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Australia, land of dragons (by which I mean: agamids) (part I)

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


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Agamids are a widespread, diverse iguanian lizard group that I have a special fondness for and consequently have featured several times on Tet Zoo (see links below). Of course, I’ve never featured them enough, nor discussed or even mentioned whole groups of species that really should get adequate coverage here. In a recent article I discussed several taxa within the Australian earless dragon clade Tympanocryptis. Today, I want to expand the discussion somewhat by looking at Australian agamids more generally.

Clockwise from the upper left: Pogona, Chlamydosaurus, Moloch. Images by Tony Gamble (Pogona) and (c) Stephen Zozaya, used with permission.

There are about 70 agamid species in Australia (though maybe much more), all belonging to the clade Amphibolurinae and vernacularly termed amphibolurines or amphiboluroids or just dragons (waitaminute… isn’t that term in use someplace else?). This group is not endemic to Australia since species also occur in tropical eastern Asia and New Guinea as well. As you’d predict, species also occur on various of the islands between Australia and the Asian mainland.

Amphibolurines include long-tailed, superficially iguana-like rainforest and woodland forms, short-snouted, spiny-bodied animals of dry woodlands and deserts, and a large number of slender, highly gracile semi-arboreal and desert-dwelling specialists. Then there are weirdos like the pebble-mimics, the ant-eaters that are covered in thorn-like spines, and so on. The majority are predators of arthropods. The larger species, however, are capable of tackling and eating other reptiles and even nestling birds and small mammals, and some are omnivorous and will eat flowers and fruits.

Frilled dragon of the especially dark sort seen in Cape York Peninsula: I love the fact that you can see the large caniniform teeth in this shot. Image (c) Stephen Zozaya, used with permission.

Several things make this lizard radiation especially fascinating. For one, it includes a number of morphologically and behaviourally bizarre animals. Perhaps the most familiar is the Frilled lizard, Frilled dragon or Frillynecked dragon Chlamydosaurus kingii, a highly variable, mostly insectivorous agamid that reaches 85 cm in total length and is predominantly arboreal. Its terrestrial bipedal behaviour is well known: TV documentaries often show these lizards sprinting bipedally away from menacing camera-holding humans, but they’re also known to engage in peculiar, prancing bipedal locomotion as their normal method of moving at ground level (Shine & Lambeck 1989). That’s right – this is a (faculatively) bipedal lizard.

The famous frills of these lizards – controlled by massively enlarged hyoid bones and borne on a proportionally long neck (Shine 1990) – are used by the males in dominance battles. Recent work shows that the reddishness of the frill is controlled by the presence of caretenoids, with males judging the quality of opponents based on this reddishness (Hamilton et al. 2013). We know that the frill is used to intimidate would-be predators, but it seems that sexual selection has also contributed to its evolution (Shine 1990). Somebody now needs to test female preference as goes frill ornamentation in these animals (Hamilton et al. 2013).

Amazing little Moloch - this one was photographed at Uluru (photo by Adam Yates, used with permission). Note the rounded pseudo-head at the back of the real one.

Moving on — there’s also the Thorny devil Moloch horridus, sometimes just called the Moloch, a tiny, slow-moving, rather sedentary, spiky, desert-dwelling, myrmecophagous (= ant-eating) amphibolurine that’s strongly convergent with the horned lizard (Phrynosoma) of North America. Thanks mostly to work by Eric Pianka and colleagues, we know a fair bit about the ecology, behaviour and life cycle of this remarkable lizard. Females are bigger than males (a peculiar feature for a lizard) and there are indications that individuals are reasonably long-lived, perhaps surviving into their third decades (remember that this is an animal less than 20 cm long). Females construct a burrow with a large open chamber at the end (about 8 x 13 x 15 cm in size) and the hatchlings apparently eat their eggshells. Both features are also very unusual (if not unique) within lizards (Pianka & Vitt 2003). All populations of Moloch are currently regarded as belonging to the same single species. However, variation in foot anatomy has at times led to the suggestion that there might actually be a set of cryptic species here: a hypothesis that awaits an analysis of variation within Moloch across its range.

Moloch: young, novel and deeply nested, or old, early and independent?

Substantially simplified amphibolurine cladogram, mostly based on the topology shown in Pyron et al. (2013). Chinese water dragon image by Marcel Burkhard, licensed under Creative Commons Attribution-Share Alike 2.0 Germany license. Other images by Adam Yates (Gowidon), Tony Gamble (Intellagama and Pogona), and Stephen Zozaya (the remainder), used with permission.

Despite its extreme weirdness, Moloch has been argued by some authors to be a geologically young novelty, deeply nested within the amphibolurine radiation, and specifically within the clade of dry-adapted lineages. A close affinity with the forest and angle-headed dragons (Hypsilurus) has been supported in some studies (Macey et al. 2000, Hugall et al. 2008) and Pyron et al. (2013) even found both Moloch and Chelosania brunnea (the unique Ring-tailed dragon or Chameleon dragon) to be nested within Hypsilurus. Rather than finding Moloch to be a recently evolved ‘core member’ of Amphibolurinae, Hugall et al. (2008) and Pyron et al. (2013) found Moloch, Hypsilurus and Chelosania to belong outside the clade that contains the majority of amphibolurine lineages.

This was also recently supported by Hutchinson & Hutchinson (2011) who showed that Moloch has the 12 chromosome pairs thought primitive for Agamidae. This makes it likely that it’s probably outside the main amphibolurine radiation, the members of which are united by the presence of 10 chromosome pairs. Chelosania also has the primitive 12 chromosome pairs. If Hugall et al. (2008), Hutchinson & Hutchinson (2011) and Pyron et al. (2013) are right, Moloch evidently adapted to desert conditions all on its own, very much independently from the dry-adapted ‘core’ amphibolurines. Intriguingly, Chelosania is an animal of dry woodlands and not rainforest, so it might also be part of an early movement into drier habitats (Hugall et al. 2008).

Forest dragons and angle-headed dragons: there are more than you think

Beautiful image of Boyd's forest dragon: (c) Stephen Zozaya, used with permission.

Boyd's forest dragon doing the vertical clinging thing. Image (c) Stephen Zozaya, used with permission.

I just mentioned Hypsilurus. This is one of those fantastically ornate iguanian taxa. Boyd’s forest dragon H. boydii, one of the biggest and most ornate of the group, has enlarged cheek plates, tall nuchal and dorsal crests topped with curved, laterally compressed spines, and a giant dewlap, also lined with large spines. If you know the literature on Australian reptiles, you’ll likely think of Hypsilurus as a group that contains just two species: the second being the Southern angle-headed dragon H. spinipes. In fact, there are about 20 of the things, four of which (H. hikidanus, H. magnus, H. ornatus and H. tenuicephalus) were named in 2006 (Manthey & Denzer 2006). These inhabit New Guinea, the Aru Islands, the Bismarck Archipelago, the Solomon Islands and various of the small surrounding islands.

