Fossil Friday – juvenile mastodon humerus

11-13-15b

It’s been over two months since we’ve featured a mastodon for Fossil Friday, which seems a little odd for the Valley of the Mastodons, so this week we have a mastodon humerus.

This is a left humerus (the upper arm bone), seen above in approximately anterior view. The proximal end (closest to the shoulder) is on the left, while the distal end (closest to the elbow) is on the right. Below is the same bone in posterior view:

11-13-15a

The ends of the bone are indistinct and have no obvious articulations with other bones. While there is some damage to the bone, the primary reason for this is that this was a very young mastodon. The humerus starts out as three different bony components, a main shaft and epiphyses at each end that are all held together by cartilage. As the animal grows the elements eventually fuse together into a single unit, but if the animal dies before it’s fully grown the epiphyses may fall off as the cartilage decays. That’s what’s happened in this case, with both the missing epiphyses and the small size indicating that this was a very young mastodon.

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