Last week I gave you this specimen from the Dead Zoo’s “Unidentified” drawer:

It’s a big and robust skull, albeit slightly battered, with no teeth and several missing pieces. However, the missing elements didn’t stop Wouter van Gestel and several others from recognising it as being from a sea lion.

That’s a really good start, but there are six living species in the sea lion subfamily (the Otariinae), which is where things get a bit more tricky, especially since they all show a large degree of sexual dimorphism to confuse things. There are also nine species of fur seals, which are close relatives and are also sexually dimorphic and hard to differentiate from sea lions.

However, there was a bit of a clue written on the specimen, for those who looked closely:

So we know that this specimen was collected in 1855 by Dr Kinahan (an Irish geologist) from “Chinchas Is”. This group of three small islands off the coast of Peru is only really known for starting a war between Spain and several South American countries in 1864. It wasn’t actually the Islands that the fighting started over, but the large piles of guano that covered them. But I digress.

The location of the Chincha Islands immediately allows the likely species that this could be from to be narrowed down to two. Of course this is where it gets more complicated – differentiating between the South American Sea Lion and the South American Fur Seal.

However, there is a feature on this specimen which makes it really easy to distinguish from all other sea lions and fur seals, if you know to look for it. First of all, take a look at this very useful paper (pdf) by Sylvia Brunner which gives some great information on the identification of the various species.

Then, take a look at the palate of the specimen. Notice that the palate ends in a line with the point where the rear portion of the zygomatic arch meets the skull (see the red line in the image below if that doesn’t make sense):

In every other species of fur seal and sea lion the palate ends at around the midway point of the zygomatic arch (where the writing ends on this specimen). There is just one species with such a long palate, the South American Sea Lion Otaria flavescens (Shaw, 1800) which is also referred to as O. bryonia.

It’s rare to find such a clear-cut indicative feature on a skull, so it’s always satisfying when you find one. I should note that this skull is from a female. The males are much more massive, but still share that feature of the palate.

So particular congratulations to Rémi and katedmonson who got the genus Otaria. Next time you have a sea lion skull to identify (as I’m sure you will) make sure you keep in mind that handy feature as the first thing to check and if that doesn’t help the be sure to check our Brunner’s paper.