Are there more than just two species in Australia? H. longii has been reported from Cape York Peninsula but this is considered doubtful by some authors. And a very surprising record of the genus is a single photographic record – said to depict H. dilophus – from way out to the west in Sulawesi (Manthey & Denzer 2006). If this record is valid, it suggests the presence of cryptic or extinct populations that must have occurred in between those on and around New Guinea and those on and around Sulawesi. The historical taxonomy of the Hypsilurus species is a fairly complex nightmare, by the way: they have been extensively confused with (and often considered congeneric or synonymous with) the draconine agamid Gonocephalus.

Dissolution of the water dragons

Not an Australian: the much-maligned Chinese water dragon. Like many 'familiar' animals, there's very little data on its anatomy, ecology and behaviour in the wild. Image by Marcel Burkhard, licensed under Creative Commons Attribution-Share Alike 2.0 Germany license.

Excluding that weird, wayward record of Hypsilurus, the only amphibolurine outside of Australasia and its surrounding islands is Physignathus, the Green or Chinese water dragon [adjacent image by Marcel Burkhard]. Typically, two extant Physignathus species have been recognised: the superficially iguana-like Eastern or Australian water dragon P. lesueurii of Australia’s Pacific seaboard and southern New Guinea, and the Green or Chinese water dragon P. cocincinus, familiar to anyone who’s ever walked into a pet shop that sells reptiles.

While both are superficially alike and both lounge around on branches that overhang water (and swim capably when the need arises*), they look extremely different in detail. Are these two really close relatives? Actually, they never group together in phylogenetic studies, the Eastern water dragon being closer to other amphibolurines than is the Chinese water dragon (Honda et al. 2000, Macey et al. 2000, Hugall & Lee 2004, Hugall et al. 2008, Townsend et al. 2011, Pyron et al. 2013). Since the Chinese water dragon is the type species for the name Physignathus (Georges Cuvier came up with the binomial Physignathus cocincinus in 1829), the Eastern water dragon needs a new name. After several false starts, it has been argued (Amey et al. 2012) that a generic name proposed by Wells & Wellington (1985) is the one we have to stick with. Thus the Eastern water dragon is now Intellagama lesueurii. No etymology was ever provided for the name Intellagama: I wonder what it means?

* The Eastern water dragon is even able to remain submerged for a considerable period – an hour or more, apparently. It exhibits a diving response – its heart rate slowing and rate of oxygen consumption decreasing – and is also able to release CO2 cutaneously (Pianka & Vitt 2003). Image of swimming water dragon below by D. Gordon E. Robertson.

As suggested by the name, water dragons are great swimmers (and divers). Here's the sort of thing that keeps palaeontologists awake at night: would we know this from their bones alone? Image by D. Gordon E. Robertson, licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

There are two main competing phylogenetic hypotheses regarding the position of water dragons relative to other amphibolurines: each implies a different biogeographical scenario for the group. In some studies, the Chinese water dragon is recovered as the sister-taxon to remaining amphibolurines (Macey et al. 2000, Hugall & Lee 2004, Hugall et al. 2008, Pyron et al. 2013) – a topology which suggests that amphibolurines originated in mainland Asia and that all members of the Australasian clade descend from a single ancestor that invaded this region after migrating away from Asia (strengthening this scenario is the fact that all non-amphibolurine agamids are Eurasian or African). In other studies, the species is nested within Amphibolurinae, being closer to Chlamydosaurus and Pogona (a genus we’ll look at in part II) than is Lophognathus (Honda et al. 2000). If this is right, Physignathus is of Australian ancestry and members of its lineage moved away at some point, eventually getting as far as mainland Asia. The first scenario is looking more likely.

Eastern water dragon; image by Tony Gamble, used with permission.

Intellagama is known from reasonably abundant remains to have been present in the Miocene of Queensland (where its jaws and other bones are preserved at Riversleigh). The fossils – identified by Covacevich et al. (1990) as Physignathus sp. (of course, now this should be Intellagama sp.) – indicate that members of this lineage have therefore been in existence for something like 20 million years. [UPDATE: see comment # 66 below (by John Scanlon). Those Riversleigh fossils may not belong to Intellagama at all.] Phylogenies indicate that Intellagama is outside the clade that contains Ctenophorus and the dry-adapted ‘core’ amphibolurines, so its antiquity is consistent with the idea that most of the amphibolurine radiation occurred some time after the start of the Miocene.

‘Ta ta dragons’: Lophognathus and… Gowidon?

Intellagama is somewhat similar in overall appearance to the several Lophognathus dragons – in fact, both have been considered synonymous by some authors in the recent past*, and at least some species of Lophognathus are sometimes called water dragons too. An alternative vernacular name – Ta ta dragons – refers to their habit of waving their limbs after moving on hot surfaces (‘Ta ta’ is a colloquial term for ‘goodbye’ in some parts of the world). Seeing as I’d like to be able to distinguish these animals from other Aussie dragons, I wonder if we should stick with this term. What the hell; it’s what I’m going to do here. Ta ta dragons occur widely across the upper two-third or so of Australia. L. temporalis inhabits both coastal northern Australia as well as New Guinea while L. maculilabris is unique to the Tanimbar Islands (or Timor Laut) of the Lesser Sundas. Wait a minute… this means it’s another non-Australasian amphibolurine, right?

* Lophognathus was also long considered synonymous with Amphibolorus but, then, so were most other amphibolurines, so this doesn’t mean much.

Gilbert's dragon (sensu lato!), photographed at Mataranka, NT. Image by Adam Yates, used with permission.

Of the several species, the greyish or reddish-brown Gilbert’s dragon L. gilberti is comparatively short-snouted and hence looks more Intellagama-like than some of the others. However, as is the case with several of the agamids discussed here, L. gilberti seems to be a species complex (Cogger 2000. Melville et al. 2011), and molecular results indicate that some of the populations conventionally included in this species are not close relatives – in fact, one of them is an unnamed taxon within Amphibolurus (another genus we’ll look at in part II). Are ta ta dragons really close to the Physignathus water dragons? The phylogenies say no (Honda et al. 2000, Hugall et al. 2008, Melville et al. 2011, Pyron et al. 2013).

Lonchognathus (or Gowidon) longirostris in breeding condition, photographed at Alice Springs. Image by Adam Yates, used with permission. If you don't stop at this image and think (or say) "Wow", you're dead inside. And maybe outside too, I dunno.

And are all of the ta ta dragons close relatives anyway? Gilbert’s dragon looks different from the more boldly striped, generally longer-tailed, longer-snouted species and these differences and others led Wells & Wellington (1983) to propose the new genus Gowidon for L. longirostris and others. Support for this view comes from the fact that Melville et al. (2011) found Lophognathus as most usually conceived to be polyphyletic, with L. longirostris and L. temporalis both grouping as distinct lineages close to a Rankinia + Pogona + Tympanocryptis clade, and L. burnsi and L. gilberti being close to Amphibolurus (and not, incidentally, closer to each other than they were to the included Amphibolurus species) (see also Pyron et al. 2013). A fair bit of work is needed to sort out the phylogeny and systematics of these animals.

