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Obscure fossil mammals of island South America: Thomashuxleya and the other isotemnids


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Just some of South America's Cenozoic megafauna (more complex versions of this illustration will appear later, and a larger version at different format is shown down below). These animals were not all contemporaneous. L to r: teratornithid, phorusrhacid, thylacosmilid borhyaenoid, toxodontid toxodont, astrapothere (at back), isotemnid toxodont, prothylacinid borhyaenoid, sebecosuchian.

ResearchBlogging.org

I’ve often (or sometimes) said that there are – still, even after more than six years of operation – whole groups of tetrapods where I’ve barely scratched the surface, if that. The recent revisiting of borhyaenoids reminded me how much I love South American Cenozoic megafauna, and how frustrating it is that data on these animals can only be found in the technical literature and is almost never synthesised or made in the least bit popular.

Available on amazon (which is where this cover image comes from).

I should add that this isn’t because the respective specialists and aficionados are uninterested in such an aim – it’s because synthesising the scattered and obscure literature on these animals is difficult, and there’s not all that much incentive to do it (publishers and the public at large display little interest in these animals). The best synthetic treatment remains G. G. Simpson’s 1980 Splendid Isolation, the Curious History of South American Mammals (Simpson 1980), and if you’re seriously interested you absolutely must get hold of this book. Savage & Long’s (1986) Mammal Evolution: An Illustrated Guide isn’t too bad on South American native mammals, and the recent multi-authored volume Bones, Clones & Biomes: The History and Geography of Recent Neotropical Mammals (Patterson & Costa 2012) includes a lot of relevant data and discussion.

As you’ll recall from the borhyaenoid article, island South America was inhabited by diverse metatherian predators. These lived alongside the flightless phorusrhacid birds, an array of xenarthrans (sloths, armadillos, glyptodonts and kin), and an enigmatic set of mostly herbivorous placental mammals – the pyrotheres, astropotheres, xenungulates, didolodontids, litopterns and notoungulates.

What, exactly, is a notoungulate anyway?

Exactly where these placental mammal groups fit within the mammalian family tree remains uncertain, though there are several ideas. In this article I want to start a long-overdue and much anticipated look at notoungulates. There’s so much to say about this group that I can only deal with one small set of species at a time, and here I want to discuss members of just one notoungulate group, Toxodontia. And – because there’s an awful lot to say about toxodonts in general – this article is devoted to one toxodont group alone, Isotemnidae. We’ll get to the others later. How, I hear you ask, are notoungulates identified, and how are toxodonts identified?

Notoungulate upper right molar showing key structures. After diagram in Croft (1999).

The enormous number of taxa grouped together in Notoungulata share an unusual set of cranial, dental and ankle characters, now regarded as synapomorphies that support the recognition of this group as a clade. In the notoungulate skull, the upper molars have what’s called a ‘coronal pattern’: the cusps have been transformed into long crests arranged around the edges of the tooth (the crests are called lophs on the upper teeth, and lophids on the lower ones). A protoloph borders the anterior edge of the tooth, a metaloph along the posterior one, and an ectoloph runs parallel to the tooth’s labial (outer) side. A unique accessory spur – the crochet – projects from the metaloph in the direction of the ectoloph (Simpson 1980, Cifelli 1993, Croft 1999). As usual with tooth cusp characters, this pattern was extensively modified in advanced lineages.

Several key features concern the ear region and the bones surrounding it. The zygomatic arch in the notoungulate skull is attached very high up on the side of the skull [see Toxodon skull shown below], an ‘epitympanic sinus’ is present in the squamosal bone at the back of the skull, a large, bony chamber (an auditory bulla) projects downwards beneath the ear, and the auditory meatus (the bony ear opening itself) is tubular and associated with a bony crest (Cifelli 1993, Gabbert 2004). As usual with weird anatomical characters, this set of features surely means something very interesting but (so far as I know), nobody has ever worked out exactly what that is. Sensitive, low-frequency (infrasonic?) hearing has been suggested (Savage & Long 1986).

Skull of the toxodontid toxodont Toxodon, photographed at Zoologisk Museum, Copenhagen, by FunkMonk. Total length of skull = c. 60 cm. Licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

Within notoungulates, a lengthened molar series, a shelf-like process on the lower premolars (technically, an anterolabial cingulum) and the presence of a lower molar crest called a paralophid unite the toxodonts. Toxodonts are best known for the gigantic (hippo- or rhino-sized) toxodontids of the Miocene, Pliocene, Pleistocene and Holocene. But this is only one of several groups, and in this article we’re going to start going through them. I should note that a number of toxodont taxa – mostly (but not entirely) from the Paleocene and Eocene – have been hypothesised to be ‘basal toxodonts’, outside the clade containing all other species (McKenna & Bell 1997). They include Brandmayria, Colhuelia, Lafkenia, Colhuapia, Allalmeia, Brachystephanus and Xenostephanus.

Introducing the isotemnids

Reconstruction of Thomashuxleya (though see text!), from Simpson (1967).

About 12 toxodont genera from the Paleocene, Eocene and Oligocene are grouped together in Isotemnidae. None can be considered familiar, though a near-complete skeletal reconstruction produced for the Casamayoran* Patagonian form Thomashuxleya externa by Simpson (1967) – shown above – has formed the basis for illustrations in various popular books. It is in fact one of the most familiar toxodont reconstructions in the literature, perhaps being second only to Owen’s depiction of the gigantic toxodontid Toxodon.

* Casamayoran = middle or Late Eocene. One of about 21 terms used in the SALMA (= South American Land Mammal Ages) biochronology.

Thomas H. Huxley photographed c. 1870. From wikipedia, in public domain.

The name Thomashuxleya of course honours Victorian biologist and ‘Darwin’s bulldog’ Thomas H. Huxley. Florentino Ameghino (1854-1911), the great Argentine palaeontologist, naturalist, zoologist and anthropologist who described and named so many South American fossil mammals, was clearly fond of naming taxa after palaeontological colleagues: he also came up with Oldfieldthomasia, Ricardolydekkeria, Guilielmofloweria, Asmithwoodwardia, Carolodarwinia, Ricardowenia and others. Note that all have a latinesque flair.

Simpson depicted Thomashuxleya as being approximately proportioned like a big, robust dog (about 1.3 m in total length) with a relatively large head and obvious upper and lower canines. Vizcaíno et al. (2012) (citing unpublished PhD work by D. A. Croft) provide a mass estimate of 113 kg for Thomashuxleya, with c. 50 kg being given for the other Casamayoran isotemnids Anisotemnus and Pampatemnus.

However, Simpson’s aim to produce an isotemnid reconstruction seems to have been biased by his opinion that all taxa referred to this group were much alike: he considered it acceptable to combine elements from three different taxa in this reconstruction. In fact, it includes elements from Thomashuxleya externa, an unidentified species later referred to Anisotemnus distentus by Shockey & Flynn (2007), and a then-unnamed species that Simpson later named Pleurostylodon simulis.

