The Brush Narrow and Broad

Typically, I would be hesitant to use this material for any purpose, as it not only represents an undescribed specimen, but is also a cast. I cannot verify its authenticity.

Cast of a skull of an oviraptorid (which I provisionally call "Mitrata"), from Witmer Lab's online collection. Note both the "mitrate" striated premaxillo-nasal crest and the scleral ossicles, which form a complete ring. The scale bar to the right is in centimeters.

I discussed the issue of this specimen with Robert Gaston years ago, who owns the company that made this and provided the material to Witmer’s Lab, and feel that while this specimen actually exists (I’ve seen photos of the original, or what I think are the real thing), the varifiability of material that exists in private hands is difficult. It’s a dangerous path to tread. If I slipped too far on one side, I might go over, and validate in the most extreme case any specimen I might have a photo of. But on the other hand, there is a useful value to a superficial feature involved when the data is available to the public in general. This specimen is prominently featured at Witmer’s Lab (although it goes by the unfortunate header of Oviraptor philoceratops, which is most certainly incorrect), and secondary — and tertiary — verification of the specimen’s existence and nature allow me to think the photos do the material justice. I just can’t prove that to you, and that’s where sticking to the “light side” of verifiability gets me.

I care about this material for various reasons, largely because it may represent new taxonomy and also because it clarifies new things otherwise unknown in oviraptorids (like the scleral ring). But the value of this in context requires workers to examine the original, and have anyone who would wish to verify or refute that work to do the same. They cannot when that material is in private hands. If it were privately owned, but in a public repository (as happens on occasion in various museums) this would be better, as this allows access and thus verifiability and the chance at new and further study. But this is not the case. It is questionable then, when new material that is useful for Science, that any author publishes or publicizes it in a way that allows few to no other people to verify the results of any analysis, such as the publication on two nyctosaurid pterosaur specimens (KJ1 and KJ2) by Chris Bennett (Bennett, 2003). What are we to do when someone does manage to use this information, which informs their work, but we cannot step up and use the same specimens to reject or validate it when further data presents itself? Based on the large volume of material I’ve seen or have had photos in my hands of that are now private or undescribed, I could say a great many things, but do not out of professional courtesy. This is not a rejection then of Bennett’s desire to publish on something that could be lost to Science, lest it never be known, but because if it is lost, we can never realistically say much of what could be a critical specimen. What if we’d lost the type specimen of Sinosauropteryx prima to a private collector? We’d never have had the re-ignition of the feathered-dinosaurs debate, for one thing, and we may have precipitated losing more [critically important] material from the Liaoning lagerstätten simply because of this.

I want to see this specimen in person, and I want to know what it is and what it can inform me. It should be fully prepared, and measured to within a milimeter of its life. It should be … but it may never be. And that’s a shame, because it could tell me I’m wrong. I wrote not that long ago about the subject of giant eyeballs in oviraptorids (here), a projection I based on the shape and circularity of the orbit. This is a good proxy in several animals (mammals, ichthyosaurs, etc.) but less so in reptiles. A specimen does exist to refute my argument, but it’s a cast of a privately-held specimen, which I mentioned here in passing. In fact, it’s that one right up there.

Skull of a PIN oviraptorid skull (provisionally, "Big Beak"), as above, but with a green "eyeball" inserted into the orbits. Because of the point of section where the rostral view of the skull is shown, the "eyeball" appears to overlap limiting bones -- this is an illusion.

Here we have my illustration of the skull of “Big Beak” in three views, showing two different potential sizes of the eyeball in nested green circles. I argued that the shape of the orbit would imply that the eyeball may have filled it almost entirely, as it does in, say, ichthyosaurs.

The first Temnodontosaurus platyodon skull, as found by Mary Anning. Stolen from Wikipedia.

Strong circularity of the orbit seems like a useful proxy for inferring scleral or eyeball size, save when you get to silly things like the skull at top, where the scleral ring is barely 50% of the orbit. What gives?

So on the face of things, I seem a tad wrong (understating this, of course). My projection was that the strong circularity was a good indicator or size of the eyeball, but it is not actually relevant. While this is true for some taxa, it may not be true for many terrestrial vertebrates. Similarly, body scaling has an influence on eyeball size, such that larger animals have larger eyeballs. But the PIN skull above (“Big Beak”) is a very small animal, with a skull length around 4 in (10.3 cm), while “Mitrata” skull up top is a little over 7 in (18.2 cm); the orbit of” Big Beak” is just about 1 in (3.25 cm) and represents 31% of the skull length, while that of “Mitrata” is 29% of skull length, so there is a slight different in orbit size, though it is not substantive. This ratio is pretty characteristic of oviraptorids, rather, with the likely exclusion of Oviraptor philoceratops itself (oddly).

So maybe their eyeballs weren’t so bleedin’ enormous after all, and the image below is a more correct representation of the eyeball size (still pretty big, though).

Skull of a PIN oviraptorid skull (provisionally, "Big Beak"), as above. The third, smallest green circle in the orbit is the newer projected maximum eyeball diameter, matching the maximum diameter of the sclerotic ring.

At this point, though, this raises more questions about what was being used in this enormous about of orbit space to both enforce circularity as well as increase the relative size of the orbit to the skull. This makes me wonder if the scleral ring, rather than the orbit, stays static while skull size increases, such that “Big Beak” would have the same size eye as “Mitrata” up there, but at much smaller head size.

And the thing is, I won’t know I know I’m wrong unless I can show that scleral ring is really there. I need more specimens, better data, and more available verification than photos of specimens in whose hands I cannot study.

Bennett, S. C. 2003. New crested specimens of the Late Cretaceous pterosaur Nyctosaurus. Paläontologische Zeitschrift 77:61-75.

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