Periptychus compared to Mondodelphis for the first time

According to Wikipedia – Periptychus,
“Periptychus is an extinct genus of mammal belonging to the family Periptychidae. It lived from the Early to Late Paleocene and its fossil remains have been found in North America. This animal was of medium size and could exceed one meter in overall length; Periptychus is supposed to have weighed about 23 kilograms. The shape of the skull of Periptychus was almost identical to that of early Eutheria, although it was more robust.”

Figure 1. Paleocene Periptychus skull in three views to scale with extant Monodelphys, a close relative. ” data-image-caption=”

Figure 1. Paleocene Periptychus skull in three views to scale with extant Monodelphys, a close relative.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/periptychus-skull3views588.jpg?w=220″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/periptychus-skull3views588.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-89044″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/periptychus-skull3views588.jpg” alt=”Figure 1. Paleocene Periptychus skull in three views to scale with extant Monodelphys, a close relative.” width=”584″ height=”797″ />

Figure 1. Paleocene Periptychus skull in three views to scale with extant Monodelphys, a close relative.

Here
(Fig 1) the skull of Periptychus is compared to that of the transitional marsupial, Monodelphis domestica. The two now nest together in the large reptile tree (LRT, 2322 taxa, subset Fig 2) where the mammal subset of this large cladogram is now more clearly resolved.

That comes after 170 days of focused review and rescoring.

The mammals have finally become much more fully resolved.
That happened by rescoring taxa (= correcting earlier mistakes) and deleting two partial skull taxa: the basal tree shrew, Maelestes, and the giant narrow-skull tenrec, Andrewsiphius.

Still not perfect. Not fully resolved.

Figure x. Subset of the LRT focusing on Arsinoitherium relatives arising from Monodelphis, a marsupial. Added September 24, 2024. The derived taxa here were never considered marsupials in prior literature. ” data-image-caption=”

Figure x. Subset of the LRT focusing on Arsinoitherium relatives arising from Monodelphis, a marsupial. Added September 24, 2024. The derived taxa here were never considered marsupials in prior literature.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/arsinoitherium.relatives.588-1.jpg?w=254″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/arsinoitherium.relatives.588-1.jpg?w=584″ tabindex=”0″ role=”button” class=”size-full wp-image-88988″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/09/arsinoitherium.relatives.588-1.jpg” alt=”Figure x. Subset of the LRT focusing on Arsinoitherium relatives arising from Monodelphis, a marsupial. Added September 24, 2024. The derived taxa here were never considered marsupials in prior literature.” width=”584″ height=”690″ />

Figure 2. Subset of the LRT focusing on Arsinoitherium relatives arising from Monodelphis, a marsupial. Added September 24, 2024. The derived taxa here were never considered marsupials in prior literature.

The larger size of Periptychus
is a result of post-asteroid relief from dinosaur predation.

Periptychus carinidens
(Cope 1881; Shelley et al. 2018) was originally and later unable to determine closest relatives. Here it nests between tiny Monodelphis (Fig 1) and horned Arsinoitherium (Fig 2). The manus and pes are primitive in having no reduced fingers or toes, yet the unguals are reduced to stub-like round hooves.

Hooves developed independently in this marsupial clade. Since all derived taxa in this clade are extinct, I don’t know if a placenta developed independently for a fourth time in this clade with a single vagina = monodelphic (Fig 4) or not.

Neither Bemalambda nor Monodelphis
were mentioned in the text of a huge monograph by Shelley et al 2018. They wrote, “The anatomy of Periptychus is unique and lacks any extant analogue; it combines a basic early placental body plan with numerous unique specializations in its dental, cranial and postcranial anatomy that exemplify the ability of mammals to adapt and evolve following catastrophic environmental upheaval.”

Perhaps expanding the taxon list to include Bemalambda. Monodelphis and others (Fig 2) would have helped. The authors did make comparisons to Alcidedorbignya, Ectoconus and Pantolambda, three related taxa in the LRT (Fig 2). No phylogenetic analysis was published by Shelley et al.

References
Cope ED 1881. The Condylarthra (Continued). American Naturalist 84;18: 892–906.
Shelley SL, Williamson TE and Brusatte SL 2018. The osteology of Periptychus carinidens: A robust, ungulate-like placental mammal (Mammalia: Periptychidae) from the Paleocene of North America. PlosOne July 18, 2018. https://doi.org/10.1371/journal.pone.0200132

wiki/Periptychus
wiki/Arsinoitherium
wiki/Gobiatherium
wiki/Isectolophus
wiki/Bemalambda
wki/Orthaspidotherium
wiki/Pholidocercus