Incomplete skull of Pleurostylodon modicus, from Simpson (1967).

It turns out that these three are actually quite different, most notably in forelimb proportions and joint morphology. In ulnar shape, Thomashuxleya is more like cursorial carnivorans and ungulates than are either Anisotemnus and Pleurostylodon. In Thomashuxleya, the ulna’s posterior border is concave and the olecranon process (the projecting flange that forms the bony lump of the ‘elbow’) is downcurved. In Anisotemnus and Pleurostylodon, the ulna’s posterior border is convex and the olecranon process curves upwards.

These differences suggest a more erect forelimb posture for Thomashuxleya, and a more flexed – or ‘crouched’ – posture in Anisotemnus and Pleurostylodon. These inferences are further supported by evidence from the distal end of the humerus (Shockey & Flynn 2007). Anisotemnus at least has a hand that appears suited for plantigrady, something you might expect for an animal with a flexed forelimb posture. Thomashuxleya was reconstructed as digitigrade by Simpson (1967) but we don’t know whether this really was the case. Maybe Thomashuxleya had adapted to browsing higher up than those other taxa, or maybe it was more specialised for a fully terrestrial life that didn’t involve any climbing or clambering – I’m speculating, but some aspects of ulnar shape seen in those other isotemnids recall features seen in climbing mammals, so maybe these animals did a bit of climbing and clambering on low branches and such.

Isotemnid ankle bones reveal that the amount of foot and ankle flexibility was quite low – the foot couldn’t be flexed or extended a great deal. An isolated foot (it can’t be referred to any specific isotemnid taxon but perhaps comes from a Pleurostylodon-like form) is pentadactyl with evidence for a divergent hallux. The metatarsals show that the animal – and presumably all isotemnids – had plantigrade hindfeet (Shockey & Flynn 2007). The general conclusion from ankle and foot anatomy here is that these animals couldn’t run and were ‘ambulatory’: walking animals that never really moved that fast, and never used a suspended phase when moving quickly. The caveat here is that both fast movement and running might still have been possible, however, since you can still do those things with inflexible ankles and non-cursorial limbs (Hutchinson et al. 2003).

Speculative life reconstruction of Thomashuxleya externa, by Naish.

In overall proportions, posture and abilities, Thomashuxleya was probably about similar to other robust-limbed mammals of the Paleogene – the pantodonts, astrapotheres and so on. All of these sorts of mammals probably used their robust, sometimes proportionally big, skulls, low-crowned cheek teeth and often big canines to forage among understorey plants for fruits, protein-rich leaves, fungi and so on. There aren’t precise analogues of these sorts of animals in the modern world (forest-dwelling rhinos and hippos come closest), but then, the thickly forested, mostly tropical Paleogene world, with its vast, closed-canopy forests and absence of pursuit predators was quite different from the Neogene one.

Typical isotemnid characters include spatulate incisors and low-crowned cheek teeth, but it has proved hard to find characters that reliably distinguish them from other toxodonts. Simpson (1967) and Cifelli (1993) pointed to the presence of an accessory crest on the lower molars as a possible isotemnid synapomorphy, but even this is known to be variable within the group and it seems to be lacking in some of them, including Thomashuxleya externa (Shockey et al. 2012). It’s also present in other notoungulates (Shockey & Flynn 2007).

Besides Thomashuxleya, Anisotemnus and Pleurostylodon, who are the other isotemnids? Well, there’s Isotemnus, Hedralophus, Pampatemnus, Coelostynodon, Periphragnis, Rhyphodon, Distylophorus, Lophocoelus and Pleurocoelodon (McKenna & Bell 1997). Many of these taxa were named for maxillary or lower jaw fragments, with the key differences being small details of the cusps and associated structures, and the proportions of the teeth relative to one another.

Isotemnids within the toxodont radiation

Isotemnids have generally been considered the sister-group of remaining toxodonts – dubbed the ‘advanced Toxodontia’ by Cifelli (1993) – largely because they lack the derived characters that unite those other lineages (Simpson 1967, Cifelli 1993, Shockey et al. 2012). Furthermore, isotemnids possess a skeletal and dental anatomy that looks suitably ‘ancestral’ compared to what we see in ‘advanced Toxodontia’.

Hypothesised phylogeny of toxodont groups, showing different hand anatomies. Pentadactyl isotemnids are outside the clade in which digits I and V became reduced, and eventually lost. From Shockey et al. (2012).

Isotemnids have broad, pentadactyl hands and feet with blunt hooves, and a ‘primitive’ sort of scapula (where the acromial and metacromial processes overlie the shoulder joint), for example. However, the aberrant, clawed homalodotheriids (or homalodotheres, if you prefer) – we’ll get to them later – were often considered close to isotemnids in the past and indeed Ameghino united both in a group called Entelonychia. You might have guessed that this stems from Ameghino’s idea that these animals were close relatives of chalicotheres. Isotemnids and homalodotheriids were recovered as especially close relatives in some of Cifelli’s (1993) and Shockey et al.’s (2012) trees, and leontiniids (more on them later) group with both of these lineages when postcranial data is excluded from analysis (Shockey et al. 2012). The lesson here is probably that all three groups are conservatively similar in some aspects of morphology, not that they’re necessarily all closer to one another than they are to ‘advanced Toxodontia’.

Simpson (1967) described how isotemnid fossils are among the most commonly found of mammal remains at many sites. They were also among the largest of mammals present in the respective faunas, though it should be noted that Thomashuxleya is much larger than other Casamayoran isotemnid taxa.

And here ends the Tet Zoo guide to isotemnid toxodonts. Isotemnids are nice, but they’re arguably less interesting that the remaining toxodonts. We’ll be looking at those other forms soon enough.

Incidentally, this is Tet Zoo ver 3’s 99th article. What comes next?

For previous Tet Zoo articles on South American Cenozoic megafauna, see…

Refs – -

Cifelli, R. L. 1993. The phylogeny of the native South American ungulates. In Szalay, F. S., Novacek, M. J. & McKenna, M. C. (eds) Mammal Phylogeny: Placentals. Springer-Verlag (New York), pp. 195-216.

Croft, D. A. 1999. Placentals: endemic South American ungulates. In Encyclopedia of Paleontology, Fitzroy Dearborn Publishers (London), pp. 890-906.

Gabbert, S. L. 2004. The basicranial and posterior cranial anatomy of the families of the Toxodontia. Bulletin of the American Museum of Natural History 285, 177-190.

Hutchinson, J. R., Famini, D., Lair, R. & Kram, R. 2003. Are fast-moving elephants really running? Nature 422, 493-494.

McKenna, M. C. & Bell, S. K. 1997. Classification of Mammals: Above the Species Level. Columbia University Press (New York).

