Fossil Friday – Paramylodon claw

Sloths are fascinating animals, with all kinds of strange anatomical features. One of their signature characters is their enormous claws. 

Although bones from the ground sloth Paramylodon are relatively common at Diamond Valley Lake, only a few claws were recovered. Technically, what usually preserves is the last finger bone, technically called the terminal phalanx or ungal. This is shown above from the side, and below from above:

While we sometimes refer to ungals informally as “claws”, it’s important to recognize that the ungal is actually the bone that supports the claw. The claw itself is a keratin sheath that fits over the ungal. Keratin is rarely preserved, but there are a few mummified sloths (I don’t think Paramylodon is one of them) in which the keratin claw is preserved; it is generally much longer than the ungal.

Sloth ungals are always crowd pleasers at outreach events, so we recently molded this specimen and have started producing casts. Now that the molds are completed, the original claw will go back on permanent exhibit in the museum.


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