I went on the Audubon Christmas Bird Count a couple of weeks ago, and while we didn’t have any stand-out birds to report, it was a banner day for bones and skulls. The day’s discoveries included a murre skull, an eagle skull, a partial sea lion skull, a moose jaw, and numerous bird and mammal bones.
Plus this sea otter skull. Sea otters are increasing dramatically in Southeast Alaska. Fifteen years ago it would have been a shock to find a sea otter skull; I’ve seen at least three on or near the local beaches just this year.
Sea otter skulls are similar to river otter skulls, but there are some key differences. The average sea otter skull is visibly bigger than the average river otter skull, with a bigger nasal opening (I wonder why?) But even without these differences, the teeth distinguish them easily. Eaters of hard-shelled prey such as clams and crabs, sea otters have flattened, smooth-cusped molars where river otters have tendon-shearing carnassials.
This otter was probably several years old, judging from the skull size and the worn condition of its molars. I think the canine tooth was broken post-mortem; the break was sharp-edged and splintery, not worn at all.
Sea otters spend a huge amount of time grooming their fur, which is their primary insulation (they don’t have blubber). Looking at those precisely-shaped, comb-like incisors makes me wonder if their shapes have any special adaptive functions for fur maintenance…