We’re not done yet – there’s lot more to say. So stay tuned for part II, coming soon. And I need to finish by saying thank you to the several wonderful individuals who let me use their photos, and thus made this article possible. Thank you Adam Yates (who now blogs at A Fragment of Gondwana), Stephen Zozaya (check out his blog: Saurian Obsessions!) and Tony Gamble. This article literally would not have happened without their help.

For previous Tet Zoo articles on agamids and other iguanian lizards, see…

Refs – -

Amey, A. P., Couper, P. J. & Shea, G. M. 2012. Intellagama lesueurii (Gray, 1831), the correct binomial combination for the Australian Eastern Water Dragon (Sauria, Agamidae). Zootaxa 3390, 65-67.

Covacevich, J. A., Couper, P., Molnar, R. E., Witten, G. & Young, W. 1990. Miocene dragons from Riversleigh: new data on the history of the family Agamidae (Reptilia: Squamata) in Australia. Memoirs of the Queensland Museum 29, 339-360.

Cogger, H. G. 2000. Reptiles and Amphibians of Australia. Reed New Holland, Sydney.

Hamilton, D. G., Whiting, M. J. & Pryke, S. R. 2013. Fiery frills: carotenoid-based coloration predicts contest success in frillneck lizards. Behavioral Ecology 24, 1138-1149.

Honda, M., Ota, H., Kobayashi, M., Nabhitanhata, J., Yong, H.-S., Sengoku, S. & Hikida, T. 2000. Phylogenetic relationships of the family Agamidae (Reptilia: Iguania) inferred from mitochondrial DNA sequences. Zoological Science 17, 527-537.

Hugall, A. F., Foster, R., Hutchinson, M. & Lee, M. S. Y. 2008. Phylogeny of Australasian agamid lizards based on nuclear and mitochondrial genes: implications for morphological evolution and biogeography. Biological Journal of the Linnean Society 93, 343-358.

- . & Lee, M. S. Y. 2004. Molecular claims of Gondwanan age for Australian agamid lizards are untenable. Molecular Biology and Evolution 21, 2102-2110.

Hutchinson, M. N. & Hutchinson, R. G. 2011. Karyotypes of Moloch and Chelosania (Squamata: Acrodonta). Journal of Herpetology 45, 216-218.

Macey, J. R., Schulte, J. A., Larson, A., Ananjeva, N. B., Wang, Y., Pethiyagoda, R., Rastegar-Pouyani, N. & Papenfuss, T. J. 2000. Evaluating trans-Tethyan migration: an example using acrodont lizard phylogenetics. Systematic Biology 49, 233-256.

Manthey, U. & Denzer, W. 2006. A revision of the Melanesian-Australian angle head lizards of the genus Hypsilurus (Sauria: Agamidae: Amphibolurinae), with description of four new species and one new subspecies. Hamadryad 30, 1-40.

Melville, J., Ritchie, E. G., Chapple, S. N. J., Glor, R. E. & Schulte, J. A. 2011. Evolutionary origins and diversification of dragon lizards in Australia’s tropical savannas. Molecular Phylogenetics and Evolution 58, 257-270.

Pianka, E. R. & Vitt, L. J. 2003. Lizards: Windows the Evolution of Diversity. University of California Press, Berkeley.

Pyron, R. A., Burbrink, F. T. & Wiens, J. J. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 2013, 13:93 doi:10.1186/1471-2148-13-93

Shine, R. 1990. Function and evolution of the frill of the frillneck lizard, Chlamydosaurus kingii (Sauria: Agamidae). Biological Journal of the Linnean Society 40, 11-20.

Shine, R. & Lambeck, R. 1989. Ecology of Frillneck lizards in tropical Australia. Australian Wildlife 16, 491-500.

Townsend, T. M., Mulcahy, D. G., Noonan, B. P., Sites, J. W., Kuczynski, C. A., Wiens, J. J. & Reeder, T. W. 2011. Phylogeny of iguanian lizards inferred from 29 nuclear loci, and a comparison of concatenated and species-tree approaches for an ancient, rapid radiation. Molecular Phylogenetics and Evolution 61, 363-380.

Wells, R. W. & Wellington, C. R. 1985. A classification of the Amphibia and Reptilia of Australia. Australian Journal of Herpetology, Suppl. Ser. 1, 1-61.

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. David Marjanović 6:10 pm 01/16/2014

    is also able to release CO2 cutaneously

    Not bad… not bad at all.

    Here’s the sort of thing that keeps palaeontologists awake at night: would we know this from their bones alone?

    Do we know their bones? Has the skeleton ever been described?

    Just today I had to cite a palaeontological paper for a skeletal polymorphism (presence and absence of a process on a bone) in an extant, widespread European species.

    Link to this
  2. 2. naishd 7:07 pm 01/16/2014

    It’s funny you say that (about data on the osteology). I was reading up on Physignathus — the really, really familiar green lizard that is seemingly ubiquitous as a pet and zoo exhibit — and the article said something like “No descriptive work exists beyond that of Cuvier 1829″ (paraphrased and technically wrong, but something like that). I’ll try and find the exact quote. Your point is well made.

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  3. 3. ectodysplasin 7:19 pm 01/16/2014

    Even singular “important” taxa are underdescribed in terms of morphology. Little surprise that morphology of taxa in speciose groups is essentially undescribed.

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  4. 4. Mark Hutchinson 7:40 pm 01/16/2014

    Hi Darren – Thanks for putting up a great review of one of my favorite animal groups. I like your ‘wake in fright’ type comment about aquatic habits of water dragons. Animals with the sort of general-purpose skeletons that lizards have don’t reveal a lot about their habits or ecology from their bones and I sometimes wince when I see speculation about what some fossil lizard might have done ecologically or behaviorally. Amphibolurine genera have proven to be unstable in many cases, and it’s paradoxically due to both conservatism – a lack of divergence in body form in spite of long periods of evolutionary time going by (e.g. the Amphibolurus/Lophognathus/Gowidon mess), and plasticity – a rapid change in external appearance in the face of some selective pressure that leads to convergence (Rankinia diemensis and the Ctenophorus adelaidensis group) or strong divergence (e.g. Caimanops embedded within Diporiphora). Little rascals!
    PS. Long-nosed dragons are completely delightful. Of course.

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  5. 5. Mark Robinson 9:30 pm 01/16/2014

    A fascinating read as usual, Darren. You mention several common-names for Chlamydosaurus kingii but not the one that I hear most often here in Australia, which is “Frill-necked Lizard”.

    A second ‘Wow’ from me regarding the ability to release CO2 cutaneously. That’s up there with butt-breathing.

    I agree that bones alone will never tell the whole story – is there anything about a panda’s skeleton that would allow us to guess that it derives almost all of its nutritional and energetic requirements from bamboo?

    And thanks for not mentioning Hoser anywhere.