Patterson, B. D. & Costa, L. P. 2012. Bones, Clones & Biomes: The History and Geography of Recent Neotropical Mammals. The University of Chicago Press (Chicago and London).

Savage, R. J. G. & Long, M. R. 1986. Mammal Evolution: An Illustrated Guide. Facts on File Publications (New York & Oxford).

Shockey, B. J. & Flynn, J. J. 2007. Morphological diversity in the postcranial skeleton of Casamayoran (?Middle to Late Eocene) Notoungulata and foot posture in notoungulates. American Museum Novitates 3601, 1-26.

Shockey, B. J., Flynn, J. J., Croft, D. A., Gans, P.. Wyss, A. R. (2012). New leontiniid Notoungulata (Mammalia) from Chile and Argentina: comparative anatomy, character analysis, and phylogenetic hypotheses American Museum Novitates, 3737, 1-64 DOI: 10.1206/3737.2

Simpson, G. G. 1967. The beginning of the age of mammals in South America. Part II. Bulletin of the American Museum of Natural History 137, 1-260.

- . 1980. Splendid Isolation, the Curious History of South American Mammals. Yale University Press, New Haven, CT.

Vizcaíno, S. F., Cassini, G. H., Toledo, N. & Bargo, M. S. 2012. On the evolution of large size in mammalian herbivores of Cenozoic faunas of southern South America. In Patterson, B. D. & Costa, L. P. (eds) Bones, Clones & Biomes: The History and Geography of Recent Neotropical Mammals. The University of Chicago Press (Chicago & London), pp. 76-101.

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. Rajita 1:54 pm 07/21/2012

    When I was a kid I had a book, I think illustrated by Zallinger. It had a reconstruction of Thomashuxleya and for some reason the animal fascinated me. But for years I could hardly find anything more of it. So I was happy to see your article. Two years back my friend sent me an article by Agnolin and Chimento titled the Afrotherian affinities for endemic South American “ungulates”. The article was a great interest to me because it suggested that the SA “ungulates” have a link to the Afrotherians, which appear to have developed ungulate like morphologies on multiple occasions. This is also interesting in view of of the convergence of astropotheres and the proboscideans. What is your view on the Afrotherian connection?

    Your reconstructions are very beautiful.

    Link to this
  2. 2. Heteromeles 3:07 pm 07/21/2012

    So not a tapir or peccary type? Hmmm.

    Back when I spent a little time studying Paleocene animals, I was interested to note that the marsupial skulls in Flannery’s Mammals of New Guinea were the best modern analogs I could find for many of the Paleocene mammals, at least in terms of brain size and general lay-out. While I’m not advocating that Papuan marsupials are Paleogene relics or that Toxodons are marsupials, I wonder if there is some useful correlations to be found there. For example, is Thomashuxleya, perhaps, some crude equivalent of a tree kangaroo?

    Link to this
  3. 3. Wilbert Friesen 4:04 pm 07/21/2012

    Highly interesting (an unique !!). I’m looking forward for the next installments.
    But the Isotemnidae are still as enigmatic as ever. 12 Taxa -and except for Pleurostylodon, Anisotemnus and of course the iconic Thimashuxleya- hardly no information.
    When you page through McKenna I see that 8 genera are named by the insanely prolific Ameghino (all between 1897 – 1904) 8 Genera of the 12. It’s a bit too much according to my taste. Two others mysterieus taxa (Periphragnis and Rhyphodon) were named by Roth in 1899.
    Does anybody know whether these taxa have any validity at all (except being named in McKenna) ?

    Link to this
  4. 4. David Marjanović 4:32 pm 07/21/2012

    Just some of South America’s Cenozoic megafauna [...] baurusuchid sebecosuchian.

    Baurusuchids? In the Cenozoic?

    [from Darren: oops, schoolboy error.]

    was clearly fond of naming taxa after palaeontological colleagues:

    Naturally, the favor has been returned: there is a Florentinoameghinia.

    Note that all have a latinesque flair.

    More a Spanish one, actually.

    The authors of Ricardoestesia clearly knew this. *dons welder’s mask*

    the thickly forested, mostly tropical Paleogene world, with its vast, closed-canopy forests

    Yeah, one per continent!

    an article by Agnolin and Chimento titled the Afrotherian affinities for endemic South American “ungulates”

    !!! Ref, please!!!

    Link to this
  5. 5. David Marjanović 4:34 pm 07/21/2012

    Argh. I need to remember that empty lines are automatically doubled by SciAm.

    Link to this
  6. 6. John Harshman 4:47 pm 07/21/2012

    It would be great to have a good, comprehensive treatment not just of the mammals, but of all the South American Cenozoic fauna before the Great Interchange. Splendid Isolation left me with more questions than ever.

    Considering the original Gondwanan fauna, there was clearly a (the) major radiation of suboscines (and perhaps that too was part of your recent South American kick). Other passerines are a much more recent introduction, and as far as I can see all from the north except for Sapayoa. What about the crocodilians? Are the extant ones fairly recent introductions?

    It would be interesting to attempt to attach dates to the entry of all the various taxa into South America, and to count the necessary number of introductions as well. We get monkeys and hystricomorphs in the Oligocene — is that right? Any others at the same time? And if those introductions are clustered, is there a reason?

    Island continents are just fun. And by the way India, during its isolation, is another big gap in the literature as far as I can see.

    Link to this
  7. 7. Heteromeles 7:09 pm 07/21/2012

    Speaking of India, one would naively think that, with the Deccan traps and all, paleontologists would be crawling all over the subcontinent, looking for paleogene samples.

    Link to this
  8. 8. Dallas Krentzel 8:18 pm 07/21/2012

    @ 6. John Harshman

    In reference to the extant crocodilians of South and Central America (which Darren will probably get around to covering soon if he finishes the crocodialian series, which he should! Although I am NOT complaining about a new series on South American mammals), the crocodiles are definitely a recent invasion. Crocodylus itself is only about 12 million years old, and the neotropical clade is estimated to be around 5 million years old. How they got to the New World and what direction they came from is a more contentious issue. In terms of the caimans, however, they’re a much older group. Darren has a link above from TetZoo ver 2 “Purussaurs: monster caimans of the Miocene” that has some relevant info. Crocodiles are much better dispersers in terms of transoceanic crossings than mammals, so they probably don’t tell us much about other groups, although they’re pretty cool on their own.

