Thursday, February 2, 2012

Are Sauropod Skulls Actually Rare?

Hone recently mentioned this old piece of paleontological "common knowledge", but I wonder how true it really is.

For one, we're no longer back in the days of The Dinosauria where only ten skulls could be illustrated by McIntosh.  There have to be a few times that now at least, plus tons known from braincases and/or jaw elements.

Two, just how poorly known are skulls of other dinosaurs?  There are only four or so stegosaur taxa with known skulls, two therizinosaurs, and three alvarezsauroids, for instance.

Three, how much does it reflect the number of sauropods named from axial material as opposed to the percentage of sauropod skulls found per postcranium?  Maybe the elaborate vertebrae of sauropods make them more prone to being named from postcrania, whereas e.g. ornithopod or ceratopsian postcrania are often considered indeterminate.  I suspect if you counted all of the partial cerapod postcrania left undescribed or uncollected, their skulls would seem much more rare.

The first two questions could actually be answered statistically, once my sauropodomorph database were 'complete'.  You would need to try to include only valid taxa (nice and subjective), then find some way to represent cranial completeness (maybe on a scale of 20, where each kind of preserved skull element counts as 1, and having 20 is equivalent to a complete skull), then find the average cranial completeness number for various groups.  The third question would be more difficult, since not only would just trawling museum collections be tedious, it would leave the 'how many aren't collected' part unknown.  And just as I bet there's a bias in not collecting cerapod postcranial bits due to supposed indeterminacy, there's also a bias in not collecting sauropod fossils due to their size.

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