Uintatherium nests with the ungulates in the LRT

At present,
the large reptile tree (LRT) has been growing for five years. In all that time the tree topology has not exchanged branches very often. Instead it continue to grow like a real tree, adding leaves between existing branches and nodes.

Adding mammals comes with a new set of risks
because mammals are often identified by their teeth. The LRT does not include mammal tooth traits, so mammals are nested by the same traits as other reptiles here.

Figure 6. Uintatherium overall. Note the postcranial similarities with Arsinoitherium.

Figure 1. Uintatherium overall.

The latest additions include
the traditional condylarths, Phenacodus and Uintatherium, along with the pantodont, Alcidedorbignya (Fig.1). It may be by convergence, or it may be an echo of actual evolutionary events, but Phenacodus nests at the bnase of the present list of herbivores, including ungulates and elephant (Elephas) + hyrax (Procavia). The aardvark (Orycteropus) is the proximal outgroup. Uintatherium nests at the base of the ungulates, like a robust five-toed deer. Uintatherium also has the short toes of an elephant.

Figure 2. Uintatherium skull with bones tentatively identified. I have found no data online to support or refute these tracings. Note the shifting of the mandible to the invivo position, where the jaw joint is correct and the teeth are better aligned. The premaxilla appears to extend like a laminate over the maxilla.

Figure 2. Uintatherium skull with bones tentatively identified. I have found no data online to support or refute these tracings. Note the shifting of the mandible to the invivo position, where the jaw joint is correct and the teeth are better aligned. The premaxilla appears to extend like a laminate over the maxilla.

 

I wonder
if mammal phylogeny is more simple that traditionally portrayed? The nesting of Uintatherium with fanged deer and fangless giraffes and derived from a sister to Phenacodus is not a fluke. There are very few traits in Uintatherium that do not appear in these closest relatives.

Likewise
the pantodont, Alcidedorbignya, nests at the base of PantolambdaEctoconus. In addition to teeth, the pattern of arterial and nerve openings in the skull are used in traditional cladograms, along with other details on other bones.

Wikipedia considers pantodonts to be herbivores. However de Muizon et al. 2015 report that “Pantodonts are generally large-sized herbivorous to omnivorous mammals from the Palaeogene, Pantodonts are traditionally diagnosed by a distinctive dental synapomorphy, the double V-shaped morphology of the upper premolars, a character that has not been observed so far in other eutherians.”

de Muizon et al. note that their Alcidedorbignya dates from 65 mya, just after the asteroid collision. “It was a moderately agile, plantigrade, generalized terrestrial mammal with good climbing ability (scansorial) and occasionally capable of standing in a bipedal position. The scutiform ungual phalanges were probably bearing nail-like hooves (or primate-like nails) and because of the absence of claws, fossorial habits are unlikely.”

Figure 3. Alcidedorbignya skull about full scale at 72 dpi screen resolution. Select bones are colorized.

Figure 3. Alcidedorbignya skull about full scale at 72 dpi screen resolution. Select bones are colorized.

de Muizon et al
did a fantastic job of extricating, describing and reassembling Alcidedorbignya. They perfumed CT scans, traced vein paths and performed a large gamut phylogenetic analysis that the large reptile tree cannot, at present, compete with.

Figure 5. Alcidedorbignya bones remarkably complete for the Paleocene, 65 mya and remarkable prepared.

Figure 5. Alcidedorbignya bones remarkably complete for the Paleocene, 65 mya and remarkable prepared. Scale bar is 2 cm or about half the in vivo size. This is a small pantodont.

References
Muizon C de, Billet G, Argot C, Ladevèze S & Goussard F 2015. Alcidedorbignya inopinata, a basal pantodont (Placentalia, Mammalia) from the early Palaeocene of Bolivia: anatomy, phylogeny and palaeobiology. Geodiversitas 37 (4): 397-634.

 

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