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  6. 6. ayates 11:03 pm 01/16/2014

    Cool post. Its great to see my photos put to good use, and thanks for giving my blog a plug.
    Interesting that Mark Hutchinson should describe the ta ta lizards as the ‘Amphibolurus/Lophognathus/Gowidon mess’ I used that exact same phrase in an email to Darren just two days ago. Either we think alike or there is no better way of labelling these lizards.
    Do you have any more info on ‘L.’ maculilabris? I would doubt that it is a genuine part of the australasian amphibolurine radiation but know of no evidence one way or the other.

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  7. 7. oldfarmermac 1:13 am 01/17/2014

    Thank you, Mr. Naish, on my own behalf and that of countless others for your highly enjoyable and educational work.

    Link to this
  8. 8. Dartian 3:18 am 01/17/2014

    Darren:
    dragons (waitaminute… isn’t that term in use someplace else?)

    Why, yes – there are flying dragons (i.e., Draco), and Komodo dragons, and then there are those seahorse relatives, the leafy sea dragons. Surely that’s what you had in mind? ;)

    Mark:
    the one that I hear most often here in Australia, which is “Frill-necked Lizard”

    That’s the vernacular name for this species that I’m most familiar with, too.

    Whatever it’s called, though, Chlamydosaurus has a bit of a reputation for being difficult to keep in captivity. Any herpetology enthusiasts out there who know if this is (still) the case?

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  9. 9. naishd 3:46 am 01/17/2014

    Thanks to all for comments so far. Yes, Frill-necked lizard should be added to that list, thanks. On the keeping of this species in captivity (comment # 8), I think that things have changed substantially since the 1970s – huge numbers of these lizards are now bred for the pet trade in Indonesia, and lots of collectors (and zoos and other collections) have them. I’m not sure, but I think that better understandings of nutritional demands have improved their longevity in captive conditions.

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  10. 10. Chabier G. 6:20 am 01/17/2014

    About “dragon” as a vernacular name for extant reptiles, “dragón” (in Aragonese) and “dragó” (in Catalan) are widespread common names for the humble Tarentola mauritanica in Aragón and Catalonia.

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  11. 11. David Marjanović 6:46 am 01/17/2014

    is there anything about a panda’s skeleton that would allow us to guess that it derives almost all of its nutritional and energetic requirements from bamboo?

    Its teeth show very clearly that it eats lots of tough plants; and then there are the famous “thumbs”.

    Link to this
  12. 12. ekocak 9:56 am 01/17/2014

    Frilled dragons are not considered difficult to keep any more. People didn’t used to understand the importance of UVA/UVB lighting for lizards, or even basic dietary requirements and I think that, along with their tendency to bash headlong into glass was what gained them that reputation. I see them in pet stores and at reptile shows pretty consistently these days, although not nearly as ubiquitous as bearded dragons.

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  13. 13. Yodelling Cyclist 10:20 am 01/17/2014

    Once again, good stuff.

    I, too, am amazed at CO2 release underwater. Anyone looked for cutaneous O2 uptake as in some turtles?

    Finally, in reference to the comments that lizards in general are rather conservative and also frequently convergent, are there any fears that molecular biology could spring nasty surprises? I recall a comment from a while ago (which was better phrased) which observed that in small mammal skeletal physiology it was often hard to capture or reproduce the genetics-derived phylogeny, and I believe I’m right in saying that similar things have been found for birds. I guess what am asking is, how secure are these phylogenies?

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  14. 14. Heteromeles 12:48 pm 01/17/2014

    Hmmmm. If small mammals, birds, and reptiles tend to be more generalized, in the sense that it’s hard to deduce their ecology and physiology from their skeletons or vice versa, perhaps this is a reason why small-bodied animals tend to survive mass extinctions? Perhaps it’s not just about their lesser resource needs, but about their an inherent ability to adapt to new conditions? Obviously this isn’t always true, but I wonder. Perhaps our inability to deduce function from form is, as the geeks say, a feature, rather than a bug.

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  15. 15. ectodysplasin 2:45 pm 01/17/2014

    @Yodelling,

    I recall a comment from a while ago (which was better phrased) which observed that in small mammal skeletal physiology it was often hard to capture or reproduce the genetics-derived phylogeny, and I believe I’m right in saying that similar things have been found for birds.

    This depends on character concept and ontology. Typically, character concepts with poor conceptual basis will result in trees overwhelmed by convergence. Ones with better conceptual basis tend not to be.

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  16. 16. ectodysplasin 6:11 pm 01/17/2014

    @Chabier;

    About “dragon” as a vernacular name for extant reptiles, “dragón” (in Aragonese) and “dragó” (in Catalan) are widespread common names for the humble Tarentola mauritanica in Aragón and Catalonia.

    Interestingly, the original Greek “dragon” probably referred to large pythonid snakes such as P. sebae and P. bivitattus and is essentially used in this manner by most classical authors.

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  17. 17. ChasCPeterson 9:02 pm 01/17/2014

    Another fine treatment of another cool clade.

    Cutaneous release of CO2 is not particularly unusual, especially under water. Submerged musk turtles (Sternotherus) lose about 30% of their total CO2 cutaneously. Even for terrestrial reptiles cutaneous CO2 loss can be an important route: 20% of total in Boa constrictor and 15% in Anolis carolinensis. It’s about 12% in bats!
    (These numbers are from one of my teaching slides; my books are currently more than 4000 km away so I cannot easily source them; sorry!)

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  18. 18. David Marjanović 9:14 am 01/18/2014

    Huh. For bats it makes sense because of the huge wing membrane…

    Finally, in reference to the comments that lizards in general are rather conservative and also frequently convergent, are there any fears that molecular biology could spring nasty surprises?

    Already happened, in squamate phylogeny as a whole. The traditional idea, based on analyses of small amounts of morphological data, is that Iguania (including agamas) is the sister-group to all the rest. Molecular analyses have turned this upside-down, finding Iguania very close to Anguimorpha (slowworms, monitors…) and to the snakes. In 2012, a large analysis of morphological data was done – and doubled down on the traditional idea. It’s suspicious, though, that this new analysis clusters the snakes with most or all other limbless squamates; that could mean there are correlated characters in this dataset.

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  19. 19. David Marjanović 9:16 am 01/18/2014

    and doubled down on the traditional idea

    Finding many previously overlooked characters that bolster it, I wanted to add.

    Link to this
  20. 20. Tayo Bethel 8:51 pm 01/18/2014

    Great article, as usual.

    Two questions. 1. Why is herbivory seemingly restricted to only two families of living squamates–Iguanidae and Agamidae? 2. way off topic–Which groups of squamates are most closely related to mosasaurs?

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  21. 21. David Marjanović 12:15 pm 01/19/2014

    1. Interestingly, both of these are iguanians; and interestingly, many other difficult diets – heavily armored and/or toxic beetles, for instance – are also more or less limited to iguanians. …However, other herbivorous squamates have existed. Look up Polyglyphanodontidae and Tianyusaurus.
    2. Good question. Probably the snakes + adriosaurs + dolichosaurs + pontosaurs + suchlike. Otherwise, some or all of Anguimorpha. The recent big morphological analysis found them outside a clade composed of most extant squamates, however.

