodontidae) and its evolutionary and biogeographical implications. Journal of Biogeography 81, 325-346.

    Petranka, J.W. 1983. Fish predation: a factor affecting the spatial distribution of a stream-breeding salamander. Copeia 1983, 624-628.

    Wake, D.B. 1987. Adaptive radiation of salamanders in Middle American cloud forests. Annals of the Missouri Botanical Garden 74, 242-264.

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  56. 56. vdinets 9:16 am 10/3/2013

    OK, let’s summarize the questions. I’ll ignore isolated cases like olms and Korean lungless salamander for now.

    1. Why large, fully aquatic salamanders inhabiting stagnant or slow-moving bodies of water with plenty of fish (sirens, amphiumas, mudpuppies) have survived only in Eastern North America?

    2. Why did different families survive on different continents and in different ways? Hynobiids survived only in Asia, and, as far as I remember, all but one inhabit fast, cold streams (with plenty of predatory Salmonids in some cases). Plethodontids survived in North America and diversified by successfully colonizing terrestrial habitats.

    3. Why didn’t Plethodontids diversify in tropical lowlands?

    I don’t know the answers, but I suspect that very cold and dry Chinese winters (probably even worse in Pleistocene) might have killed all terrestrial species, or any attempt to evolve such. There are, of course, newts in china, but they are not skin-breathers and have rough skin, so my guess would be they are more drought-resistant. Mountains don’t run east-west in China, but moving south probably wasn’t a good idea because Indochina has very pronounced dry season (unlike the Gulf of Mexico coast).

    Now, when the sea level dropped in Pleistocene, huge swampy estuaries probably became a rarity as the lower stretches of rivers became mid-stretches and the new lower stretches were quickly cutting into soft marine sediment. But the northern part of the Gulf of Mexico is so shallow for many miles offshore that the swamps persisted. That’s why this area still has uniquely diverse flora and fauna of swamps and slow rivers, with swamp-adapted trees (even pines and oaks), rabbits, and, of course, giant eel-like salamanders. In eastern China, similar areas occur only in the north, and were probably too cold for anything like it. Just a guess.

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  57. 57. Heteromeles 9:38 am 10/3/2013

    @56: and don’t forget that the Himalayas kept Chinese salamanders from migrating south into Vietnam or India when the climate got too cold in China.

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  58. 58. Gigantala 10:02 am 10/3/2013

    I’m just going to throw in my two cents and state that competition/predation from bony fish probably isn’t the reason because A) salamanders didn’t seem to have suffered a drop in diversity during the Palaeogene, when the range of fish adapted to temporary water resources had expanded, and B) because salamanders didn’t kick the bucket when teletosts diversified and killed off earlier bony fishes.

    I don’t think we know nearly enough about the Jurassic of Gondwanna fossil reccord to assess whereas salamanders were there or not. It’s entirely possible that they were but somehow disappeared from the southern continents in the Cretaceous.

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  59. 59. vdinets 11:05 am 10/3/2013

    Heteromeles (#57) there are no sufficiently high mountains between China and Vietnam. Also, note that (a) Hynobiids did make it to the southern side of Himalaya-Hundukush mountains, and occur in Kabul Valley; (2) newts did make it into Vietnam and also to the southern slope of the Himalaya, all the way to Nepal.

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  60. 60. ectodysplasin 1:32 pm 10/3/2013

    @vdinets:

    ectodysplasin:
    (#50): But most, if not all, neotropic salamanders don’t have an aquatic stage. Could it be that their colonization of the neotropics has happened during some colder part of the Pleistocene, when all Central American lowlands were simply too dry for them, and their invasion of the lowlands is even more recent?

    That doesn’t seem to hold up as far as phylogenetic treatments of the question go.

    (#51) Cuban gar is possibly a descendant of alligator gars that crossed the strait during one of the glaciations (alligator gar is frequently caught in the sea). Let’s ask the same question the other way: what was so special about eastern North America that allowed both gars and salamanders (and crayfish) to survive there better than anywhere else?

