I could not find
and still cannot find a complete skeleton for Caluromys (Fig. 1), the transitional marsupial leading to placentals. Argot 2001 published images of the hand in vivo. Argot 2002 published images of the foot in vivo and as an incomplete set of bones (Fig. 2). I matched those bones to the foot, still wishing I had all the bones, as in an X-ray.
The prehensile manus and pes of Caluromys
is primitive for the Eutheria (= Placentalia). From these arise the wings of bats, the flippers of whales, the hooves of horses as well as the fingers I just used to type this sentence.
Argot C 2001. Functional-Adaptive Anatomy of the Forelimb in the Didelphidae, and the Paleobiology of the Paleocene Marsupials Mayulestes ferox and Pucadelphys andinus. Journal of Morphology 247:51–79.
Argot C 2002. Functional-adaptive analysis of the hindlimb anatomy of extant marsupials and the paleobiology of the Paleocene marsupials Mayulestes ferox and
Pucadelphys andinus. Journal of Morphology 253:76–108.