Sunday, November 8, 2009

Reconstructing a fossil walrus, part 2: the finished product

So, quick rehash of part 1, in case you're really that lazy. To reconstruct the cranium and jaws of Dusignathus santacruzensis (which has an 'exploded' holotype cranium with isolated parts that don't quite match up well), I used more complete material of a younger species, Dusignathus seftoni, from the late Pliocene San Diego Formation. I used the skull of D. seftoni as a template to 'hang' the various parts of D. santacruzensis on to.
Cranial mosaic of Dusignathus seftoni with holotypic fragments of Dusignathus santacruzensis 'hung on'.

From here, it was pretty much an exercise in printing it off, tracing it, and inking it out (followed of course by scanning and some image editing). Below is the finished product.

New cranial restoration of Dusignathus santacruzensis.

Cranial restoration of Mitchell (1975).

Compare this with the older cranial restoration of Dusignathus santacruzensis by Mitchell (1975); there are some obvious differences, including a significantly smaller orbit, and a dorsoventrally shallower cranium, which serves to make the dentary appear much more massive.

Cranial reconstruction of Dusignathus santacruzensis with photos of crania
Dusignathus seftoni and Gomphotaria pugnax. Not to scale.

So... that's basically that. During my lifetime, I want to test this hypothesis of what this animal looked like by finding a new cranium of D. santacruzensis; this won't be easy, and will probably take a lot more searching (i.e. decades). Wishful thinking, I know... Otherwise, I hope that this gives you folks some ideas on how to tackle similar problems with incomplete material you may be studying.

Mitchell, E.D., jr. 1975. Parallelism and convergence in the evolution of the otariidae and phocidae. In Biology of the Seal, p. 12-26.


Doug said...

Thanks for that. It's a nice little example of how fossil reconstruction works. Interesting how the teeth, not just the canines, protrude forward. Or is that standard for pinnipeds?

Well if you ever need a second pair of eyes looking for that walrus skull, I'd be willing to volunteer.

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Robert Boessenecker said...

Thanks for the comments! Sounds like my engagement ring-hungry girlfriend is trolling me...

Doug: "Most" pinnipeds have vertically oriented postcanines; some have the postcanines radially oriented in an arc - anteriors face anteriorly, translating to posterior towards the M1. Pinnipeds that do that are some otariids, and some fossil odobenids such as Dusignathus (I haven't seen as many phocid dentaries, so I can't tell you there).