    Link to this
  22. 22. Tayo Bethel 3:24 pm 01/19/2014

    @David Marjanović
    …So comparing them or their ancestors to living monitors issomewhat misleading then? Since they might not be particularly close to varanoids of any sort.

    Link to this
  23. 23. naishd 10:32 am 01/20/2014

    To follow on from what David just said, it’s been clear for a while that mosasaurs are nowhere near as close to monitors as popular books frequently make out. Even in morphology-based analyses that do find mosasaurs (= Mosasauroidea or Mosasauria) to be part of the same anguimorph clade as monitors and gila monsters, mosasaurs are outside of the crown-clade and hence some distance from monitors. There’s some discussion of this in the 2012 Tet Zoo article Monstersauria vs Goannasauria.

    Link to this
  24. 24. ectodysplasin 12:49 pm 01/20/2014

    @David;

    Already happened, in squamate phylogeny as a whole. The traditional idea, based on analyses of small amounts of morphological data, is that Iguania (including agamas) is the sister-group to all the rest. Molecular analyses have turned this upside-down, finding Iguania very close to Anguimorpha (slowworms, monitors…) and to the snakes. In 2012, a large analysis of morphological data was done – and doubled down on the traditional idea. It’s suspicious, though, that this new analysis clusters the snakes with most or all other limbless squamates; that could mean there are correlated characters in this dataset.

    The flip side is that some of the more “revolutionary” molecular results (e.g. polyphyletic Iguania) have turned out to be results of molecular convergence (see Castoe et al., 2008, for example) so in all likelihood we’re going to end up with a tree that retains some of the conventional morphological groupings, with some revisions (e.g. the more basal position of geckos). Both molecularly and morphologically, snakes seem to come out in anguimorphs more generally, which isn’t surprising and seems to be approaching a consensus, even if some workers still want to place them with dibamids and amphisbaenids.

    Link to this
  25. 25. ectodysplasin 12:52 pm 01/20/2014

    In addition, the convergences between snakes, dibamids, and amphisbaenids probably has more to do with adaptations for burrowing (where have we seen this before) than axial elongation per se. I suppose this has some implications for questions about whether snakes evolved in an aquatic or fossorial habitat.

    Link to this
  26. 26. Tayo Bethel 1:03 pm 01/20/2014

    @Naish:

    Thanks. Cladistics is fun :) BTW, where can i get an ebook copy of Varanoid Lizards of the World in Epub format?

    Link to this
  27. 27. Tayo Bethel 1:45 pm 01/20/2014

    Interestingly,some sources speculate that snakes evolved from mosasaurs.:) That’s like saying whales are the ancestors of some land mammals–in other words, highly improbable. Snakes, it seems,evolved from small fossorialsquamates.
    Another interesting observation: Most living fossorial squamates have reduced or absent front limbs, and the hind limbs, while absent in snakes, seem to have been lost long after the forelimbs.Mosasaurs,on the other hand, seem to have lost the hind limbs;the forelimbes are reduced in length but still quite functional. Hyperphalangae saw to that. So axial elongationseems to be convergent in mosasaursand snakes, much as limblessness is convergent in living squamates, including snakes.
    P.S. It seems that axial elongation is much more extreme in large snakes than inmosasaurs; 100 vertebrae for a large mosasaur vs. 300 fora large snake. Can anyone confirm this?

    Link to this
  28. 28. David Marjanović 7:47 am 01/21/2014

    Castoe et al., 2008

    Ref, please! :-)

    I suppose this has some implications for questions about whether snakes evolved in an aquatic or fossorial habitat.

    I’m about to read the paper on all the limbed snakes in the November issue of JVP.

    some sources speculate that snakes evolved from mosasaurs

    I’ve never seen a paper claim that. However, one of the two mainstream hypothesis is that snakes have indeed evolved from pretty large aquatic ancestors, not tiny burrowing ones, and are pretty closely related to the mosasaurs.

    Most living fossorial squamates have reduced or absent front limbs,

    Enter Bipes.

    and the hind limbs, while absent in snakes, seem to have been lost long after the forelimbs.

    Enter Adriosaurus microbrachis

    Mosasaurs,on the other hand, seem to have lost the hind limbs

    …Have you ever seen a mosasaur skeleton?

    It seems that axial elongation is much more extreme in large snakes than inmosasaurs; 100 vertebrae for a large mosasaur vs. 300 fora large snake. Can anyone confirm this?

    Of course. I don’t think there’s any vertebrate that retains all four limbs but has more than 100 presacral vertebrae. Brachydectes elongatus, as it’s currently called, has tiny limbs and 95 presacrals.

    Link to this
  29. 29. Tayo Bethel 11:11 am 01/21/2014

    @David:

    This is why i come to TetZoo (smile) Nope, I’ve never seen a mosasaur skeleton. … So Mosasaurs did have hind limbs?

    The mainstream hypothesis about snakes evolving from aquatic ancestors … hasanyone presented any evidence for or against? To me it still seems unlikely … where are all the fossil aquatic snakes? Why,if snakes evolved from aquatic ancestors, are there few primitive snakes that are aquatic? Questions, questions …

    P.S. I’m of the opinion that tiny size in living fossorial snakes is a derived, not a “primitive”trait. Admittedly, the fossil record can be very selective, but how many fossil snakes are less than medium-sized?

    Link to this
  30. 30. David Marjanović 11:54 am 01/21/2014

    So Mosasaurs did have hind limbs?

    Yes, and they’re routinely the size of the forelimbs! Why don’t you simply go to http://images.google.com/ and search for “mosasaur”? It’s not like it’s some kind of secret, you know! :-)

    The mainstream hypothesis about snakes evolving from aquatic ancestors …

    It’s one of two about equally mainstream hypotheses.

    hasanyone presented any evidence for or against?

    Lots of both! It’s been a hot topic in the scientific literature for the last 20 years! :-)

    where are all the fossil aquatic snakes?

    Pachyrhachis, Eupodophis, Haasiophis; Pachyophis… ask Google, and you shall receive.

    Why,if snakes evolved from aquatic ancestors, are there few primitive snakes that are aquatic?

    There are some, they’ve just been dead for a long time.

    how many fossil snakes are less than medium-sized?

    Not all that many; and burrowing animals generally have a bad fossil record.

    Link to this
  31. 31. Tayo Bethel 12:02 pm 01/21/2014

    Correction: In a previous comment I said that snakes seem to have evolvedfrom small fossorial squamates–i should have said medium-sized.

    Are there any known cases in squamate evolution where semi-aquatic forms gave rise to terrestrial ones?

    Link to this
  32. 32. Tayo Bethel 12:10 pm 01/21/2014

    @David:

    Thanks. lol I need to read more thoroughly. :) Oh well–we’ll just have to wait till the least derived fossorial or aquatic snake is found–and even then the topic probably wont be anywhere near closed. Such is the nature of paleontology–many, many questions and always new questions even when we think we know the answers to the old questions. …Actually, that’s science in general :)

    Link to this
  33. 33. Yodelling Cyclist 12:24 pm 01/21/2014

    @David Marjanović: Pachyrhachis, Eupodophis, Haasiophis; Pachyophis… ask Google, and you shall receive.

