Paleocene Orthaspidotherium now nests with Eocene Meniscotherium

In members of this clade
of early herbivorous placental mammals the lacrimal (tan) overlaps the jugal (cyan), the postparietal is longer than then parietal and the posterior premolars have a molar-like morphology.

According to Wikipedia,
“Orthaspidotherium was a European Paleocene genus of early herbivorous mammals of the family Pleuraspidotheriidae. It was included in the family Meniscotheriidae by Teilhard de Chardin in 1921-1922 and was subsequently separated into the family Pleuraspidotheriidae, before being placed in the family Phenacodontidae. The first complete skull of O. edwardsi was described in 2010, and the same paper once again places it in Pleuraspidotheriidae.”

According to Wikipedia,
“Meniscotherium is an extinct genus of dog-sized mammal which lived 54–38 million years ago. It was a herbivore and had hooves. Fossils have been found in Utah, New Mexico. and Colorado. Many individuals have been found together, indicating that it lived in groups. Body mass in M. chamense is estimated to be 5–17 kg, making it about the size of a small dog. A 2014 cladistic analysis places it within stem perissodactyls.

Figure 1. Top: Meniscotherium. Bottom: Orthaspidotherium to scale. ” data-image-caption=”

Figure 1. Top: Meniscotherium. Bottom: Orthaspidotherium to scale.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/meniscotherium588.jpg?w=146″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/meniscotherium588.jpg?w=498″ tabindex=”0″ role=”button” class=”size-full wp-image-88561″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/meniscotherium588.jpg” alt=”Figure 1. Top: Meniscotherium. Bottom: Orthaspidotherium to scale. ” width=”584″ height=”1202″ />

Figure 1. Meniscotherium and Orthaspidotherium to scale and shown full scale on 72dpi monitors. Note the lacrimal (tan) layered over jugal (cyan).

In addition
Hypsodus (Fig 3) and Amphicynon major (Fig 4) are here revised with new DGS colors and rescored accordingly, now nesting with the above two taxa.

Figure 3. Hypsodus revised in 2024. ” data-image-caption=”

Figure 3. Hypsodus revised in 2024.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/hyopsodus-overall588.jpg?w=140″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/hyopsodus-overall588.jpg?w=477″ tabindex=”0″ role=”button” class=”size-full wp-image-88567″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/hyopsodus-overall588.jpg” alt=”Figure 3. Hypsodus revised in 2024. ” width=”584″ height=”1253″ />

Figure 3. Hypsodus revised in 2024 with an overlapping lacrimal (tan) on the cheekbone. Note the long torso and short limbs.

Hypsodus is a traditional relative
of Meniscotherium. ?Amphicyon major (Fig 4) is not.

Hyopsodus lepticus
(H. paulus type, Leidy 1870; Late Eocene, 56-45 mya; ~20 cm in length; AMNH 143783) was originally considered a condylarth or a perissodactyl, an odd-toed ungulate, despite having a five-clawed manus and a four-clawed pes. Three molars are present.

Figure 4. Amphicyon major is a traditional bear dog. Here it nests among the clawed condylarths close to Hyopsodus in figure 3. ” data-image-caption=”

Figure 4. Amphicyon major is a traditional bear dog. Here it nests among the clawed condylarths close to Hyopsodus in figure 3.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/amphicyon_major_skull588.gif?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/amphicyon_major_skull588.gif?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-88571″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/amphicyon_major_skull588.gif” alt=”Figure 4. Amphicyon major is a traditional bear dog. Here it nests among the clawed condylarths close to Hyopsodus in figure 3.” width=”584″ height=”389″ />

Figure 4. Amphicyon major is a traditional bear dog. Here this specimen nests among the clawed condylarths close to Hyopsodus in figure 3. Broken cheeckbone (zygomatic arch) repaired here in sold DGS colors.

Figure 5. Hyopsodus skeleton compared to the larger, later Amphicyon major.

Housekeeping like this
continues. Because the LRT includes so many taxa, getting back to review all of them takes a little time.

References
Blainville H 1841. Osteographie et description iconographique comparée du squelette et du systéme dentaire des cinq classes d’animaux vertébrés récents et fossiles. Vol. 6, Carnassiers. Paris: Arthus Bertrand.
Cooper LN, Seiffert ER, Clementz M, Madar SI, Bajpai S, Hussain ST, Thewissen JGM 2014-10-08. Anthracobunids from the Middle Eocene of India and Pakistan Are Stem Perissodactyls. PLoS ONE. 9 (10): e109232. doi:10.1371/journal.pone.0109232. PMID 25295875.
Cope ED 1872. Descriptions of some new Vertebrata from the Bridger Group of the Eocene. Proceedings of the American Philosophical Society 12:460-465.
Cope ED 1874. Report of the Chief of Engineers for. 1874 Vol. II, Pt. II, Appendix FFa of Appendix FF, pp. 115-130.
Ladevèze S, Missiaen P and Smith T 2010. First Skull Of Orthaspidotherium Edwardsi (Mammalia, “Condylarthra”) From The Late Paleocene Of Berru (France) And Phylogenetic Affinities Of The Enigmatic European Family Pleuraspidotheriidae. Journal of Vertebrate Paleontology 30(5): 1559–1578.
Leidy J 1869. Extinct Mammals of Dakota and Nebraska:Including an account of some allied forms from other localities, together with a synopsis of the mammalian remains of North America., Journal of the Academy of Natural Sciences, Philadelphia 2(7): 135–141.
Leidy J 1870. Remarks on a collection of fossils from the western territories. Proceedings of the Academy of Natural Sciences of Philadelphia 22: 109–110.
Williamson TE and Lucas SG 1992. Meniscotherium (Mammalia, “Condylarthra”) from the Palaeocene-Eocene of Westeran North America. New Mexico Museum of Natural Hstory and Science Bulletin 1.

wiki/Meniscotherium
wki/Orthaspidotherium
wiki/Amphicyon
wiki/Hyopsodus