    That doesn’t explain the presence of A. tropicus along the Caribbean coast of Central America. Atrachosteus is a tropical genus that has migrated in and out of the continental US as the temperature has gone up and down throughout the Cenozoic. This also goes for various other neotropical taxa that show up in Florida and South Texas, such as Drymarchon, and so on, as well as fossil members of the Corytophanidae, Boidae, and various other neotropical taxa that show up in, say, Wyoming around the PETM.

    Remember, a lot of the reptiles we think of today as “South American” have North American roots. These are animals that generally evolved alongside North American caudates throughout the Cenozoic, but were extirpated from the US and Canada due to late Cenozoic glaciation.

    So more generally, the North American fauna and differences between the North American fauna and other faunas is due to a number of factors, including extirpations, migrations, and barriers to migration. With gars, modern distribution does not reflect fossil distribution and clearly indicates stepwise extirpation from various regions. Same with bowfins. While absence of some salamander taxa in Europe and Asia seems to be the result of extirpation, absence in South America, Africa, and Australia seems to be the result of dispersal barriers.

    Link to this
  61. 61. ectodysplasin 2:03 pm 10/3/2013

    @Dartian:

    So what about those Mesozoic South American and African sirenid fossils that Darren mentioned? Are you suggesting that they’ve been misidentified?

    No, although I will state that Darren may have overstated the case for them being salamanders. Both clades noted (scapherpetids and noterpetontids) are really difficult to place with any certainty, but what is pretty clear is that they’re not part of the salamander crown, and while a minority of morphological analyses have recovered them with some relationship with proteids, sirenids, and amphiumids, this topology is highly influenced by large-scale parallelism throughout caudates, and there are good molecular and morphological reasons for believing that these results are wrong, at least when it comes to the extant material. This problem is ultimately solvable for extant groups (research in progress which I was hinting at to David Marjanovic earlier) but may not be solvable for noterpetontids and scapherpetids, as the anatomical regions of interest are not represented for these taxa.

    Noterpetontids specifically are very bizarre, and, among other things, exhibit procoelous vertebrae and axial morphology that’s completely disjunct from what we see in any other salamander or stem-salamander. See: Rage et al., 1993, for noterpetontid morphology.

    Scapherpetids are to my knowledge entirely Laurasian, with most diversity restricted to Montana and Alberta.

    Relying on noterpetontids as your counterexample, when noterpetontids are a giant question mark that sits somewhere outside of the salamander crown, is probably not wise.

    The earliest crown salamander comes from the Pleistocene of North Africa. So.

    Link to this
  62. 62. ectodysplasin 2:04 pm 10/3/2013

    *earliest crown salamander from Gondwana, sorry.

    Link to this
  63. 63. ectodysplasin 2:06 pm 10/3/2013

    @Dartian:

    You were not specifying what (Linnaean) taxonomic level you were operating with; to the contrary, you even specifically listed a bunch of ‘families’ to make your point. Thus your statement, as you yourself worded it, was just factually incorrect, plain and simple (as there are other tetrapod families and orders with predominantly high-latitude distributions). If you don’t express yourself clearly, others will misunderstand you – and it is then your fault, not theirs.

    I was very clearly talking about salamanders as a whole, and then mentioned lower-level salamander diversity to clarify how that distribution plays out on a taxon-by-taxon basis. I am sorry that this was not clear to you.

    Link to this
  64. 64. ectodysplasin 2:13 pm 10/3/2013

    @vdinets:

    I’ll ignore isolated cases like olms and Korean lungless salamander for now.

    Well, remember, olms live in a very specific habitat (karst and/or epikarst) that would have been somewhat insulated from the glaciation that knocked out most European herp diversity. Surface-dwelling proteids were completely extirpated from Europe. This is pretty telling when it comes to understanding current European salamander diversity, or lack thereof.

    Link to this
  65. 65. ectodysplasin 2:25 pm 10/3/2013

    @Dartian:

    No, the Neotropical plethodontid clades originated long before the Pleistocene, suggesting a very long history in this region (Parra-Olea et al., 2004).

