Last week I gave you this nice robust skull to have a go at identifying:

It proved a little bit more of a challenge than I originally expected, at least in terms of getting a species level identification.

So despite a somewhat ursine (bear-like) overall appearance, that may have confused a few people at first, this has all the features you’d expect to see in a male sea lion. In that it’s big, craggy, has huge open sinuses opening into the orbital region (nobody wants their eyes to be overly pressurised when they’re diving) and the teeth are relatively undifferentiated in the back part of the mouth, but they’re well adapted for fighting up front.

However, it turns out that there aren’t a huge number of resources online to see and compare the skulls of these beasties (and the ones that do exist aren’t necessarily the easiest to navigate). So while almost everyone figured out the sea lion bit, the species choice went a bit off track.

Most people plumped for the Steller’s Sea Lion, which (it must be admitted) looks very similar. But this is actually the skull of a Southern Sea Lion Otaria flavescens (Shaw, 1800).

I talked about this species before on Zygoma (many years ago now), with a specimen from the Horniman Museum, where I provided some links to the Marine Species Identification Portal. Sadly, that resource has been retired, but fortunately Naturalis Biodiversity Centre rescued the content and has kept it available online. It provides drawings of the skulls of both Steller’s and Southern Sea Lions and if you take a look at few key features you’ll spot the differences.

One major indication is the length and shape of the palate. The Southern Sea Lion has a very long palate, which terminates almost in line with the mandibular articulation, whereas the Steller’s terminates further forward. There are a few other features, but that one is the most immediately obvious.

So, a hearty congratulations to a variety of folks on Twitter who spotted that this was the Southern Sea Lion, but there’s no shame in not getting the correct species if you picked Steller’s, given how few resources there are that allow a really good comparison. I hope you enjoyed the challenge!