Fossil Friday – Paramylodon skull


Even if a bone is lucky enough to be preserved as a fossil, time is not always kind. There are numerous ways a bone can be altered after burial, including being smushed by the weight of overlying sediment.

The lump of bone shown above is actually a nearly complete skull of the ground sloth Paramylodon harlani in dorsal view, collected from the El Casco substation in northern Riverside County. It might be a little difficult to interpret because it has been deformed post-burial. Below is an annotated version:


The skull is pushed over so that the midline is displaced to the left. This makes features from the right side like the right eye socket easily visible in dorsal view, while hiding the same features from the left side. The entire skull is also flattened, resulting in the wide foramen magnum at the back of the skull.

Here’s the ventral view:


And the annotated version:


Much of the basicranial part of the skull is a big-ole’ indecipherable mess, but there are a lot of identifiable features, including all of the tooth sockets.

While there are other Paramylodon remains from El Casco, this is the only sloth skull recovered from the site. Even deformed specimens can be significant!

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