    Not forgetting my favourite group, palaeophiids. An apparently new post KT bunch Paleocene marine reptiles.

    Link to this
  34. 34. Mark Hutchinson 6:34 am 01/22/2014

    Re snake origins, a few points:
    *The fossil record has candidate fossils for very primitive (with hind limbs) burrowing snakes (Najash, Dinilysia) and sea snakes (listed in previous posts) that are similar in age(Late Cretaceous).
    *So whether snakes evolved in the sea or on land they rapidly occupied the alternative habitat soon after.
    *It is not obvious that land dwelling had to come first, because limbless locomotion can be used in any medium and its evolution in one medium can be seen as an exaptation for invading the others (burrowing, slithering, climbing, swimming). Unlike whales coming back on land, for instance.
    *In the marine origins hypothesis, the snake sister group comprises slender, limb reduced, long-necked, elongate-backboned and not very big (generally less than a metre long) aquatic lizards from the Late Cretaceous (includes dolichosaurs and adriosaurs – Google them).
    *Thus the marine hypothesis, but not the burrowing hypothesis, points to specific fossils that show both close phylogenetic relationships and morphological intermediacy between a limbed lizard and the snake body form.

    And while I’m here, the use of ‘dragons’ in Australia as a common name for agamids I would suggest comes from the fact that Pogona barbata got called the bearded dragon at an early stage, based on its spiny appearance and fierce defensive display. Its fellow agamids therefore had to be some other kind of dragon, didn’t they?

    Link to this
  35. 35. David Marjanović 10:21 am 01/22/2014

    Are there any known cases in squamate evolution where semi-aquatic forms gave rise to terrestrial ones?

    No. Outside squamates, too, this is very uncommon.

    Link to this
  36. 36. canadian 2:28 pm 01/22/2014

    My Uncle Eli got silver Porsche Boxster just by working online… browse around this web-site >>>>>>>>>>>>>>>>>>>>>>>>http://goo.gl/ir34zP

    Link to this
  37. 37. ectodysplasin 7:15 pm 01/22/2014

    @David, the Castoe paper is 2009, not 2008, but is here:

    Castoe, T. A., et al. (2009). Evidence for an ancient adaptive episode of convergent molecular evolution. Proceedings of the National Academy of Sciences, 106(22), 8986-8991.

    Link to this
  38. 38. ectodysplasin 7:23 pm 01/22/2014

    @Mark Hutchinson;

    *Thus the marine hypothesis, but not the burrowing hypothesis, points to specific fossils that show both close phylogenetic relationships and morphological intermediacy between a limbed lizard and the snake body form.

    Both do, really. The burrowing hypothesis emphasizes some morphological character sets, whereas the aquatic hypothesis emphasizes others. It’s also worth pointing out, by the way, that aquatic and burrowing are not mutually exclusive possibilities; there are a number of animals that are both fossorial AND semiaquatic (Lanthanotus is a key example) and that show various snakelike characteristics.

    I don’t think it’s fair to portray this as a settled issue, nor do I think it’s fair to suggest that one group or another has done more to support their arguments on this point. There’s some handwaving on both sides, and there’s also a lot of good fossil material and good ideas on both sides. The problem right now is that there’s still a paucity of fossils and a lot of morphological ambiguity that still remains to be resolved. New material of Najash reported at the 2013 SVP meeting will help resolve this, I think, but there’s still quite a bit more work ahead, both in the field and in the lab, before this thing is settled.

    Link to this
  39. 39. David Marjanović 8:04 pm 01/22/2014

    Thanks for the ref, I’ll check it out tomorrow.

    I’m reading the paper in the November issue of JVP and am liking it a lot so far.

    Link to this
  40. 40. Tayo Bethel 10:08 pm 01/22/2014

    @David:
    Is the JVP paper open access? Link, please.

    Link to this
  41. 41. Mark Hutchinson 3:47 am 01/23/2014

    Ectodysplasin:
    Of course it’s not settled! I pointed out an aspect of the marine hypothesis that I find appealing. Most of what I said was designed to show that marine origins need not rule out terrestrial descendants when the body plan is equally effective in both media. Yes it’s happened before. Tetrapods anyone?

    Link to this
  42. 42. Yodelling Cyclist 8:56 am 01/23/2014

    Settled? Hell, this is palaeontology, where everything’s dead except the comment thread.

    Link to this
  43. 43. David Marjanović 11:09 am 01/23/2014

    Is the JVP paper open access?

    Nope. Find me in http://scholar.google.com/ , drop me an e-mail, and I’ll see what I can do. :-)

    Link to this
  44. 44. ectodysplasin 1:03 pm 01/23/2014

    @Mark,

    Of course it’s not settled! I pointed out an aspect of the marine hypothesis that I find appealing. Most of what I said was designed to show that marine origins need not rule out terrestrial descendants when the body plan is equally effective in both media. Yes it’s happened before. Tetrapods anyone?

    I don’t think the burrowing hypothesis is based in incredulity that a marine organism could recolonize a terrestrial environment. The burrowing hypothesis is more based on the distribution of burrowing morphology in fossil and extant squamates more generally, and in fossil and extant snakes specifically.

    It’s also worth pointing out that there is some manner of disagreement with respect to character formulation between the mosasaur-snake research group and the remainder of the field, so the phylogenies that are generated by one group are not necessarily accepted by others.

    Link to this
  45. 45. naishd 1:29 pm 01/23/2014

    Yup – with respect to that last point (“there is some manner of disagreement with respect to character formulation between the mosasaur-snake research group and the remainder of the field”), Rieppel and Zaher have published whole papers where they go through the characters supposed to support the pythonomorph hypothesis and argue that all (or virtually all) are problematic. Looked at ‘from the outside’, it does seem that the features concerned are the result of convergence and not as similar as initially made out. But, hey, I work with Mike Lee and John Scanlon usually haunts these parts, so we must talk in hushed tones…

    Rieppel, O. & Zaher, H. 2000. The braincases of mosasaurs and Varanus, and the relationships of snakes. Zoological Journal of the Linnean Society 129, 489-514.

    - . & Zaher, H. 2000. The intramandibular joint in squamates, and the phylogenetic relationships of the fossil snake Pachyrhachis problematicus Haas. Fieldiana, Geology, New Series 43, 1-69.

    - . & Zaher, H. 2001. Re-building the bridge between mosasaurs and snakes. Neues Jahrbuch fur Geologie und Paläontologie, Abhandlungen 221, 111-132.

    Zaher, H. & Rieppel, O. 1999. Tooth implantation and replacement in squamates, with special reference to mosasaur lizards and snakes. American Museum Novitates 3271, 1-19.

    Link to this
  46. 46. Biology in Motion 2:23 pm 01/23/2014

    I know this isn’t really part of the core discussion, but regarding mosasaur limbs: the hind limbs are indeed quite robust in overall dimensions for most taxa, but they tend to have relatively weak anchoring (the pelvis is highly reduced and probably did not articulate directly with the vertebral column – see SVP 2012, if memory serves).