    @ Darren: I’m very excited about this notoungulate series. It almost excuses you for not going “ballistic” on basal synapsids yet. :)

    Link to this
  9. 9. Rajita 12:46 am 07/22/2012

    >!!! Ref, please!!!
    Afrotherian affinities for endemic South American “ungulates”.
    Federico L. Agnolin, Nicolas R. Chimento
    Mammalian Biology – Zeitschrift fur Saugetierkunde; 36(2):101-108.
    There are others who dispute this relationship.
    The Indian Intertrappean Beds are Late Cretaceous in age. The ones of interest in this context are the Cambay Shale deposits from the Lower Eocene in the Vastan lignite mines. One of the most interesting in this context are the cambaytheriids which some claim to be perissodactyls but they might rather belong to Afrotheria close to the proboscidean clade. This raises the possibility of Afrotherians symmetrically floating over from Africa to both SA and Ind. These deposits also have some interesting primates which might have given rise to the early African primates. Like see here:
    http://manasataramgini.wordpress.com/2009/09/03/primate-evolution-roundup/

    Link to this
  10. 10. David Marjanović 6:19 am 07/22/2012

    Thanks for the ref, I’ll read it tomorrow.

    Caimans and alligators are sister-groups; the caimans seem to have arrived from North America around the beginning of the Paleocene, IIRC.

    Isolation of India: seems to have ended when the Paleocene did, and I’m not aware of any Paleocene continental deposits in India, except for those intertrappean beds that contain the K-Pg boundary and thus contain a few cm of Paleocene. A Paleocene site in India would be massively awesome.

    We get monkeys and hystricomorphs in the Oligocene — is that right? Any others at the same time?

    Yes and no, respectively. And yes, for both monkeys and hystricomorphs, rafting across the South Atlantic is the only explanation that makes sense.

    http://manasataramgini.wordpress.com/2009/09/03/primate-evolution-roundup/

    What – a blog without comments!?! I thought only creationists did that.

    Link to this
  11. 11. naishd 6:21 am 07/22/2012

    Thanks for many comments. Random responses…

    Were isotemnids tapir – or peccary-like (comment 2)? In the most approximate terms – that is, that isotemnids were low-browsing herbivores that ate leaves, fruit and perhaps foraged in leaf litter and soft soil etc. – I suppose they were. But I didn’t want to pursue this sort of analogy because (1) peccaries are cursorial, suited for open habitats as well as densely forested ones, and specialised for biting very hard objects, and (2) tapirs are semi-aquatic/amphibious, have a proboscis, and are more suited for semi-cursoriality and clearings and other open areas than isotemnids would have been.

    Were any of the isotemnids anything like tree kangaroos (comment 2)? I made the comment about climbing and clambering on the basis of a rough similarity between some isotemnid forelimb bones and those of extant climbers (like binturongs). Plus, I was inspired by the fact that pentadactyl Paleogene ‘ungulates’ with semi-divergent thumbs and flexible forelimbs have often been imagined in the past as capable of limited, clumsy climbing – the environment of the time, and the lack of cursorial specialisation in the relevant lineages, probably meant that a bit of adaptation for low-branch climbing/clambering was advantageous. But isotemnids (and the other animals concerned: certain merycoidodontoids, for example) lack features suggestive of anything more than this – no scansoriality or arboreality approaching what’s seen in tree kangaroos. As covered in my tree kangaroo article from October 2011, these animals have a bunch of obvious climbing adaptations.

    Darren

    Link to this
  12. 12. naishd 6:41 am 07/22/2012

    Regarding the affinities within placental mammals of Notoungulates and other endemic South American groups, I’m really interested in the idea that they might be part of Atlantogenata, as indeed has been proposed (I just checked wikipedia’s take on this hypothesis, and [via the Meridungulata article] it links back to Tet Zoo ver 2). If notoungulates (and other S Am endemics) are part of Atlantogenata, the idea that they might be on the afrotherian branch has been seriously considered (in part due to possible links with periptychids, hyopsodontids and phenacodontids) (Asher et al. 2003, Zack et al. 2005, Agnolin & Chimento 2011), and the idea of a position on the xenarthran branch has been mentioned too. Then again, afrotherian links for the S Am endemics have been contested on the basis of tooth eruption patterns (Billet & Martin 2011) and afrotherian-like ankle characters in some S Am endemics were recently argued to be convergent (Gelfo & Lorente 2012). Furthermore, some authors have proposed links with ‘condylarths’ thought to be part of Laurasiatheria (Hunter & Janis 2006) [incidentally, I still mean to find out who or what 'Spiny Norman' is. It's another of those culturally specific references].

    Bottom line – to do this area justice it would need a devoted article.

    Refs – -

    Agnolin, F. L. & Chimento, N. R. 2011. Afrotherian affinities for endemic South American “ungulates”. Mammalian Biology 76, 101–108

    Asher, R. J., Novacek, M. J. & Geisler, J. H. 2003. Relationships of endemic African mammals and their fossil relatives based on morphological and molecular evidence. Journal of Mammalian Evolution 10, 131-194.

    Billet, G. & Martin, T. 2011. No evidence for an afrotherian-like delayed dental eruption in South American notoungulates. Naturwissenschaften 98, 509-517.

    Gelfo, J. N. & Lorente, M. 2012. The alleged astragalar remains of Didolodus Ameghino, 1897 (Mammalia, Panameriungulata) and a critic of isolated bone association models. Bulletin of Geosciences 87, 249-259.

    Hunter, J. P. & Janis, C. M. 2006. Spiny Norman in the Garden of Eden? Dispersal and early biogeography of Placentalia. Journal of Mammalian Evolution 13, 89–123.

    Zack, S. P., Penkrot, T. A., Bloch, J. I. & Rose, K. D. 2005. Affinities of ‘hyopsodontids’ to elephant shrews and a Holarctic origin of Afrotheria. Nature 434, 497-501.

    Link to this
  13. 13. Finback 7:01 am 07/22/2012

    Next up – gorgonopsians!

    Link to this
  14. 14. naishd 7:06 am 07/22/2012

    Incidentally, if anyone wants to see the drawing used at top (the one featuring a collection of Cenozoic South American megafauna) at higher resolution/larger size, I’ve uploaded a larger version here, at my deviantart account.

    Darren

    Link to this
  15. 15. THoltz 9:26 am 07/22/2012

    Darren — shame on you for not knowing your nation’s cultural heritage! Spiny Norman is an enormous hedgehog which plagues the dreams of notorious gangster Dinsdale Piranha in a Monty Python sketch involving organized crime in London. Spiny Norman is assumed to be imaginary, but shows up in the closing credits: http://youtu.be/dLz07TaTDEA

    Link to this
  16. 16. BrianL 9:34 am 07/22/2012

    This promises to be yet another great series!

    Besides suboscines there are of course other avian clades that are likely to have made the crossing from Africa to South America. Arine parrots (given they’re closest to African *Psittacus* and *Poicephalus*), toucans/barbets, trushes, hoatzins…Undoubtedly, there are others.

    As for meridiungulates being afrotheres or sister to them: I’d love it to be true, but at the moment I seriously doubt it. It would actually be second-coolest to meridiungulates as sister to xenarthrans, to me. By the way, how well-supported is monophyly of Meridiungulata anyway? Might we not be looking at multiple independently evolved clades, possibly making all hypotheses true in part?

