Let's face it, there's an extraordinary number of fairly obscure Paleogene artiodactyl groups that are only familiar if you're a specialist. I've recently had the enjoyable task of writing about all of them for a major in-progress book project (details to come), and today I'd thought I'd share text on one - just one - of those fairly obscure groups. My apologies to the authors who work on these animals and consider them dear friends rather than obscure oddballs. Anyway...

Amphirhagatherium model constructed, I think, by Jörg Erfurt and Hans Altner; image by DagdaMor, licensed under Creative Commons Attribution 3.0 Unported license.

Choeropotamids are one of several anthracothere-like groups from the European Eocene and Oligocene, mostly known from jaws and teeth [image above by DagdaMor]. Oh, what are anthracotheres? Anthracotheriids or anthracotheres are an Eocene-Pleistocene group of suiform-like artiodactyls, often imagined as hippo prototypes and frequently implicated in hippopotamus ancestry. Note that anthracotheres are not to be confused with anthracobunids, a group of tethytheres close to sirenians and/or proboscideans.

Several choeropotamid taxa were originally included within Anthracotheriidae but the realisation that the taxa concerned are united by a distinctive pattern of premolar dentition led to the idea that they should be included within a new group termed Haplobunodontidae, named in 1941. Haplobunodontidae was eventually shown to be synonymous with Choeropotamidae, named by Richard Owen in 1845 (Hooker & Thomas 2001). Key features used to unite choeropotamids include an incisiform lower canine, a short diastema between the first and second lower premolars, and bunoselenodont* molars (Hooker & Thomas 2001). Tooth form indicates that choeropotamids ate fruit and leaves (an idea supported by gut contents known for Masillabune from Messel) with the caniniform anterior teeth at least suggesting the possibility of occasional faunivory.

* This means that the molars combine both mound-shaped (= bunodont) cusps as well as the semi-lunate (= selenodont) cusps.

Excellent skulls of the late choeropotamid Tapirulus from Quercy, France, from Costeur & Berthet (2011).

Jörg Erfurt and Hans Altner's Amphirhagatherium model again, this time with a prototype that lacks the final integument; note also the conference poster in the background. Photo by Darren Naish.

Later members of the group (like Lophiobunodon and Tapirulus) have more selenodont teeth and hence are likely to have been more dedicated to herbivory. Thick enamel in Choeropotamus suggests that it fed on thick-skinned fruit. Cuisitherium from the Ypresian of France is the oldest choeropotamid and Amphirhagatherium from the upper-most Eocene or lower-most Oligocene of Germany is the youngest. Increasing seasonality and cooler climates at the end of the Eocene may have caused the extinction of this mostly northern European group.

We have a reasonably good idea of what live choeropotamids might have looked like thanks to the nice specimens from Messel. A really good life-sized, accurate model of Amphirhagatherium is displayed at the Institute of Geosciences at Martin-Luther-University, Halle-Wittenberg, Germany and is shown here. I believe that it was constructed by Jörg Erfurt and Hans Altner (I may be wrong!), and its construction and appearance are described in Erfurt & Altner (2003). I've seen the model myself at conferences and have even photographed it. Can I find those photos right now? No, but I'll add them here when I do [UPDATE: found them, obviously].

For previous Tet Zoo articles on artiodactyls, see...

Refs - -

Costeur, L. & Berthet, D. 2011. A new skull of Tapirulus from the late Eocene of France. In Lehmann, T. & Schaal, S. F. K. (eds) The World at the Time of Messel: Puzzles in Palaeobiology, Palaeoenvironment and the History Early Primates. Senckenberg Gesellschaft für Naturforschung, pp. 40-41.

Erfurt, J. & Altner, H. 2003. Habitus-Rekonstruktion von Anthracobunodon weigelti (Artiodactyla, Mammalia) aus dem Eozän des Geiseltales. Veröffentlichungen des Landesamtes für Archäologie 57, 153-175.

Hooker, J. J. & Thomas, K. M. 2001. A new species of Amphirhagatherium (Choeropotamidae, Artiodactyla, Mammals) from the Late Eocene Headon Hill Formation of southern England and phylogeny of endemic European ‘anthracotherioids’. Palaeontology 44, 827-853.