A small tapir-like ‘oreodont’ from North America enters the LRT with astrapotheres from South America

This could be an overlooked interrelationship.
The large reptile tree (LRT, 1978+ taxa; Fig. 4) currently nests North American tapir-like Brachycrus (Figs. 1–3) with a similar, though much larger South American tapir-like taxon, Astrapotherium (Fig. 1).

Figure 1. Astrapotherium to scale with the smaller Brachycrus and transitional Astraponotus.

According to Wikipedia,
Brachycrus is an extinct genus of oreodont, of the family Merycoidodontidae, endemic to North America.”

According to Wikipedia,
Astrapotherium (“lightning beast”) is an extinct genus of South American mammals that… was unrelated to elephants or tapirs, but was instead related to other extinct South American ungulates.”

According to the LRT, neither is correct.

Figure 2. Brachycrus skull in several views.

Also added to the LRT
is the Brachycrus-sized transitional astrapothere, Astranopodus (Figs 1, 3).

Figure 3. Astraponotus skull in 3 views to scale with Brachycrus.
Figure 3. Astraponotus skull in 3 views to scale with Brachycrus.

Astrapotherium magnum
(Burmeister 1879, Hatcher 1901; Paleocene-Miocene, 59-12 mya; 3m long; Fig. 1) was considered a South American ungulate and a member of the order, Astrapotheria, by the authors of Wikipedia. They report, “The history of this order is enigmatic.” Here (Fig. 4) Astrapotherium nests with Meniscotherium, in a clade between Titanoides and Phenacodus. Like a hippo, the large and ever-growing curved canines of Astrapotherium scraped against each other during life producing sharp tips. Uniquely, the rostrum was much shorter than the mandible. The feet and toes were all small. The narial opening was elevated to the top of the skull. Astrapotherium likely had a tapir-like trunk.

Brachycrus laticeps
(origiginally Merycochoerus Douglass 1900; CM796; Miocene, 14mya; 1m long) was considered an North American oreodont with a tapir-like trunk and deep jaws. Here it nests with South American Astrapotherium. Both are derived from North American Meniscotherium.

Astraponotus assymemetrum
(Ameghiino 1901; Late Eocene 35mya) is a transitional South American taxon between Astropotherium (Fig. 1) and Brachycrus (Figs. 1–3).

We looked at tiny Trigonostylops earlier here. and Meniscotherium earlier here.

Figure 4. Subset of the LRT focusing on Astrapotherium and kin.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a prior citation so I can promote it here.

You probably noticed
the pace of posts has picked up in the last day or two. That’s because it is now Abstracts Season and there is a backlog to get through. That will continue until that drains down a bit. Thank you for your readership, your comments and your continuing interest in paleontology.

Ameghino F 1901. Notices préliminaires sur des ongulés nouveaux des terrains crétacés de Patagonie [Preliminary notes on new ungulates from the Cretaceous terrains of Patagonia]. Boletin de la Academia Nacional de Ciencias de Córdoba 16:349-429.
Burmeister 1879. Description physique de al République Agentine, T. III 1879:517.
Douglass E 1900. New species of Merycochoerus in Montana. Part I. American Journal of Science 10(60):428-438.
Hatcher JB 1901. Report of the Princeton University Expeditions to Patagonia 1869-1899. Mammalia of the Santa Cruz Beds. IV. Astrapotheria. Scott WB ed. Vol. 6, Paleontology 3. Princeton, NJ Stuttgart 1909-1928.


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