    Link to this
  17. 17. John Harshman 10:30 am 07/22/2012

    Avian historical biogeography is a tough field. The fossil record helps — if you have one — and so do living species, but not as much as one might hope. There are a great many groups known as fossils from Europe and North America that are now entirely southern in distribution, so present distribution may not be the best guide. It’s also hard to tell just when various continental blocks lost (or gained) connection with each other. We can suppose that South America wasn’t freely connected with Africa after the mid-Cretaceous, say 80ma, and retained some connection to Antarctica until perhaps 35ma. Any divergence of Cretaceous age might be considered part of the original passenger list.

    According to my very quick and very dirty calculations based on the Hackett et al. data, hoatzins diverged from their closest relatives (regardless of what those relatives might be) around that 80ma date, and so could be considered indigenous. There’s no way of knowing if the more recent fossil African hoatzin (if it is a hoatzin) is a migrant from South America or if the extant hoatzin is the migrant.

    From the same source, the divergence between African and South American parrots is mid-Miocene. But which is the migrant? Based on the tree, we might infer that parrots are originally from Australia and/or New Zealand, so entry through Antarctica isn’t out of the question. Is there a parrot fossil record of reasonable age either in Africa or South America?

    I would bet that thrushes came from North America quite recently. And barbets may be old enough to be part of the aboriginal fauna.

    Darren, I too am shocked at your ignorance of Spiny Norman. You have transgressed the unwritten law, and your head may have to be nailed to the floor.

    Link to this
  18. 18. Lars Dietz 10:51 am 07/22/2012

    Wilbert: Simpson revised all mammals then known from the Paleocene and Eocene of South America in his 1948 and 1967 monographs, so I assume that the McKenna & Bell list only includes those that he thought to be valid. I think that’s still the main source for them apart from the original descriptions. Isotemnids are in the second part of the monograph, which can be downloaded for free here.
    BrianL: I think there hasn’t really been any good support for the monophyly of Meridiungulata. The didolodontids and even more basal forms (Kollpaniinae) are clearly related to litopterns and also seem to be related to North American mioclaenids (de Muizon & Cifelli 2000). Notoungulates have also been suggested to be related to that group, but that’s not quite clear. Pyrotheres seem to be specialized notoungulates (Billet 2010), so that would unite all “meridiungulates” except for xenungulates and astrapotheres, which may be related to each other.
    Billet, G. (2010): New Observations on the Skull of Pyrotherium (Pyrotheria, Mammalia) and New Phylogenetic Hypotheses on South American Ungulates. Journal of Mammalian Evolution 17(1): 21-59.
    Muizon C. de & Cifelli R.L. (2000): The “condylarths” (archaic Ungulata,Mammalia) from the early Palaeocene of Tiupampa (Bolivia): implications on the origin of the South American ungulates. Geodiversitas 22 (1) : 47-150.

    Link to this
  19. 19. naishd 12:57 pm 07/22/2012

    Spiny Norman: how embarrassing. Until now I’d assumed it was a kid’s character, something like Curious George (unknown outside of North America, until his guest appearance in Forrest Gump and the animated cartoon series). I shall diminish, and go into the west.

    Darren

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  20. 20. Therizinosaurus 6:51 pm 07/22/2012

    I too look forward to this series. It seems that it’s not just the popular literature which is lacking for notungulates, but the technical literature as well. When’s the last time you had to refer to a paper from the 60s often when discussing a theropod family?

    Regarding notungulates’ placement in mammal phylogeny, the only good analysis that I know of is Zack’s (2009) thesis, which found them to be closest to perissodactyls among living orders when the topology was constrained to match molecular results.

    Link to this
  21. 21. BilBy 7:58 pm 07/22/2012

    @naishd – re: Spiny Norman – there seems to be an expectation among non-Brits than anyone originally from these islands should know everything about Monty Python, imbibed with mother’s milk as it were, and that in any bar in any corner of the world immediate friendly conversation can be struck up by saying “British eh? This is an ex-parrot!…” etc. It can be dangerous to admit to being too young for the series and that you don’t find what you have seen than funny anyway. Be warned and learn all the lyrics to the lumberjack song.

    Link to this
  22. 22. John Harshman 9:44 pm 07/22/2012

    Wait…there are people who don’t know all the lyrics to the lumberjack song?

    Link to this
  23. 23. Dartian 6:35 am 07/23/2012

    Great article, Darren!

    Toxodonts are best known for the gigantic (hippo- or rhino-sized) toxodontids of the Miocene, Pliocene, Pleistocene and Holocene.

    The Holocene? Whut?

    John:
    We get monkeys and hystricomorphs in the Oligocene — is that right?

    Actually, it has recently been shown that caviomorph rodents were already present in South America in the Eocene (Antoine et al., 2012).

    Darren:
    Curious George (unknown outside of North America, until his guest appearance in Forrest Gump and the animated cartoon series)

    Not true; the Curious George books have been translated to several languages, decades ago.

    Reference:
    Antoine, P.-O., Marivaux, L., Croft, D.A., Billet, G., Ganerød, M., Jaramillo, C., Martin, T., Orliac, M.J., Tejada, J., Altamirano, A.J., Duranthon, F., Fanjat, G., Rousse, S. & Salas Gismondi, R. 2012. Middle Eocene rodents from Peruvian Amazonia reveal the pattern and timing of caviomorph origins and biogeography. Proceedings of the Royal Society B 279, 1319-1326.

    Link to this
  24. 24. naishd 6:42 am 07/23/2012

    Dartian, thanks for compliment. Toxodontids in the Holocene: so far as I know, it is generally accepted that Toxodon persisted into the early Holocene. Baffa et al. (2000) dated a Toxodon tooth to 6700 yrs ago.

    Baffa, O., Brunetti, A., Karmann, I. & Dias Neto, C. M. 2000. ESR dating of a Toxodon tooth from a Brazilian karstic cave. Applied Radiation and Isotopes 52, 1345-1349.

    Curious George: when I said “unknown outside of North America”, I evidently meant “unknown to me”. I admit, I am naive when it comes to Curious George (what an odd phrase).

    Darren

    Link to this
  25. 25. naishd 6:50 am 07/23/2012

    Oh – and, Monty Python. There’s some aspects of Monty Python nerdage that I really dislike – in particular, the fact that a huge number of people seem unable to think of parrots without quoting, or referring to, the sketch about the Norwegian Blue. It’s even made appearances at conferences and such.

    Darren

    Link to this
  26. 26. Tayo Bethel 6:51 am 07/23/2012

    LOL Which lumberjack song?

    Any chance of an article on neosuchians?

    Link to this
  27. 27. Dartian 7:01 am 07/23/2012

    it is generally accepted that Toxodon persisted into the early Holocene

    Wow, I didn’t know that!

    But then again, I didn’t know that ‘nerdage’ is a word either… ;)

    Link to this
  28. 28. naishd 7:09 am 07/23/2012

    Tayo: more crocodyliforms in time (neosuchians in particular, actually), be patient.. (smiley).

