Radinskya and Mycrosyops move back to the Tillodontia in the LRT

These four taxa
little Radinskya, large Tillodon (Fig 1), little Microsyops and large Trogosus (Fig 2) now nest together in the LRT in the Tillodontia.

Radinskya is a traditional perissodactyl.
Microsyops is a traditional plesisadapiform.

The size disparity, bone fusion and missing elements kept these ‘wildcard’ taxa questionable. They remain questionable. These are currently in need of testing with a similar taxon list.

All are derived from Petaurus,
the flying phalanger, a gliding marsupial with rodent-like incisors in the early days of Diprotodontia. They are also all close to the clade that gave us the marsupial lion, Thylacoleo. Apatemys and koalas leading to wombats.

According to Wikipedia,
“Tillodonts have long been considered enigmatic and difficult to compare to living mammals. When Marsh (1875) 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.”

Based on the size disparity
(Figs 1,2) can the little taxa be considered juveniles of the larger taxa? Well, Radinskya is from the Paleocene of China. Tillodon is from the Eocene of North America. Micryosyops is from the Eocene of North America as is Trogosus.

So: inconclusive. There is phylogeny here. There might be ontogeny here.
This was a wide-ranging clade of marsupials, leaving descendants only in Australia, their refugium from the Jurassic onward when Gondwana began to split apart.

Evidently earlier I put these four taxa together,
based on the Trogosus page on ReptileEvolution.com, then tore them apart, then put therm back together. They have been difficult = headache taxa.

References
Gazin CL 1953. The Tillodontia : an early tertiary order of mammals”. Smithsonian Miscellaneous Collections. 121 (10): 1–110.
Leidy J 1871. Remains of extinct mammals from Wyoming. Proceedings of the Academy of Natural Sciences 23: 113–116.
Leidy J 1872. Remarks on fossils from Wyoming: Proceedings of the Academy of Natural Sciences, Philadelphia 1872: 19–21.
Marsh OC 1872. Preliminary description of new Tertiary Mammals. Parts I– IV: American Journal of Science 4: 122–128, 202–224.
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.
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.
Russell LS 1935. A middle Eocene mammal from British Columbia. American Journal of Science. 5. 29: 54–55.
Silcox MT, Gunnelll GF and Bloch JI 2020. Cranial anatomy of Microsyops annectens(Microsyopidae, Euarchonta, Mammalia) from the middle Eocene of Northwestern Wyoming. Journal of Paleontology, 28pp. 0022-3360/20/1937-2337
doi: 10.1017/jpa.2020.24

wiki/Trogosus 
wiki/Tillodon
wiki/Tillodontia
wiki/Radinskya
wiki/Microsyops