    Since you’re so familiar with the work of Parra-Olea and colleagues, then I’m sure you’ve read Wiens et al., 2007, who demonstrated that lower-elevation clades are more recent, and that higher elevation clades have a lower extinction rate and more ancient and stable diversity. So it’s pretty obvious that the cordillera was the primary colonization route when it comes to the Neotropics.

    Link to this
  66. 66. ectodysplasin 2:46 pm 10/3/2013

    @Dartian:

    and dismissed ecological explanations (specifically, interactions with fish). Now you’re saying that bowfins and gars were eliminated from the tropics because of ecological reasons (specifically, competition with teleosts). Why do you casually propose ecological reasons in some cases and then equally casually dismiss them in other cases?

    Gars and bowfins have an extensive and deep fossil record in Gondwana, but Gondwanan taxa eventually go extinct and are replaced by teleosts that fill the same niches. Whether that’s direct competition or progressive extinction with replacement is probably not something that can be directly tested, but the pattern is that holosteans were a diverse and significant component of the Gondwanan ichthyofauna and then disappeared and were replaced by teleosts. Same thing happens to other “ancient” fish clades in Laurasia (e.g. lungfishes, which disappear in Laurentia sometime in the Cretaceous).

    Salamanders simply don’t make it into Gondwana at all. They have no fossil record there. Extant lineages in Gondwana are very recent. Colonization is accomplished by only a handful of closely related lineages, along a single colonization route. This is a colonization route that lacks abundant standing water even if it retains humidity and precipitation, which excludes use of this route by most salamanders, including most plethodontids.

    In addition, the barrier that this colonization route seems to traverse is not the tropics per se, but rather the arid belts at the horse latitudes. Frogs seem to be able to handle aridity. Salamanders seem unable to. Given that these aridity belts are a function of atmospheric circulation, they were likely present throughout the Mesozoic as well, which could explain why most salamander diversity stays north of the horse latitudes.

    Link to this
  67. 67. vdinets 3:58 pm 10/3/2013

    ectodysplasin (#64): the situation in Europe seems to be fairly understandable. What interests me is why there is so much difference between China and North America. They were very similar at some point, and even today forests of Ussuriland and Shenandoah look strikingly similar, all the way to minor details, like tiny flies getting into your eyes, Adiantum ferns dominating patches of the forest floor, or Saturniid moths emerging in the fall. But some groups have huge diversity in one place and zero or almost zero in the other. In some cases you can explain it by postulating one place (usually China) as being the ancient center of origin, but it probably wouldn’t work with salamanders.

    #66: OK, but why are gars so successful in North America today? They live in areas with some of the highest freshwater Teleost diversity outside the tropics, and overlap with pikes a lot (I can’t think of any other fish in subtropical Asia or North America that would compete with them). In some places (such as much of Florida) they are probably the most commonly seen freshwater fishes. In the South you could explain it by the fact that alligators don’t usually eat them, but what about the northern part of the range? And bowfin seems to be doing really well, too.

    Link to this
  68. 68. ectodysplasin 8:39 pm 10/3/2013

    @vdinets:

    #66: OK, but why are gars so successful in North America today? They live in areas with some of the highest freshwater Teleost diversity outside the tropics, and overlap with pikes a lot (I can’t think of any other fish in subtropical Asia or North America that would compete with them). In some places (such as much of Florida) they are probably the most commonly seen freshwater fishes. In the South you could explain it by the fact that alligators don’t usually eat them, but what about the northern part of the range? And bowfin seems to be doing really well, too.

    You might want to think about how gars handle hypoxic, stagnant water, vs how well most teleosts handle the same types of environments.

    Link to this
  69. 69. vdinets 12:31 am 10/4/2013

    Well, they can’t be THAT much better at it, considering that they feed on teleosts and can’t live without them. Also, alligator gars prefer slow rivers and shallow brackish lagoons rather than stagnant ponds.

    Link to this
  70. 70. Gigantala 5:53 am 10/4/2013

    Considering champsosaurus appear to have occupied a very gar-like ecological niche, I wouldn’t put it that competition is simply unrelated to how gar distribution progressed across time. Frankly, I’d rather expect gharials to have had more impact than teleosts.

