Sunday, July 19, 2009

New skull!

Hey everyone,

Here is probably what will constitute the find of the summer. This is a partial skull. But, I'm not going to say what it is. A couple of you might have an idea, but I want real ID's based on cranial anatomy.

Good luck!


Brian Lee Beatty said...

If it is laying with its ventral side up and heavily eroded, I would think it is an odontocete of some sort. Even though the shape of it is superficially like a crocodylian, the occipital condyles are clearly mammalian. The shape looks like what you would see if the erosion had cut through the skull at a plane slightly oblique to horizontal, with the plane rising to the dorsal side as one goes more rostral. That might explain why at the bottom of the picture it looks like a section near the base of a skull, and at the front it looks like a section closer to the dorsal side of the more proximal portion of the rostrum.
I could be totally wrong, but if not, and assuming it is complete below the erosion, you would have most of the important portions to identifying what sort of odontocete it is. The vertex should be there, as well as some of the base of the skull. I wonder if the bulge sitting in the matrix-filled cavity in the lower left portion of the picture is an auditory bulla?
What do you think?

Brian Lee Beatty said...

or could this be just a funny cut through a desmatophocine skull?

Anonymous said...

Oh, pick me! I know!

Robert Boessenecker said...

Hey Brian,

I can definitely see the resemblance to the ventral side of an odontocete skull. I intentionally left out a scale bar to make this more confusing (and given the fact that noone attempted this for a couple weeks tells me I should have included it).

What I assume you're identifying as the basioccipital is actually the supraoccipital. Additionally, the whole slab is about 2 feet wide. While not obvious from the photo, the top of the specimen is pyramidal in shape. The cranial vertex is worn away, but nonetheless the top of the skull is there.

The triangular and anteriorly thrusted supraoccipital shield identifies this as a mysticete (granted, there are some early odontocetes with this feature, i.e. Simocetus; these are typically Oligocene in age, and this specimen is early Pliocene).

In any event, the narrow dorsal ridge on the left squamosal (the only part exposed), the very narrow supraoccipital, and an exoccipital that projects posterior to the occipital condyles are all features that identify this as Herpetocetus (these may all be apomorphies, but I can't recall 100%).

So, go figure - I like Herpetocetus, and I'm predictable - but it is definitely a very strange little mysticete.

Robert Boessenecker said...

P.S. see the following picture for comparison:

I'll post a better follow up to this once I'm off vacation.