Trogosus, the tillodont, is a giant tree shrew!

Figure 1. Trogosus, the tillodont, shown from two different illustrations.

Figure 1. Trogosus, the tillodont, shown from two different illustrations.

Pretty obvious
when you put the two of them together. Tupaia is a regular tree shrew. Trogosus (Leidy 1871) is a really big one as recovered by the large reptile tree (to be updated this weekend).

Figure 2. Tupaia, the tree shrew. Note the many similarities here to the much larger Trogosus (Fig. 1).

Figure 2. Tupaia, the tree shrew. Note the many similarities here to the much larger Trogosus (Fig. 1).

Over the past five years
the large reptile tree created new clades among basal reptiles. Now it’s deleting and combining clades within the Mammalia. Today we’ll talk about Trogosus castoridens (“beaver-toothed gnawing-hog”, Fig. 1), a purported member of the Tillodontia (Early Paleocene to Late Eocene). This is just one more overlooked taxonomic sister relationship recovered by the large reptile tree (745 taxa).

Wikipedia considers tillodonts
close to Pantodonta (Pantolambda and kin), which are similar in size.

By contrast, the large reptile tree
nests the largest tillodont, Trogosus, between Tupaia (living tree shrew*, Fig. 2) + Apatamys (extinct apatemyed) and Plesiadapis (former basal primate) + rabbits (including Plesiadapis, which is NOT a primate). Trogosus had a 37cm skull, so it was the size of a bear.

Re: tillodonts, OC Marsh 2013 wrote:
“These animals are the among the most remarkable yet discovered in American strata, and seem to combine characters of several distinct groups, viz: Carnivores, Ungulates, and Rodents. In Tillotherium (=Trogosus), the type [specimen] of the order, the skull has the same general form as in the Bears, but its structure resembles that of Ungulates. The molar teeth are of the ungulate type, the canines are small, and in each jaw there is a pair of large scalpiform incisors faced with enamel, and growing from persistent pulps, as in Rodents.”

As in rodents, indeed!
Rodents and Insectivores arise from these basal taxa.

References
Leidy J 1871. Remains of extinct mammals from Wyoming. Proceedings of the Academy of Natural Sciences 23: 113–116.
Marsh OC 1875. New Order of Eocene Mammals. American Journal of Science 9: 221

*The two tree shrews
tested in the large reptile tree, Tupaia and Ptilocercus (Fig. 3), are not related to one another. The former is closer to rabbits. The latter is closer to flying lemurs and bats in the LRT. It’s a testimony to the LRT that it can split the two tree shrews that others lump together while lumping the giant Trogosus with little Tupaia.

Ptilocercus, pen-tailed tree shrew

Figure 2. Ptilocercus, pen-tailed tree shrew, a living relative to the ancestor of bats and colugos.

 

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