Photo of the Day #892: Manatee skeletons


The skeletons of an adult and a juvenile manatee (Trichechus manatus), on display at the North Carolina Museum of Natural Sciences.

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The ribs are pachyosteosclerotic - i.e. pachyostotic (ribs inflated outwards with dense bone) and osteosclerotic (medullary cavity smaller, rimmed by dense bone). This is an adaptation for negative bouyancy - otherwise, they'd have a hard time staying submerged. Sirenian bones are extremely dense, to the point where sometimes fragments of their bones in the field can be mistaken for fragments of teeth.

There's a dugong skull in the local natural history museum, so I'm unfazed by the bizarre appearance of the manatee skull. It's the body that freaks me out- pachyostotic ribs, and check out the fingers! If all sirenians were extinct, I wonder if there are any clues that would prevent us from restoring them with webbed hands instead of flippers.