Enigmatic Radinskya nests as a small sea cow in the LRT

This has been a tough taxon to nest.
Paleocene Radinskya (Fig 1) has puzzled palenotologists since its description in McKenna et al 1989. Earlier the LRT nested Radinskya closer to the base of elephants than to sea cows. Now that hypothesis has been refined.

Figure 1. Left: Paleocene Radinskya in 3 views. Right: Radinskya to scale with Eocene Prorastomus, a quadrupedal sea cow. ” data-image-caption=”

Figure 1. Left: Paleocene Radinskya in 3 views. Right: Radinskya to scale with Eocene Prorastomus, a quadrupedal sea cow.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/prorastomus-radinskya-skulls588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/prorastomus-radinskya-skulls588.jpg?w=584″ class=”size-full wp-image-86649″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/06/prorastomus-radinskya-skulls588.jpg” alt=”Figure 1. Left: Paleocene Radinskya in 3 views. Right: Radinskya to scale with Eocene Prorastomus, a quadrupedal sea cow.” width=”584″ height=”426″ />

Figure 1. Left: Paleocene Radinskya in 3 views. Right: Radinskya to scale with Eocene Prorastomus, a quadrupedal sea cow. Note the split nasals + frontal contact to naris.

According to Wikipedia – Radinskya:
“it shares many characters with perissodactyls and some with phenacolophids, but is too primitive to be called either a horse, a rhino, or a tapir. Radinskya is known only from a partial skull and upper dentition, which makes it difficult to assess its relationships to other fossils.”

Suggestion: test a wider gamut of taxa to resolved this enigma.

Here
in the large reptile tree (LRT, 2320 taxa) Radinskya now nests with Prorastomus, and Sobrarbesiren cariedli, two Eocene qudrupedal sea cows, which are still close to the trunk-less ancestors of elephants, like Moeritherium. All three frequented swamps.

Radinskya yupingae
(McKenna et al. 1989, Holbrook 2014; IVPP V-5255; Middle Paleocene; China) was originally considered a perissodactyl-like herbivore, but never with confidence. Here Radinskya nests between Ectocion and Procavia, at the base of the elephant clade. Note the tiny procumbent second incisor. Missing are the large procumbent medial incisors. Like Procavia the tabulars contact one another medially, posterior to the central postparietal. The premolar is almost molar-like in appearance.

Sobrarbesiren cariedli
(Díaz-Berenguer 2018; Eocene, 47mya) is a basal sirenian with four legs, a short tail and teeth. The anterior dorsals are taller and the pelvis is longer. The caudal vertebrae have ventral processes. The cervicals are shorter. The forelimbs are larger than the hind limbs.

References
McKenna MC, Chow M, Ting S and Luo Z 1989. Radinskya yupingae, a perissodactyl-like mammal from the late Paleocene of China. In Prothero DR, Schoch RM The evolution of perissodactyls. Oxford monographs on geology and geophysics. 15. New York: Oxford

wiki/Radinskya

Traditional Oligocene bear, Amphicynodon, now basal to elephants