    Darren

    Link to this
  29. 29. BilBy 7:38 am 07/23/2012

    Darren – MP nerdage – exactly; and all one can do is give a pained smile in case you are accused of comedy treason – sigh -. Anyway, more to the point, will you be doing anything on litopterns?

    Link to this
  30. 30. naishd 7:47 am 07/23/2012

    Yes, I’ve been collecting stuff on litopterns for years – not easy, much of it is hard to get. Must get through toxodonts, crocodiles, petrels and other stuff first though…

    Darren

    Link to this
  31. 31. Wilbert Friesen 8:11 am 07/23/2012

    18. Slainte Lars,

    Thank you very much, it’s much appreciated.

    Link to this
  32. 32. Heteromeles 10:43 am 07/23/2012

    re: Monty Python. You mean to tell me that, in the UK, the audience doesn’t spontaneously break into “Always look on the bright side of life” during difficult thesis defenses? I’m so disappointed.

    Link to this
  33. 33. Wilbert Friesen 11:00 am 07/23/2012

    Nudge, nudge
    Wink, wink
    Could be taken on a holiday
    Say no more…

    Link to this
  34. 34. David Marjanović 2:00 pm 07/23/2012

    By the way, how well-supported is monophyly of Meridiungulata anyway?

    There is no phylogenetic analysis other than the unpublished one by Zack (2009); is it available somewhere online?

    According to my very quick and very dirty calculations based on the Hackett et al. data

    How did you calibrate it?

    Based on the tree, we might infer that parrots are originally from Australia and/or New Zealand

    (That’s crown-parrots, of course.)

    Link to this
  35. 35. John Harshman 6:25 pm 07/23/2012

    How did you calibrate it?

    Solely based on Vegavis calibrating the anatid node on a tree made ultrametric by non-parametric rate smoothing. Like I said, quick and dirty.

    Are there any stem-parrots? And are they so on the basis of a phylogenetic analysis including the NZ parrots? I presume we’re not counting the Cretaceous “parrot mandible”. Something in the Messel, perhaps?

    Link to this
  36. 36. Heteromeles 6:41 pm 07/23/2012

    @John: Is Mopsitta tanta still considered a parrot? It’s 55 myo and from Scandanavia. No idea if it was blue or not.

    Link to this
  37. 37. naishd 7:02 pm 07/23/2012

    Here’s the section on parrot history and stem-parrots from Naish (2012)…

    Phylogenies indicate that the parrots of New Zealand (such as the kea Nestor notabilis and flightless kakapo Strigops habroptilus) and the Australasian cockatoos are the most basal extant taxa (Wright et al. 2008); this has supported the conclusion that crown parrots originated in Gondwana, perhaps before its fragmentation. However, dispersal across oceanic barriers was apparently important in the history of the group, with independent dispersal events explaining the affinities discovered between widely dispersed parrot taxa (Schweizer et al. 2010). Furthermore, the diversity of parrots in Miocene Europe (all of which are probably close to, but not part of, the crown group) implies Northern Hemisphere origin and diversification, with subsequent dispersal to the southern continents.
    Several zygodactyl Eocene birds from Europe and North America seem to be stem psittaciforms. They have most often been termed pseudasturids, but because Halcyornis from the London Clay of the Isle of Sheppey (the earliest named fossil bird) is referable to this group, their correct name is Halcyornithidae. Unlike crown parrots, halcyornithids have elongate, slender humeri and superficially mousebirdlike skulls. The Eocene messelasturids also now seem to be stem psittaciforms and the sister group to Halcyornithidae (Mayr 2011b). Messelasturids combine a deep, hooked bill with large supraorbital processes and semizygodactyl feet with (in Messelastur) raptorlike unguals. These features led to previous proposals that messelasturids are close relatives of owls and/or diurnal raptors. Their raptorial features suggest carnivorous habits. Additional stem parrots–Vastanavis, Quercypsitta, and Psittacopes–are known from the Eocene of Europe and India. Stem parrots were evidently abundant and diverse in the Northern Hemisphere during the Eocene.

    Darren

    Link to this
  38. 38. THoltz 7:53 pm 07/23/2012

    I was under an impression that you were a nominally Python-worshipping nation: http://youtu.be/asUyK6JWt9U

    :-)

    Python-stuff aside: this is very cool information about the South American placentals!

    Link to this
  39. 39. John Harshman 8:31 pm 07/23/2012

    It seems to me that Miocene crown parrots are too recent to be relevant to the origin of the order, and that stem parrots are not very relevant, at least if they’re widely distributed. For the record, my wild estimate (same source at the others) puts the divergence between cockatoos and other parrots (excepting the NZ ones, which unfortunately weren’t in the published data set) at 26ma. The shortage of Gondwanan material, and especially of Antarctican material, makes life very difficult for historical biogeography.

    Mopsitta? Well, Mayr & Bertelli don’t think it shows any psittaciform synapomorphies at all.

    Link to this
  40. 40. farandfew 1:08 am 07/24/2012

    I have this general impression that mammalian herbivores in the later Cenozoic can be mostly grouped into either 1) cursorial, 2) arboreal, 3) able to defend themselves by sheer mass & strength, 4) able to defend themselves by being small and hide-able. Clearly there are some exceptions like, say, capybara but I have the impression that there used to be more exceptions, at least in the Paleogene, like these isotemnids for instance.
    Is this valid, or is it just that less familiar animals get reconstructed as more generalist due to unwarranted assumptions, or simple parsimony, or both?
    The idea of a medium-sized plantigrade herbivore seems kind of odd.

    Link to this
  41. 41. Dartian 2:57 am 07/24/2012

    farandfew:
    there are some exceptions like, say, capybara

    ‘Cursoriality’ is one of those surprisingly-hard-to-define concepts; however, by most definitions, the capybara would qualify as a cursorial mammal (Stein & Casinos, 1997).

    The idea of a medium-sized plantigrade herbivore seems kind of odd.

    Wombats.

    Reference:
    Stein, B.R. & Casinos, A. 1997. What is a cursorial mammal? Journal of Zoology, London 242, 185-192.

    Link to this
  42. 42. David Marjanović 4:35 am 07/24/2012

    Solely based on Vegavis calibrating the anatid node on a tree made ultrametric by non-parametric rate smoothing. Like I said, quick and dirty.

    That’s a calibration with a high geologic age that lies outside the clade of interest. Both of these facts cause divergence dates to be overestimated (Brochu 2004a, b, 2006; myself & Laurin 2007: especially appendix 10).

    diversity of parrots in Miocene Europe

    :-o I had no idea! I only knew about the Eocene ones!

    The Eocene messelasturids also now seem to be stem psittaciforms and the sister group to Halcyornithidae (Mayr 2011b).

