Abstract:
Mesocyon temnodon is an Oligocene canid species that existed in localities such as South Dakota, North Dakota, Wyoming, Colorado, and Nebraska approximately 35.4 million years ago. Even though its evolutionary relationships and phylogenetic position are uncertain, it is known to be a member of the subfamily Hesperocyoninae, near the base of the canid evolutionary tree. Recent observations of Mesocyon temnodon fossils show that the ancient dog may have some anatomical similarities to feline specimens, especially in post-cranial samples. The presence of epicondylar fossae and the potential for retractable claws are two points of common morphology with felines. The purpose of this study was to evaluate claws from Mesocyon temnodon specimen NDGS 64 in order to determine the plausibility of retraction. This process was executed utilizing visual comparison to other specimens known to have retractable claws. This was conducted by examining three lines of evidence: the morphology of the middle phalanx module, depth of arc in the claw, and the sizes of the extensor and flexor muscle processes. In specimens capable of claw retraction, the middle phalanx has a curvature on the posterior side, making the bone asymmetrical in shape. Specimens incapable of claw retraction have a middle phalanx that is symmetrical in shape. Retractable claws have deeper arcs in the claw whereas non-retractable claws have a shallower depth of the arc. In addition to this, retractable claws have differing attachment sites of the extensor and flexor processes compared to non-retractable claws. Using this method of visual comparison, it was found that the observed specimen, NDGS 64, was incapable of claw retraction.
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