    Link to this
  71. 71. Dartian 6:14 am 10/4/2013

    Heteromeles:
    the Himalayas kept Chinese salamanders from migrating south into Vietnam

    Actually no. As Vlad said, there are salamanders in Vietnam (e.g., Paramesotriton and Tylototriton and, for that matter, also in Laos.

    ectodysplasin:
    Darren may have overstated the case for them being salamanders. Both clades noted (scapherpetids and noterpetontids) are really difficult to place with any certainty, but what is pretty clear is that they’re not part of the salamander crown, and while a minority of morphological analyses have recovered them with some relationship with proteids, sirenids, and amphiumids, this topology is highly influenced by large-scale parallelism throughout caudates, and there are good molecular and morphological reasons for believing that these results are wrong, at least when it comes to the extant material.

    Fair enough. Thanks for the clarification.

    I am sorry that this was not clear to you.

    It’s OK, just be more careful next time. ;)

    Since you’re so familiar with the work of Parra-Olea and colleagues, then I’m sure you’ve read Wiens et al., 2007

    I have, yes. Both papers say essentially the same thing – unsurprisingly, considering that they share no fewer than three authors between them – so I thought that citing one would be sufficient. But for the sake of completeness, by all means let’s cite that other one in full too:
    Wiens, J.J., Parra-Olea, G., García-París, M. & Wake, D.B. 2007. Phylogenetic history underlies elevational biodiversity patterns in tropical salamanders. Proceedings of the Royal Society B 274, 919-928.

    it’s pretty obvious that the cordillera was the primary colonization route when it comes to the Neotropics.

    Yes – but what made you think that I was disagreeing with that? Vlad was wondering about for how long salamanders have been present in the Neotropics (specifically, Central America). Both of those two above-mentioned studies report considerable molecular differences between various Neotropical salamander clades. Those results suggest that some of these plethodontid lineages diverged many millions of years ago, long before the Pleistocene (perhaps in the Miocene). And it’s pretty safe to assume that most or all of these clades diverged in situ in Central America (alternatively, they independently invaded Mesoamerica from North America, but that’s not a very parsimonious assumption).

    Link to this
  72. 72. naishd 6:31 am 10/4/2013

    Very much enjoying the extensive commenting that’s going on here – thanks indeed, sorry I’m not chipping in… too swamped with a major book project that’s eating up all my time.

    On overstating the salamanderyness of noterpetontids, scapherpetids and so on — I confess that, until now, I hadn’t really appreciated that there were doubts. I can’t say that this is evident from the literature (as noted in the article, and by ectodysplasin in comments above, these groups are said or inferred to be nested deep within crown-salamanders, sometimes being regarded as stem-members of extant lineages.. cf. noterpetontids vs sirenids).

    And, funnily enough, noterpetontids have been the subject of quite a bit of discussion at conferences lately (for reasons that might become evident in the literature some time soon) — none of the people I spoke to (one of whom is a salamander specialist) expressed doubts about placement of this group within Caudata.

    Anyway, good to know this stuff. We’ll get there eventually.

    Darren

    Link to this
  73. 73. David Marjanović 6:55 am 10/4/2013

    also appear to be photosynthetic, at least as embryos

    …That seemed vaguely familiar, but I had managed to forget about it! Thanks for reminding me! :-)

    Can’t you just cite the digimorph data?

    …Oh. Thanks! I’ve been meaning for ages to check if Digimorph had any salamanders or was limited to amniotes, but I kept forgetting! Of course I can cite it. :-)

    We’re talking about a lineage that dates back at least as far as the early Triassic

    (That’s total-group salamanders, as judged from the fact that the stem-frogs Triadobatrachus and Czatkobatrachus are that old. The known stem-salamanders are all Middle to Late Jurassic and Eurasian.)

    So what about those Mesozoic South American and African sirenid fossils that Darren mentioned? Are you suggesting that they’ve been misidentified?