    :-o

    and that stem parrots are not very relevant, at least if they’re widely distributed

    None has yet been found in Gondwana. (India already touched Asia at the time of Vastanavis.)

    psittaciform synapomorphies

    Autapomorphies. One taxon has autapomorphies (auto- = self), two sister-groups have synapomorphies (syn- = together) that are the autapomorphies of the smallest clade they both belong to. Hennig liked inventing terminology just for the fun of it, and he knew his Greek. (“Sister-group” was _adelphotaxon_ to him.)

    Link to this
  43. 43. BrianL 4:46 am 07/24/2012

    @Darren
    Why do you think those Miocene European parrots (*Archaeopsittacus*, *Xenopsitta*, *Bavaripsitta*…)are outside the crown-group? Have they been tested in this regard or is it an assumption of your own?

    To be honest, I see very little reason to assume a northern origin for crown-group parrots of any kind, since all extant lineages (and face it, we really don’t have much else to go on unless your Miocene parrots have truly been cladistically tested) are very much southern. Given the very poor avian fossil record of the Paleogene southern hemisphere, the abundance of stem-parrots in Europe is not neccessarily evidence for a northern origin of stem-parrots and much less for crown group-parrots. It would also seem odd that the basal nodes among the latter originated in New Zealand and Australia if crown group-parrots indeed originated in the northern hemisphere!

    To me, a Sahul/Antarctica origin seems much more likely, with multiple invasions of New Zealand, Africa and the Indian Ocean islands from there. American parrots would then, in turn, be descended from a single invasion of South America from Africa. Given how crownward American parrots are and that they, as a clade, don’t seem to be all that ancient, that seems more likely to me than that they directly spread from Australia. Speaking of them, there’s also fossil *Conuropsis fratercula* from the Miocene of Nebraska. I consider its identification as a parrot rather dubious, much less its assignment to recently extant *Conuropsis*. If it is indeed an arine parrot, it might indicate a northern origin for the clade or an early invasion of the northern hemisphere. If the first, that would be the only evidence for crown group parrots spreading south from the northern continents that I can think of.

    @John Harshman:
    A 26 mya divergence between cockatoos and ‘parrots proper’ seems extremely recent to me. While I certainly don’t buy a Cretaceous origin for psittaciforms, an late Eocene or Oligocene divergence of cockatoos seems reasonable to me. Why do you think it should be placed at 26mya?

    Link to this
  44. 44. Lars Dietz 5:57 am 07/24/2012

    On the phylogenetic status of Miocene European parrots, remember that they’re known only from isolated bones, mostly tarsometatarsi. Mayr’s description of Bavaripsitta ballmanni (online here) concludes that none of them can be confidently placed within any modern parrot group, which of course doesn’t mean that they’re necessarily outside the crown group either.

    Link to this
  45. 45. farandfew 5:58 am 07/24/2012

    Dartian:
    wombats
    Well, yeah, wombats seem kind of odd, I just can’t shake the feeling that they ought to be a lot bigger.
    Something more or less dog or civet shaped and plantigrade and herbivorous seems even weirder.
    I was definitely using ‘cursorial’ sloppily to refer to animals which seemed to both move fast and to have limbs which were, in some way or another, attenuated. I wasn’t thinking about parasaggital gait and was even semi-consciously including the majority of macropods. But yes, I suppose capybara are cursorial. So yes, what isn’t – apart from wombats, that is? And pandas.

    Link to this
  46. 46. BrianL 6:29 am 07/24/2012

    @farandfew:
    Do Old World porcupines qualify or are they ‘cursorial’ like capybara? What about binturongs? They’re largely arboreal, though. How about some of the larger extinct lemurs? Cave bears? *Tremarctos*, even?

    Link to this
  47. 47. Lars Dietz 7:14 am 07/24/2012

    Do gorillas count as non-cursorial ground dwelling herbivores? I can’t see why not.

    Link to this
  48. 48. Andrew O 8:24 am 07/24/2012

    Some of the Papionins are mostly terrestrial, and there’s always castor.

    Among recently-extinct taxa, there’s Nuralagus, the paranthropedes/robust australopithecines, and Megalocnus and other sloths that didn’t take the route of either extreme gigantism or arboreality.

    (There’re also several midsized, ambulatory, non-arborial myrmecophagous species: Myrmecophaga, Priodontes, probably the bibymalagasy, and debatably the aardvark and some of the larger pangolins.)

    Link to this
  49. 49. David Marjanović 9:28 am 07/24/2012

    Given how crownward American parrots are

    Uh, extant ones?

    The crown-group of a taxon consists of the last common ancestor of all extant members of the taxon, plus all descendants of that ancestor.

    By definition, all extant parrots are crown-group parrots. They’re all equally… infinitely crownward. :-)

    paranthropedes

    :-) Hypercorrectivism. There is no pous in anthropos.

    Link to this
  50. 50. Heteromeles 10:28 am 07/24/2012

    Mid-sized plantigrade herbivores. How about pandas?

    I like to look for modern analogies, and to me, the Paleocene seems to be most like Papua New Guinea. Not a lot of large land predators (aside from non-venomous snakes and some birds), and lots of forest. The other thing is that, in a weird way, the Paleocene was sort of a world-wide island. Lots of clades were in a mode of adaptive radiation and experimentation, and the great arms races (carnivores vs. herbivores) hadn’t really got going yet. Of course, most of that adaptive radiation got pruned away by the PETM and so forth, but reading about it is sort of like reading about the dot.com boom in the 90s, in that many species’ business plans don’t make much sense today, unless the animal is living on an island habitat with few competitors or predators.

    Link to this
  51. 51. llewelly 11:29 am 07/24/2012

    45. farandfew 5:58 am 07/24/2012 :

    Dartian:
    wombats
    Well, yeah, wombats seem kind of odd, I just can’t shake the feeling that they ought to be a lot bigger.

    Darren briefly mentions giant wombats here:

    http://blogs.scientificamerican.com/tetrapod-zoology/2011/10/29/vombatiforms-part-ii/

    “Both Phascolonus (with spatulate incisors) and Ramsayia (with narrow incisors) stood about 70 cm tall at the shoulder; the former has an estimated mass of 250 kg. “

    Link to this
  52. 52. BrianL 12:01 pm 07/24/2012

    @David Marjanovic:
    Of course all extant parrots are the crown clade, my bad. What I meant to say was ‘derived’. In the sense that arines are presumably among the last major clades of modern parrots to diverge. Even then, I think we ought to consider that divergence to have taken place in the Oligocene or early Miocene at the latest. Given that neither arines nor psittacines (*Psittacus* + *Poicephalus*, sister to arines) have a fossil record before the Plio-Pleistocene, as far as I know, there is preciously little to base that on, though. I mentioned *Conuropsis fratercula* but I don’t know how well-supported the identity of this putative Miocene arine is. I doubt it was placed in an ‘extant’ genus for any reason other than biogeography.
    Speaking of which, and now I’m going to rant, I have serious reservations about fossil birds from the Oligocene or all but the latest Miocene being placed in extant genera. Not just because of the often fragmentary material and the limited avian fossil record making it difficult to assess what are plesiomorphic characters, but also because of phylogenetic nomenclature. Are we seriously to assume that Oligocene *Pelecanus*, for instance, is descended from the most recent concestor of the extant members of the genus? When dealing with Oligocene avian taxa, I think we can be highly sceptical of that. If a taxon is not descended from that most recent concestor of its closest living relatives, I think it ought to be placed in a different genus for that reason.
    Monotypic genera like *Conuropsis* might be more problematic in that case, as a clade can be newly defined to include both the extant and extinct species, I supppose. Even then, I suspect insisting on the validity of placing *Conuropsis fratercula* in that genus would at the very least neccessate sinking several, many or even all extant arine genera into *Conuropsis*…which would then presumably become *Ara* for reasons of priority.

