Mesonyx: hippo sister, baleen whale ancestor

Since this post, about 500 taxa have been added to the LRT. Some of them split odontocetes + tenrecs from mysticetes + mesonychids (through hippos and desmostylians).

The wolf-sized mammal,
Mesonyx uintensis (Cope 1872; Late Eocene, 50mya; 42 cm cranium length) looks like a hooved predator, and maybe it was. But Mesonyx nests between herbivores and those big canines are also found in its sister, Hippopotamus, according to results recovered from the large reptile tree (740 taxa and growing).

Figure 1. Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater.

Figure 1. Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater.

Mesonyx was a mesonychid and an even-toed ungulate (artiodactyl).
Andrewsarchus, traditionally considered a giant mesonychid, is not related, as we learned earlier (contra Osborn 1924). The legend of Andrewsarchus and its purported relationship to Mesonyx is where the whale/artiodactyl hypothesis had its origin. Analysis has invalidated that hypothesis (contra Spaulding et all 2009), but supports the odontocete /tenrec hypothesis of which Andrewsarchus remains a part as a giant tenrec.

I hope you’re concerned about the state of
systematics within vertebrate paleontology at present. In 2016 there should not be this many problems with traditional tree topologies and individual taxa. If an amateur working from unfamiliar online images is able to piece together a tenable topology of reptile (plus mammal and bird) relationships different from and more logical than traditional topologies, then there’s a problem out there. Students put their faith in what they read in textbooks. They get better grades when they are able to repeat what they’ve read. Manuscripts get approved if they follow dogma. As scientists, however, we need to test assertions, especially those hypotheses of relationships that many agree are flimsy.

Osborn HF 1924. Andrewsarchus, giant mesonychid of Mongolia. American Museum Noviattes 146: 1-5.
Spaulding M, O’Leary MA, Gatesy J 2009. Relationships of Cetacea (Artiodactyla) Among Mammals: Increased Taxon Sampling Alters Interpretations of Key Fossils and Character Evolution. PLoS ONE 4(9): e7062. doi:10.1371/journal.pone.0007062



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