    The sternal complex, on the other hand, is enormous and the adductor anchors for the forelimbs are expansive. There are a couple of potential explanations for this offset, but fluid loads during stabilization of rapid swimming is a likely one.

    Alright, back to phylogeny now…

    Link to this
  47. 47. ectodysplasin 5:43 pm 01/23/2014

    @darren,

    Rieppel and Zaher have published whole papers where they go through the characters supposed to support the pythonomorph hypothesis and argue that all (or virtually all) are problematic.

    Well, you’d be hard-pressed to find a morphological phylogeny without at least a few problematic characters. The question more broadly is whether the dataset more generally is robust enough to resist the effects of those characters, or whether the results are largely spurious as a result of those. I think it’s too early to tell which is the case for current snake origin matrices.

    Link to this
  48. 48. Yodelling Cyclist 9:49 am 01/24/2014

    @Biology in Motion: Regarding the mosasaur biomechanics: that’s really fascinating. Why, then, do you suggest that mosasaurs retained hind limbs if they were not well supported? Hydrodynamic lift? Sexual Selection ? Aquatic tetrapods are some of the better examples of convergent evolution (e.g. everyone develops a tail fin of some kind, even mosasaurs) so I’m wondering why the aquatic reptiles kept the hind limbs (icthyosaurs (much reduced hind limbs, iirc), mosasaurs) even when adapting to tunniform niches, whilst mammals (sirenians, cetaceans) have developed “cleaner” lines and lost the hind limbs, even when not active pursuit predators?

    If you get a chance to answer, please use simple terms, remember I’m one of the enthusiasts around here.

    Best wishes
    Yod

    Link to this
  49. 49. Yodelling Cyclist 10:08 am 01/24/2014

    Actually, I think the question should include thalattosuchians as well.

    Link to this
  50. 50. David Marjanović 10:28 am 01/24/2014

    Rieppel and Zaher have published whole papers where they go through the characters supposed to support the pythonomorph hypothesis and argue that all (or virtually all) are problematic

    Also vice versa. The paper I keep talking about and have now read, ref below, shows that Rieppel et al. have assumed that the skulls of all the Cretaceous marine snakes are crushed in quite improbable ways and have also most likely misinterpreted the homologies of skull bones (the jugal in particular) the existence and shape of which are not being questioned. The “prootic flange”, which ought to be pretty far back on the braincase, turns out to be the ectopterygoid process of the pterygoid in the palate, and there goes the evidence for the presence of a “laterosphenoid” in the braincase which would have drawn the Cretaceous marine snakes into a terrestrial clade…

    Alessandro Palci, Michael W. Caldwell & Randall L. Nydam (November 2013): Reevaluation of the anatomy of the Cenomanian (Upper Cretaceous) hind-limbed marine fossil snakes Pachyrhachis, Haasiophis, and Eupodophis. Journal of Vertebrate Paleontology 33(6): 1328–1342.

    Now let’s see if I can write a tree.

    –+–test
    `–test

    –+–test
      `–test

    –+–test
    ..`–test

    Link to this
  51. 51. naishd 10:33 am 01/24/2014

    I haven’t read that paper (not even sure that I’ve seen the Nov’ 2013 issue), but – from memory – the ones on mandibular anatomy and tooth implantation (cited above; comment # 45) seemed pretty compelling.

    Link to this
  52. 52. David Marjanović 11:00 am 01/24/2014

    (icthyosaurs (much reduced hind limbs, iirc)

    Small, but not otherwise reduced, though the pelvis is far from the vertebral column.

    Now for some trees! Palci et al. (2013) made a data matrix and analyzed it three times, with three different outgroups: (1) Heloderma, Lanthanotus, Varanus and Mosasauroidea (no mention of whether that outgroup was set to be mono- or, as the authors clearly believe it is, paraphyletic); (2) Iguana, Agama and Uromastyx; (3) Amphisbaenia, Dibamidae, and the skinks Acontias and Corucia. Using (1) or (2) resulted in the exact same tree, though with different bootstrap values ((2) giving lower ones for stem-snakes and very slightly higher ones for crown-snakes = Serpentes):

    –+–Pachyrhachis
       `–+–Eupodophis
           `–+–Haasiophis
               `–+–Madtsoiidae
                   `–+–Dinilysia
                       `–+–Najash
                           `–Serpentes

    …have to break off here for fear that the column might be too narrow…

    Serpentes
       |–Scolecophidia
       |      |–Leptotyphlopidae
       |      `–+–Typhlopidae
       |          `–Anomalepididae
       `–Alethinophidia
             |–+–+–Anomochilus
             |   |   `–Uropeltidae
             |   `–+–Cylindrophis
             |      `–Anilius
             `–+–+–Xenopeltis
                |   `–Loxocnemus
                `–+–+–Ungaliophiinae
                   |   `–+–Erycinae
                   |      `–+–Pythoninae
                   |         `–Boinae
                   `–+–Tropidophiinae
                      `–+–Bolyeriinae
                         `–+–Acrochordus
                            `–Colubroidea

    In both cases, Ophidia ( = everything shown here) has a bootstrap support of 99 %.

    Everything changes with outgroup (3): Ophidia and Serpentes become synonyms and are contradicted by the bootstrap tree, as is what is now Alethinophidia:

    –+–Scolecophidia as above
       `–Alethinophidia
             |–+–Najash
             |   `–+–Dinilysia
             |      `–+–Madtsoiidae
             |         `–+–Haasiophis
             |            `–+–Eupodophis
             |               `–Pachyrhachis
             `–extant alethinophidians as above

    In other words, all three analyses give the exact same unrooted tree for Ophidia, and then outgroup (3) attaches in another place — next to Scolecophidia — than (1) and (2), which attach next to Pachyrhachis instead.

    From the legend of fig. 8: “Note: [...] the consensus tree from the bootstrap analysis relative to the third data set (tree [...] [with outgroup (3)]) retrieves a monophyletic Ophidia [...], but where the Scolecophidia [...] and the clade formed by all fossil snakes [...] are inverted with respect to their positions in the tree” shown above.

    I find this “clade formed by all fossil snakes” looks highly suspicious. It has very low bootstrap values: the whole thing has 51, the marine clade has 68, and all other values are well below 50.

    I also find the position of Madtsoiidae unexpected and interesting. Aren’t some of these suspected of having been semiaquatic…?

    Link to this
  53. 53. David Marjanović 11:03 am 01/24/2014

    …have to break off here for fear that the column might be too narrow…

    That might have happened if I had used two non-breaking spaces instead of one for every grave accent – as I should have, because now too much doesn’t line up.

    Link to this
  54. 54. David Marjanović 11:07 am 01/24/2014

    Forgot to mention: Palci et al. explicitly exclude Coniophis because they’re thoroughly unconvinced that the unconnected isolated bones referred to it by Longrich et al. (2012) really belong together.

    The data matrix is in the supplementary information; I haven’t looked at it.

    Tooth implantation? I thought it’s quite similar in mosasaurs and snakes?

