The prehensile hand and foot of Caluromys

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

Figure 1. Pteropus and Caluromys compared in vivo and three views of their skulls. Caluromys is in the ancestry of bats and shows where they inherited their inverted posture.

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.

Figure 1. Caluromys hand and foot from Argot 2002 compared to Didelphis and repaired here to match.

Figure 2. Caluromys hand and foot from Argot 2001, 2002 compared to the pes of Didelphis. The manus and pes of primates, tree shrews (in Glires) and basal arboreal Carnivorans all arise from Caluromys. These demonstrate the early appearance of the prehensile/opposable big toe and thumb, derived from the semi-opposable big toe of Didelphis, the Virginia opossum and even more so in Caluromys. 

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.

References
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.

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