Eocene Tillodon enters the LRT as another giant tree shrew

A taxon rarely mentioned in the literature is
Tillodon (Fig 1). There is a reason for this. Evidently Tillodon and the Tillodontia have been traditional  enigmas according to several authors.

Figure 1. Tillodon skull in 3 views from Gazin 1953. Colors added here. ” data-image-caption=”

Figure 1. Tillodon skull in 3 views from Gazin 1953. Colors added here.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodon.skull_.3views588.jpg?w=178″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodon.skull_.3views588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87005″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodon.skull_.3views588.jpg” alt=”Figure 1. Tillodon skull in 3 views from Gazin 1953. Colors added here.” width=”584″ height=”985″ />

Figure 1. Tillodon fodiens skull in 3 views from Gazin 1953. Colors added here. The canine is absent. The overbite is impressive.

OC Marsh 1875 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.”

After several decades…

Gazin 1953 wrote,
“The Tillodontia is an order of mammals comprising a relatively small number of forms, distinctive in character, obscure in origin, and of seemingly short duration in geologic time. The oldest of these known are Clark Fork or upper Paleocene in age, and no forms in the earlier stages of the Paleocene can be surely identified as ancestral. Since Cope’s death the literature of vertebrate paleontology shows a dearth of references to the tillodonts, with very few contributions to our knowledge of this order.”

After several decades…

Gingerich and Gunnell 2006 wrote,
“What other orders of mammals tillodonts are most closely related to remains an open question. Esthonyx and its allies may have originated from Condylarthra, Anagalida, or Pantodonta, but until this question is resolved they are appropriately retained in a separate order, Tillodontia. Cope (1874) apparently first regarded Esthonyx as a North American member of the Toxodontia, but he later included it in the order Insectivora because of similarities shared with Erinaceus, while also noting resemblances to Creodonta and Primates. Van Valen went so far as to include Tillodontia as a suborder of Condylarthra.”

Figure 1. Tillodon, the original tillodont, enters the LRT at the base of Glires alongside Trogosus. ” data-image-caption=”

Figure 1. Tillodon, the original tillodont, enters the LRT at the base of Glires alongside Trogosus.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodon588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodon588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-86994″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodon588.jpg” alt=”Figure 1. Tillodon, the original tillodont, enters the LRT at the base of Glires alongside Trogosus.” width=”584″ height=”358″ />

Figure 2. Tillodon, the original tillodont, enters the LRT at the base of Glires alongside Trogosus.

According to Wikipedia – Tillodontia
“Tillodontia is an extinct suborder of eutherian mammals known from the Early Paleocene to Late Eocene of China, the Late Paleocene to Middle Eocene of North America where they display their maximum species diversity, the Middle Eocene of Pakistan, and the Early Eocene of Europe. Leaving no descendants, they are most closely related to the pantodonts, another extinct group. The tillodonts were medium- to large-sized animals that probably fed on roots and tubers in temperate to subtropical habitats. Tillodonts had rodent-like incisors, clawed feet and blunt, cusped teeth. They were mostly medium-sized animals, although the largest of them (such as Trogosus) could reach the size of a large bear.”

See figure 5.

Figure 2. Tillodontia in the LRT. Comparable clades mentioned by Marsh are also highlighted. ” data-image-caption=”

Figure 2. Tillodontia in the LRT. Comparable clades mentioned by Marsh are also highlighted.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodontialrt588.jpg?w=95″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodontialrt588.jpg?w=326″ tabindex=”0″ role=”button” class=”size-full wp-image-87003″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/tillodontialrt588.jpg” alt=”Figure 2. Tillodontia in the LRT. Comparable clades mentioned by Marsh are also highlighted.” width=”584″ height=”1835″ />

Figure 3. Tillodontia in the LRT. Comparable clades mentioned by Marsh 1876 are also highlighted. Tillodontia nests close to the radiation of all placental clades, which esplains why prior authors wondered what they were. The LRT tests all candidates.

When Marsh first named and described the tillodonts, he explained:
“These animals are 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 Marsh [=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 scalpriform incisors faced with enamel, and growing from persistent pulps, as in Rodents.”

Figure 5. Two small extant traditional tree shrews, Tupaia and Ptilocercus. ” data-image-caption=”

Figure 5. Two small extant traditional tree shrews, Tupaia and Ptilocercus.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2021/06/ptilocercus_tupaia2scale588-1.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2021/06/ptilocercus_tupaia2scale588-1.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-56457″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2021/06/ptilocercus_tupaia2scale588-1.jpg” alt=”Figure 5. Two small extant traditional tree shrews, Tupaia and Ptilocercus.” width=”584″ height=”316″ />

Figure 4. Two small extant traditional tree shrews, Tupaia and Ptilocercus. Total length in Tupaia is about the length of the Tillodon skull alone, so these two are shown to scale with figures 1 and maybe 2.

In the LRT
(subset figure 3) Tillodon joins Trogosus (Fig 6) close to extant tree shrews like Tupaia and Ptilocercus (Figs 4, 6). A few days ago coyote-sized Protictitherium also joined the tree shrews, so larger taxa are beginning to arise more directly from the tree shrews.

Figure 1. Bear-sized Trogosus, the tillodont, shown to scale with tiny Ptilocercus. ” data-image-caption=”

Figure 1. Bear-sized Trogosus, the tillodont, shown to scale with tiny Ptilocercus.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/trogosus_skulls588.jpg?w=213″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/trogosus_skulls588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-87009″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/trogosus_skulls588.jpg” alt=”Figure 1. Bear-sized Trogosus, the tillodont, shown to scale with tiny Ptilocercus.” width=”584″ height=”821″ />

Figure 5. Bear-sized Trogosus, the tillodont, shown to scale with tiny Ptilocercus.

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

References
Gazin CL 1953. The Tillodontia : an early tertiary order of mammals”. Smithsonian Miscellaneous Collections. 121 (10): 1–110.
Marsh OC 1875. New Order of Eocene Mammals. American Journal of Science. 9: 221.
Marsh OC 1876. Principal characters of the Tillodontia, Part i. Amer. Journ. Sci. and Arts, vol. 11, pp. 249-251, i fig., pis. 8-9.

wiki/Tillodon – not yet posted
wiki/Tillodontia

Trogosus, the tillodont, is a giant tree shrew!