    Link to this
  53. 53. John Harshman 12:38 pm 07/24/2012

    A 26 mya divergence between cockatoos and ‘parrots proper’ seems extremely recent to me. While I certainly don’t buy a Cretaceous origin for psittaciforms, an late Eocene or Oligocene divergence of cockatoos seems reasonable to me. Why do you think it should be placed at 26mya?
    Like I told David M., it’s all based on a simple rate-smoothing of the Hackett et al. tree, calibrated using Vegavis. You may not like it, and I certainly don’t think we can place much confidence in it, but what else do you have to go on? Why does anything in particular “seem reasonable” to you? And hey, 26ma is Oligocene.

    Anyone is free to do the same exercise. Or if anyone wants to send me a different calibration point, I’ll tell you what constant to multiply my dates by. I would in fact prefer an analysis, using a different algorithm, that makes use of multiple, local calibration points, but that has proven computationally unfeasible so far.

    OK, a 26ma divergence (if you believe it) means we can pretty well rule out vicariance based on plate tectonics as a cause of the basal splits in parrots, and also any completely overland dispersal through Antarctica. It still remains possible that African parrots came from South America rather than vice versa. There is no phylogenetic or fossil reason to prefer one hypothesis over another. There may be other reasons, though.

    As for “synapomorphy” vs. “autapomorphy”, it all depends on whether you’re thinking about the multiple members of a taxon or the single taxon itself. Psittaciformes is singular, and has autapomorphies. Psittaciforms are plural, and have synapomorphies.

    Of course all extant parrots are the crown clade, my bad. What I meant to say was ‘derived’. In the sense that arines are presumably among the last major clades of modern parrots to diverge.

    Urk. Don’t dig this any deeper. Extant taxa are all equally “derived”, which is at any rate a term you should apply to character states rather than whole taxa. Last major clades to diverge? From what, the main line of parrot evolution? This all requires you to objectively define what a “major clade” is, which isn’t really possible. It’s a terminological mess.

    Link to this
  54. 54. John Harshman 12:52 pm 07/24/2012

    Curse you, HTML codes.

    [from Darren: I had a go at cleaning up. Should look better now.]

    Link to this
  55. 55. BrianL 12:57 pm 07/24/2012

    @John Harshman
    Thanks for your clarification and apologies for the 26mya. For some reason I was thinking this was somewhere in the Miocene. We’re in agreement after all, then.

    Of course, ‘major clade’ is subjective. Using the modern ideas of parrot phylogeny, the tree would be like this: (Nestoridae + Strigopidae(Cacatuidae( Psittacinae + Arinae( Psittaculidae). I made this as simplified as possible, while naming Arinae explicitly instead of lumping it with Psittacinae as Psittacidae. In that sense, Arinae is ‘a major clade’ in that it’s one of the main constituents needed to meaningfully illustrate basic parrot phylogeny. This tree suggests that arines diverged rather late, among extant parrots and *could* (emphasis emphasis emphasis) be considered ‘derived’.

    Am I mistaken here or is it simply impossible to word this any way that might not imply anything that just might be remotely objectionable to some of us? Accuracy is one aim, but I wonder if clarity might not be sacrificed when one has to dance on tiptoe around certain terms that are actually useful to describe what you mean. But let’s not turn this into one of THOSE discussions.

    Link to this
  56. 56. John Harshman 9:57 pm 07/24/2012

    BrianL:

    Yes, I think you’re mistaken. You are arbitrarily singling out one node as a “major clade” and then arbitrary building other “major clades” around it. Why is this “Psittaculidae” just one “major clade” instead of, say, four or five? Why don’t fig parrots, for example, deserve their own “major clade”? It’s all arbitrary. And even if you can objectively say that clade X is older than clade Y, what does that have to do with being derived? I don’t think the terms you want to use are useful, precisely because they create false impressions. (And when considering the ages of clades, you should differentiate between node-based ages and branch-based ages.)

    Link to this
  57. 57. naishd 5:16 am 07/25/2012

    I was going to elaborate on parrots (in particular on the Miocene forms and on where they might go in the phylogeny). But given the substantial interest shown here in the comments, it’s clear we need an article devoted to them entirely. I’ll get to it when time allows.

    Darren

    Link to this
  58. 58. David Marjanović 9:23 am 07/25/2012

    Papua New Guinea. Not a lot of large land predators (aside from non-venomous snakes and some birds)

    And that giant monitor… and the dog, formerly the thylacine. But still. Oh, I guess there must have been Quinkana.

    The other thing is that, in a weird way, the Paleocene was sort of a world-wide island. Lots of clades were in a mode of adaptive radiation and experimentation, and the great arms races (carnivores vs. herbivores) hadn’t really got going yet. Of course, most of that adaptive radiation got pruned away by the PETM and so forth, but reading about it is sort of like reading about the dot.com boom in the 90s, in that many species’ business plans don’t make much sense today, unless the animal is living on an island habitat with few competitors or predators.

    Good point!

    This has been offered as an explanation of why almost all paleognaths became flightless.

    Link to this
  59. 59. John Scanlon FCD 11:24 am 07/25/2012

    Maybe it’s just me, but Darren’s drawing of Thomashuxleya made me think of a hundred-kilo Bilby. It was probably the bicoloured tail that started this thought, but it sure would be interesting to see what bandicoots could have done if they’d evolved larger body size.
    John H, I don’t suppose the Riversleigh cacatuid helps much with parrot calibration?

    Link to this
  60. 60. John Harshman 3:24 pm 07/25/2012

    Riversleigh cacatuid: Not really. It merely constrains a node, apparently the one uniting cockatoos with most parrots, to be older than 16ma. Which it already is in my primitive analysis. It would be a useful data point if that analysis allowed for more than one calibration point, which it doesn’t. You can always set the calibration using that fossil, which would make all nodes only 16/26 of the ages I give. But that would have the effect of making Vegavis only 42ma.

    Link to this

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