    We are talking about isolated vertebrae here…

    Both clades noted (scapherpetids and noterpetontids)

    Noterpetids then, logically :-)

    (Prevailing usage can overturn this. But there’s almost no usage of that name at all.)

    are really difficult to place with any certainty, but what is pretty clear is that they’re not part of the salamander crown,

    Wait, how is that clear?

    and while a minority of morphological analyses have recovered them with some relationship with proteids, sirenids, and amphiumids

    Have you seen a phylogenetic analysis with a noterpetid in it? I haven’t. I think I’ve seen a few with scapherpetids and/or batrachosauroidids, but they were all the kind of analysis that lumps all neotenic salamanders together. :-( Yay for people glossing over correlated characters!

    Scapherpetids are to my knowledge entirely Laurasian, with most diversity restricted to Montana and Alberta.

    Yep. There aren’t any known from Asia (Eoscapherpeton has turned out to be on the cryptobranchid side of things), and IIRC not even from Europe. There are batrachosauroidids from Europe… but I think none from Asia either.

    Surface-dwelling proteids were completely extirpated from Europe.

    That’s what everybody believed till Proteus anguinus parkelj was discovered! It does live in a glacial refuge, though.

    Link to this
  74. 74. vdinets 10:26 am 10/4/2013

    David: could P. a. parkelj be a post-glacial re-invasion? It’s so local and doesn’t seem to differ much…

    Link to this
  75. 75. David Marjanović 10:45 am 10/4/2013

    Back to the article:

    olms have been covered on Tet Zoo before: see the links below

    It’s not there! HALP! :-)

    Link to this
  76. 76. ectodysplasin 12:33 pm 10/4/2013

    @David;

    (That’s total-group salamanders, as judged from the fact that the stem-frogs Triadobatrachus and Czatkobatrachus are that old. The known stem-salamanders are all Middle to Late Jurassic and Eurasian.)

    Yes. The salamander stem necessarily dates back as far as the frog stem, unless we have our tree wrong.

    are really difficult to place with any certainty, but what is pretty clear is that they’re not part of the salamander crown,

    Wait, how is that clear?

    Went back and read Rage et al., and you’re right, they propose that Noterpeton plus another procoelous form from Niger might represent a parallel Gondwanan diversification to Urodela, but provide no justification besides the fact that the procoelous vertebrae are bizarre (which they are).

    Rage et al. (2003) mention a posterolateral branching of the neural spine, which is what Evans then suggests might make Noterpeton a sirenid. Holman pushes this harder, even though the material is pretty inconclusive. There’s a whole lot of other animals that could represent. Without more complete material, it’s an interesting sidenote, but nothing I’d hang a paleobiogeographic or phylogenetic hypothesis on.

    Have you seen a phylogenetic analysis with a noterpetid in it? I haven’t. I think I’ve seen a few with scapherpetids and/or batrachosauroidids, but they were all the kind of analysis that lumps all neotenic salamanders together. :-( Yay for people glossing over correlated characters!

    Thinking Scaphs and Batrachs. And yes, they tend to lump all hyperelongate salamandes together. I’m not 100% convinced that neoteny is the only problem there, though.

    Link to this
  77. 77. ectodysplasin 12:41 pm 10/4/2013

    @David:

    That’s what everybody believed till Proteus anguinus parkelj was discovered! It does live in a glacial refuge, though.

    P. anguinus parkerlj still lives entirely in karstic environments. It simply hasn’t lost pigment or eyes (yet).

    Link to this
  78. 78. ectodysplasin 2:27 pm 10/4/2013

    @llewely:

    ” Bizarrely, salamanders have disproportionately large amounts of DNA.”

    Bizarrely?

    Is there actually any evidence for a substantial relationship between skeletal complexity and amount of DNA?

    This has been begging me for a response for days but I’ve been busy and thus have been responding in short bursts.

    But!

    The answer is: yes, but it’s complicated. Genome duplications have been suggested to be responsible for increased complexity, because paralogs (different duplicates of the same gene) can specialize, leading to lower developmental integration of morphological units.

    On the other hand, very large genomes have been suggested to have a role in paedomorphosis in some taxa, including salamanders e.g. Roth et al., 1997. The argument is that large genomes mean large cells mean slower development times and decreased tissue complexity. Is this the case? Dunno, but it makes for an interesting story, and we can look at parallels (e.g. modern lungfishes) which show similar correlation between genome size and paedomorphosis.

