Convergent Skulls: Walrus and Elephant

I was watching on episode of Oddities a while ago (a great tv series for skelephiles and other fans of odd stuff), and someone brought in a walrus mandible (actually both mandibles fused). The expert they had look at the bone commented on how similar it was to an elephant mandible, despite the very different diets of the two animals.

That got me thinking about walrus and elephant skulls and the similarities they have evolved, largely due to the fact that both animals need skulls that can support a massive pair of tusks. Of course, there are also a lot of differences, but have a look at these simplified illustrations.

Obviously, these are not to scale. I don't have anything profound to say here, just that it's cool to think about how the bones of animals can be so similar or so different, depending on how they developed.