New data for the old skull of Mesonyx

…and, not surprisingly, the teeth are worn flat,
like those of an old hippo (Fig 1). Ever since Mesonyx entered the large reptile tree (LRT, 2044 taxa) it nested close to the genus, Hippopotamus, an extant herbivore, in a large clade of derived large placental herbivores that give birth to precocial young — rather than the more primitive clade of smaller placental omnivores, insectivores and carnivores with altricial (= helpless, underdeveloped) young to which we belong.

Figure 1. Engravings of Mesonyx. Colors and animation added here. Note the worn teeth, typical of an older (more mature or close to death) herbivorous mammal.

Wikipedia reports,
“They were probably active hunters.”

That’s a traditional myth,
according to phylogenetic bracketing and those worn down molars in figure 1.

Five years ago
the good folks at were a little upset that the LRT nested Mesonyx with Hippopotamus, suggesting (via phylogenetic bracketing) that Mesonyx, “was a plant eater.” If you go to that PaleoFails site you’ll see the data used for Mesonyx in 2016: a skull with unworn multicusp molars (or see Fig. 2 below). Unfortunately that was the only data that had crossed my path until now. Finding more detailed data sporting worn teeth (Fig. 1) further cements the hypothesis of mesonychid herbivory. presents
“The best in failing miserably at palaeontology.”

In 2016 PaleoFails reported mesonychid herbivory
was a miserable fail at paleontology.

Unfortunately, that ‘miserable fail’
was widely ‘liked’ by dozens of pseudonymous readers at Paleofails. And that’s okay. They were holding tight to their traditions in the face of a novel heresy. As Yale professor John Ostrom lamented, it takes time and rafts of evidence (Fig. 1) to change minds in paleontology.

Some quotes from Paleofail readers follow:
synapsidgirl reblogged this from jurassicsunsets and added:
Somebody. Please. Stop. Him. I mean, seriously, how can anyone look at that dentition and go “That there is a herbivore…

As mentioned above, phylogenetic bracketing with herbivores infers an herbivorous diet in fossil taxa. It’s a standard method in science. Synapsidgirl joins PhD Darren Naish, amateur paleontologist Mickey Mortimer and videographer, Dino Diego, in their urge to cancel novel ideas coming out of here.

jurassicsunsets reblogged this from palaeofail and added:
Mesonyx was a mammal, not a reptile. Its taxonomic position is a bit unclear, but it probably wasn’t sister to hippos,…

Thanks for clearing that up, Jurassicsunsets.

justgilbertianthings reblogged this from palaeofail and added:
I have no words for this

Someone, please hurry! Offer this pseudonym a hankie, a lawn chair and a lemonade.
: – )

For those of you who seriously want to become a paleontologist,
achieving infamy and a dose of vilification from pseudonyms and PhDs is (regrettably) going to part of the process when you discover something that upsets the established sense of order. Just be ready for it.

If you have a beef with someone’s hypothesis,
don’t come to battle with your emotions, a smidgen of outrage and an urge to cancel. Grow up. Wipe your tears. Be professional. Come to battle with your own cladogram, fresh data and an urge to help your colleague get back on the right track. Phylogenetic analysis works. So does phylogenetic bracketing, both for professional and all other scientists.

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 2. The graphic and caption that earned a place of dishonor at PaleoFails: “Mesonyx, the first known mesonychid was a sister to Hippopotamus in the large reptile tree. So maybe it was a plant eater.”

Mesonyx obtusidens
(Cope 1872, Eocene, 51 mya, 1.5m long, YPM VP 013066) Widely considered a carnivore, Mesonyx had the same large, dull, canine fangs also found in Hippopotamus, an extant herbivore. Mesonychids have been linked to whales, but toothed whales like Maiacetus are desendants of tenrecs. Baleen whales are descendants of oreodonts, Mesonyx. hippos, anthracobunids and desmostylians in that order.

Cope ED 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12:460-465.


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