    Link to this
  79. 79. David Marjanović 11:28 am 10/5/2013

    P. anguinus parke[...]lj still lives entirely in karstic environments.

    …Yeah, but not underground, where it’d be much more protected from an ice age.

    Link to this
  80. 80. vdinets 8:08 pm 10/5/2013

    Would be really cool if someone discovered a neotenic frog… Just imagine those blind, white, translucent tadpoles lurking in the darkness of the cave, or amphiuma-size monsters terrorizing the Deep South with their habit of tickling swimmers to death…

    Link to this
  81. 81. David Marjanović 5:15 am 10/6/2013

    In frogs, sexual maturity is part of the later stages of metamorphosis. Apparently it’s not possible to make it independent again.

    This must be why even completely aquatic frogs (pipids, say) have a complete metamorphosis from a tail-propelled to a hindlimb-propelled swimmer in which they close all their gill slits.

    Link to this
  82. 82. naishd 7:50 am 10/6/2013

    I agree with David — anurans seemingly ‘can’t’ evolve a paedomorphic form (even though there are sometimes some surreal, naturally occurring mutants among assorted frog species). I still like the idea that it’s the selection pressures acting on tadpoles that have shaped the evolution of the adult anuran body form… Not saying I support it, but I like it.

    Back to salamanders.. a link to the Tet Zoo olm article was missing from the list above. Have now added it.

    Darren

    Link to this
  83. 83. ectodysplasin 4:39 pm 10/6/2013

    @David:

    …Yeah, but not underground, where it’d be much more protected from an ice age.

    The springs which black Proteus have been collected from are all outlets of a common underground river system. So, probably still a stygibiont, even though it’s not white and eyeless.

    Link to this
  84. 84. David Marjanović 7:37 am 10/7/2013

    Back to salamanders.. a link to the Tet Zoo olm article was missing from the list above. Have now added it.

    Thanks, I needed to read it again. :-)

    Link to this
  85. 85. Yodelling Cyclist 12:34 pm 10/30/2013

    On the subject of the strangely large genomes, I’ve wondered if this could be tied to what drug-discovery chemists call cryptic natural products. In their case, the idea is that when an organism is cultured in the lab, under “benign” conditions, only a limited number of proteins are expressed, but when the same organism is stressed (by toxins, starvation, heat, light, whatever) new pathways are activated within the cells and novel, previously unrecognised, proteins/metabolic products in general are generated in order to cope with the changed conditions. Genetics is very much not my thing, but I was wondering if the enlarged genomes of salamanders and lungfish might be linked to their unusual amphibious capabilities: over the course of their natural life cycle, even under ideal conditions, most salamanders (or indeed lungfish) can expect to switch between different respiration mechanisms, different ambient humidity (i.e. in a pond or in dry air) very different temperature environments etc. in addition to all the “usual” back processes up that such an animal may require (to compensate for starvation, exhaustion, hypoxia, whatever). Salamanders also require all the molecular machinery to effect metamorphosis. The reason why other taxa with more conventional lifestyles (i.e. those of us animals who are born without a metamorphosis requirement and stay for our whole lives on land, at sea, wherever) don’t have such a large genome providing little used, but handy, biochemistry is because beyond a certain genome size cell division becomes more difficult than it’s worth. It’s like the giant Swiss army pen knife problem: it’s great to have all the tools, but if you’re travelling light you really don’t need, and are never going to use, the integrated awl.

    Do frogs pack a lot of DNA?

    Link to this
  86. 86. David Marjanović 4:22 pm 11/5/2013

    I was wondering if the enlarged genomes of salamanders and lungfish might be linked to their unusual amphibious capabilities

    No. Salamanders and lungfish do not have an unusual amount of genes, they have an unusually large amount of junk DNA, of trash that doesn’t code for anything and doesn’t do anything except inflate the cells.

    Do frogs pack a lot of DNA?

    Nope. Many do have more DNA than humans (while others have much less!), but all have much less than salamanders or lungfish. Unfortunately I can’t link to the results directly, but start searching here.

    Link to this

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