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Visual references for Dryolestoidea

December 22, 2016

Researching extinct mammals can be extremely taxing, especially when most you have are teeth and jaws and when what aren’t teeth and jaws is often only ever available in pay-walled, often esoteric texts.

Ditto for dryolestoids, one of the most fascinating of non-therian mammal groups; you wouldn’t guess that a clade spanning at least 60 species across all continents from the Jurassic to the Miocene, ranging from insectivores to hyrax-like herbivores to diggers to weird tusked pseudo-pigs, would have little more than a few pics that aren’t teeth in its name. And sometimes even those are hard to get by!

So here’s some aid:

A possible template?

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So before we get to the many fossil dryolestoids, we should get to what might be a living representative of this clade(!). According to one 2014, the living “marsupial” moles might actually be dryolestoids rather than marsupials.

Thus, it’s a tempting idea to keep Notoryctes in mind. Even if it is a marsupial after all, it is nonetheless very similar to at least one dryolestoid, Necrolestes, and you can always spice up your art with a few details based on this wondrous creature.

However, it is nonetheless a very specialized animal. Comparing the “marsupial mole” to, say, Henkelotherium is like comparing a mole to a cat: it’s not going to work. So keep that in mind.

Necrolestes

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Necrolestes patagoensis skull and skeleton. Later image by Gabriel Lio.

Necrolestes is by far the best illustrated of all dryolestoids, thanks to it basically being a victorian paleontological meme. It is very similar to the still living “marsupial mole” – and almost certainly it’s closest relative if it is a dryolestoid – differing mostly in details of the head, with a strange up-turned snout and prominent fangs.

Like the “marsupial mole” it is too specialised to be a model for every dryolestoid however. For instance, although the Cretaceous south american Leonardus is closely related to it…

Cronopio

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…so is Cronopio, an entirely different animal altogether.

Armchair anatomists might find the above skull to resemble that of a pig, and that’s basically what Cronopio was: a tusked, long snouted omnivore, even edging on the size of small suines.

Many an online article compare this thing to Scrat, the saber-toothed squirrel from the Ice Age movies. However, from what we know it seemed to have been a terrestrial forager, and probably not particularly squirrel-like.

It is nonetheless not a very mole-like animal, unlike either Necrolestes or the “marsupial moles”.

Henkelotherium

What is squirrel like, however, is the Jurassic aged Henkelotherium, from my home country of Portugal.

This animal is completely unlike the previous ones: rather than being robust, it is very gracile, and rather than digging on the ground it lived on the tree canopy. In the Jurassic it seems virtually every mammal group had an arboreal representative (be it the docodont Agiloconodon, volaticotheres, haramiyidans or early therians, among others), and as it turns out dryolestoids were no exception.

Crusafontia

Another dryolestoid frequently depicted as arboreal and squirrel-like is Crusafontia; however, this is a holdover from when its remains were considered to belong to an early primate, and it’s probably impossible to confirm given that we only know it from a few jaws and teeth.

However, being a diverse group as it was, Dryolestoidea probably had several more arboreal species, and it’s certainly possible that many taxa we only know from teeth were in fact arboreal.

Dryolestes

Very few discussions are complete without the eponymous genera. Compared to other dryolestoids, Dryolestes itself is laughably underrepresented in so much as diagrams, but there a bit we can glean from the jaws we have.

For starters, by Jurassic mammal standards it was fairly large, being roughly the size of a hedgehog. It probably lived like one as well, judging its fairly generalized teeth yet robust jaws.

Keep in mind that we know some Mesozoic mammals had spines (i.e. Spinolestes) or otherwise crazy hair (Volaticotherium, with its long tail bristles), so it’s very likely dryolestoids were doing similar things. This is an aspect of mammalian paleoart that seriously needs exploring.

Mesungulatoids

(First two pictures belong to Peligrotherium. Last is a molar of Mesungulatum)

The most spectacular of all dryolestoids were probably the mesungulatoids, a herbivorous lineage that diversified during the Late Cretaceous of South America, and endured for a few million years into the Paleocene, achieving megafaunal sizes in the case of Peligrotherium.

Most frustratingly, they’re also the hardest to find good pictures of, as the most complete skull yet is available only on a paywalled paper.

In general, we know that these animals had blunt snouts, as the thick and up-turned jaws above can clue you in, packed with batteries of strange molars. In this regard maybe the also blunt skull of the “marsupial moles” might serve as a good reference.

And more

Austrotriconodon molar

Hopefully the above might have helped you get a basic picture of dryolestoid diversity and apparence.

Sources:

Kielan-Jaworowska, Zofia; Cifelli, Richard L; Luo, Zhe-Xi (2004). Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure. New York: Columbia University Press. ISBN 978-0-231-11918-4.

Agnolin, F.; Chimanto, N. (2014-12-22). Morphological evidence supports Dryolestoid affinities for the living Australian marsupial mole Notoryctes”. PeerJ Preprints. 2: e755v1. doi:10.7287/peerj.preprints.755v1.

Dental and Craniomandibular Anatomy of Peligrotherium Tropicalis: The Evolutionary Radiation of South American Dryolestoid Mammals, ProQuest, 2008

Guillermo W. Rougier, Sebastián Apesteguía and Leandro C. Gaetano (2011). Highly specialized mammalian skulls from the Late Cretaceous of South America”. Nature. 479: 98–102. doi:10.1038/nature10591.  Supplementary information

Gaetano, C. A. Marsicano, and G. W. Roughier. 2013. A revision of the putative Late Cretaceous triconodonts from South America. Cretaceous Research 46:90-100

One Comment leave one →
  1. January 9, 2017 2:30 am

    Most mammalian clades had arboreal representatives in the Jurassic.
    Couldn’t mammals be just ancestrally arboreal, or at least with ‘general purpose’ anatomy like many lizards today?

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