    Link to this
  55. 55. ectodysplasin 11:54 am 01/24/2014

    @David,

    Forgot to mention: Palci et al. explicitly exclude Coniophis because they’re thoroughly unconvinced that the unconnected isolated bones referred to it by Longrich et al. (2012) really belong together.

    Rightfully so.

    As for tree topologies, the new skulls of Najash should resolve some of the questionable character issues, especially with respect to the postorbital bones.

    Link to this
  56. 56. LeeB 1 5:05 pm 01/24/2014

    Yod,

    mammals lose the hind limbs but they swim by moving the tail flukes vertically; marine reptiles move their tail horizontally and retain the hind limbs.
    Sharks also swim by moving their tail horizontally and they have pelvic fins at about the same position as marine reptiles have their hind limbs.
    So it seems that the hind limbs do not interfere with the hydrodynamics of swimming in animals with a horizontal motion of the tail fin.

    The loss of attachment between the hind limbs and the spinal column via the pelvis is presumably because they no longer have to support their weight when coming ashore to breed, having developed the ability to give birth to live young in water.

    LeeB.

    Link to this
  57. 57. Tayo Bethel 9:30 am 01/25/2014

    @LeeB.

    So what, if anything, werethe hind limbs of mosasaurs being used for?

    @Biology In Motion::

    Are there any papers discussingthe forelimbs, sternal complexes and swimming abilities of mosasaurs?

    Link to this
  58. 58. David Marjanović 10:23 am 01/25/2014

    As for tree topologies, the new skulls of Najash should resolve some of the questionable character issues, especially with respect to the postorbital bones.

    Perhaps not. If it really sits right next to the crown-group, it may well have lost features that Pachyrhachis retains.

    Link to this
  59. 59. LeeB 1 4:21 pm 01/25/2014

    Tayo,

    I don’t know if anyone knows.
    Perhaps if anyone knows if pelvic fins have any effect on the swimming abilities of sharks they could comment.

    As well as the tail fins for locomotion and the pectoral fins for lift and steering and first dorsal fin for stability sharks also have smaller second dorsal, pelvic and anal fins.

    Presumably they have some use as all sharks have retained them; furthermore they differ in size and position in different sharks.

    Even highly streamlined fast swimming Mako sharks retain them; from memory they also have broad horizontal ridges at the base of the tail fin.

    Sorry I can’t help more,

    LeeB.

    Link to this
  60. 60. Yodelling Cyclist 7:35 pm 01/25/2014

    I think LeeB may be on to something. Cheers.

    Link to this
  61. 61. BonesBehaviours 10:47 am 01/27/2014

    The loss of connection between the pelvis and backbone is because it would impede mobility?

    Link to this
  62. 62. David Marjanović 11:25 am 01/27/2014

    Mobility of the backbone, yes.

    Link to this
  63. 63. ectodysplasin 12:46 pm 01/28/2014

    @David,

    Perhaps not. If it really sits right next to the crown-group, it may well have lost features that Pachyrhachis retains.

    From the morphology presented at SVP this year, it’s clear that Najash is pretty far down the snake stem.

    Link to this
  64. 64. David Marjanović 7:21 am 01/29/2014

    I don’t remember that presentation very well, and the abstract doesn’t help. All I can say is that the jugal is also retained in the marine forms.

    Link to this
  65. 65. Biology in Motion 6:58 pm 02/3/2014

    Tayo: I don’t know if there are any papers that summarize the relationships between the pectoral, pelvic, and caudal anatomy in mosasaurs. It seems like there should be, but I have the fortune of being at a museum with a particularly good mosasaur collection, so I just measured them up myself.

    Yodel: I’m sorry I missed your question before. I don’t know if you’ll get a chance to read this, but if so, my best hypothesis for the function of the pelvic fins in mosasaurs would be stabilization and control of the wake as it heads to the tail. In animals that have multiple sets of wings or fins to interact with the fluid they are in (air and water, respectively), the forward set can “prime” the fluid so that the second set gets a more favorable flow to work with. We assign rather verbose names like “wake capture interaction” and “boundary layer control” to those effects, but it basically just means that the animal gets to push on the same bit of water/air more than once.

    Link to this
  66. 66. John Scanlon FCD 12:54 pm 02/9/2014

    I’ve been away a lot; excellent to see that an agamid post evolved into a snake origin discussion.

    Darren, I don’t think it should be assumed that Riversleigh ‘Physignathus‘ fossils are referable to Intellagama at all. The common ancestor of all or most amphibolurines probably had all the features shared by lesueurii and cocincinus, so many of its descendant lineages probably had similar morphology and habits. I’ve mentioned previously (commenting on the GINO post a few years ago) that I’ve prepared additional, older Riversleigh specimens than Covacevich et al. had, and I can’t see that they share any apomorphies with lesueurii.

    Palci et al. (2013) reached the same conclusions on the jugal/ectopterygoid and ‘prootic flange’/pterygoid issues with those Cenomanian snakes as I did in 1996 (regarding Pachyrhachis), 2002 (regarding also Haasiophis) and 2006 (regarding also Eupodophis), based on perusal of published illustrations. It helped me that the 3-dimensionally preserved terrestrial Australian madtsoiids have essentially the same states of those characters as the Cenomanian marine species. This, and much other evidence has been consistently ignored in all analyses supporting fossorial origins…

    Also, my 2005 Wonambi-skull paper dealt with some of the hand-wavey claims in the Rieppel & Zaher braincase one, showing that snake, mosasaur and varanoid braincases are not at all ‘fundamentally different’ as they claimed. Rather, the differences can be described in terms of character states and used in analyses. It’s a radical point of view, I understand.

    Dinilysia and Najash are both about 2 m long, so they can not be considered actual examples of fossorial snakes, although they may well be secondarily surface-active members of a fossorial lineage (or lineages). Reduction of circumorbital bones is very common in burrowing snakes, but I still expect Najash to have jugals forming the postorbital bar, with a big contact on the maxilla. It would be interesting to see if the pterygoid has a big, square ectopterygoid process like madtsoiids, or has reduced it like Dinilysia.

    The clade formed by all fossil snakes makes sense if extinction is a synapomorphy… oh wait. No, it makes as much sense as an outgroup consisting of disparate unrelated highly-derived fossorial squamates, without any of their limbed terrestrial relatives.

    No particular indications of aquatic habits in any Madtsoiidae, but of course they could swim and turn up, like azhdarchids, in some aquatic deposits. Some of the small ones have low neural spines and may have done some burrowing, but nothing is known to test that. The dentition and other evidence implies feeding on lizards and mammals, and of course dinosaurs in Sanajeh.

    Nobody has ever presumed that madtsoiids didn’t have hindlimbs, have they? That would be jumping the gun…

    Link to this
  67. 67. naishd 4:27 pm 02/9/2014

    John – thanks for this comment; I either didn’t know of your opinions on the Riversleigh water dragon material, or had forgotten them, sorry. I will add an edit to the main text. When are you going to publish?

    Snake thoughts appreciated. I really should cover the whole issue here some time. Never have.

    Link to this

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