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Cretaceous “ungulates”

February 16, 2013
Protungulatum jaw.

Protungulatum jaw.

By now, anyone who thinks mammals were small, shrew like critters in the Mesozoic is deluded. While definitely far less anatomically varied than nowadays, mammals spawned several lineages, from aquatic critters to wolverine sized predators. Some even competed with dinosaurs in several ecological niches, and one of said niches was of small herbivores.

In recent years, several genera that appear to have been ungulate-like have been recovered from the Maastrichtian, and some date as early as the Campanian. The most iconic are the indian Kharmerungulatum and the north american Protungulatum, the latter hailing from Hell Creek and likely having co-existed with Tyrannosaurus rex. These mammals have large, rectangular molars with extensive grooves and jagged cusps that imply an almost certainly herbivorous/omnivorous diet, something that only one other group of Mesozoic mammals, the multituberculates, were previously known to have. Most importantly, they are very similar to the teeth of other ungulates, such as the numerous Palaeocenic “condylarth” clades, which they may or may not be related to.

Where in the tree of life do these mammals fit?

Normally described as “condylarths”, that it an almost misleading classification, as Condylartha is now considered polyphyletic, and most of the caldes within it are now thought to not be especially closely related to each other. However, it’s interesting that Cretaceous ungulates might in fact be closely related, or even ancestral, to major Cenozoic ungulate clades.

Protungulatum is classified as a sister genus to Cetartiodactyla in J. R. Wible, G. W. Rougier, M. J. Novacek and R. J. Asher’s 2007 description. If so, this would mean that Laurasitheria was both existent in the KT event and that was already very diverse, with all modern branches already set. That the earliest Protungulatum fossils date to the Campanian extend this laurasitherian radiation probably as back in time as 80 million years. On the other hand, J. David Archibald, Yue Zhang, Tony Harper and Richard L. Cifelli’s 2011 description renders this dubious at best, and indeed according to them it is probably a non-placental eutherian.

Kharmerungulatum is even less clear, but there have been some suggestions that it is a basal meridiungulate, a logical conclusion based on it’s gondwannan location. It may also be the sister taxa to the mysterious Palaeogene Tingamarra, implying that a radiation of basal meridiungulates or at least basal ungulate-like mammals once occured in eastern Gondwanna.

Implications

With the appearence of these mammals, it seems clear that competition with dinosaurs was even less of an issue than previously thought, and given the relative rarity of small ornithopods, it might imply that these mammals arose to fill an ecological void (I should mention that new non-hadrosauroid ornithopods have shown up in the late Cretaceous fossil reccord, though on average they seem to be medium sized animals). Most importantly, it also might mean that modern placental clades were already beginning to get established, or that ungulate-like forms predate the appearence of true placentals.

 

That Protungulatum survived the KT event seems also to suggest that the previous size limits for it’s survivors are likely incorrect.

14 Comments leave one →
  1. cynodont permalink
    February 20, 2013 10:49 pm

    Not surprising. Ungulate morphology converged at least twice among placentals and once among marsupials.

    • February 20, 2013 11:13 pm

      Technically at least five times within placentals, what with the paenungulates and with the highly polyphyletic “Condylartha”.

  2. cynodont permalink
    February 21, 2013 1:52 am

    Honestly, I only kmow of “Ungulata” in laurasiotheres and the elephant-hyrax-aardvark-sirenian+arsinotheres+desmostylian clade in Afrotheria. I really hope a comprehensive phylogeny of Eutheria comes out SOON! It would be awesome if Pegasoferae turns out to be true and mesonychids nest within artiodactylidae and hyeanodonts are afrothere and oxyeanids are actually stem eutherians or…..metatheres.

  3. March 1, 2013 5:47 pm

    These super-fragmentary creatures always drive most people to nuts in most “No K-T” scenario alternative projects, I assure you that…

    Also, some new guy from the AltEvo section has encouraged you to see someone else’s project which is in this link: http://s1.zetaboards.com/Conceptual_Evolution/topic/5046793/… It’s worth a looksee in my opinion

    • March 1, 2013 5:48 pm

      Cannot see it; I was blocked off, remember?

      • Hayaba permalink
        March 2, 2013 7:19 am

        In Terra,Dino-Ken says Afrotheres are non-existant but has Hyeanodonts be th Ancestors of his world’s Canids.

      • March 2, 2013 1:23 pm

        That’s just bizarre. Does he mean canine-analogues or actual canines? If the latter, no, just no.

        (Also, hyeanodonts are macroscelidean afrotheres. Just direct him to the Spec yahoo group and Tetrapod Zoology comment sections)

  4. Hayaba permalink
    March 2, 2013 11:06 pm

    He means Canine Analouges and he says that Mustelid and Ursid Analouges are derived oxyeanids.And also,he has dinosaurs still dominant despite 1/3rd of dinosaur lines dying out in his alternate K-Pg.

    • March 2, 2013 11:40 pm

      Sounds more reasonable.

      • Hayaba permalink
        March 3, 2013 2:22 am

        And View on Afrotheres being non-existant in Terra according to Dino-Ken?And also,view on Land-Crocs being too few in Terra as well?

      • March 3, 2013 10:06 am

        Quite bizarre and non-sensical.

      • Hayaba permalink
        March 3, 2013 11:21 am

        How so,JohnFaa?And Dino-Ken’s Tyrannosaurs are actually Descendants of Dryptosaurids,Alioramus,and Nanotyrannus

      • March 3, 2013 12:44 pm

        Because terrestrial crocodyllians were an large component of Late Cretaceous terrestrial faunas and reltively generalistic when compared to dinosaurs.

  5. Hayaba permalink
    March 8, 2013 12:42 pm

    JohnFaa,in Terra Condyarchs are the Anteater,Chalicotheres,and Ground Sloths of the eorld.

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