A few weeks ago, I posted this image:
And I asked this question:
“One of these is NOT a theropod dinosaur. Can you guess which is which?”
After a few weeks, I’m closing this gripping debate:
A is Goyocephale lattimorei, an ornithischian. Expect similar morphology from Heterodontosaurus tucki. More specifically, they correspond to the first premaxillary “fang,” which I discuss here.
B is a generic troodontid.
C is Richardoestesia gilmorei. The rectangular, closely-spaced denticles are a dead giveaway, although they occassionally come with hooks (like in A).
D and E are both therizinosauroids. D represents a morphology known for derived “therizinosaurid” forms like Erlikosaurus andrewsi, Segnosaurus galbinensis, and Nothronychus mckinleyi. E is Alxasaurus elesitaiensis.
So what’s F? F is odd; while you might expect the common form of theropod — especially highly predaceous theropod — teeth to have hooked denticles, slightly hooked and certainly perpendicular (rather than apically inclined, as in all of the others shown here except C). F, of all things, is from a tooth referred to Saurornitholestes langstoni. It’s Judithian, from the US, and the morphology of the crown is very Saurornitholestes-ish. But that’s a subject I can get into elsewhere, and have already touched on on this blog.
None of these teeth, with the exception of C, which is diagnostic of “richardcoestesian” teeth but also found in some tyrannosauroids, are immediately discernible from the others. Some, perhaps due to the quality of the art produced (my fault), show that mere shape of the denticles, hooking, the quality of the sellae between teeth, the extent of the sulci that pass from the sellae onto the crown surface, their inclination, the degree of “hooking,” etc. If these features are diagnostic, they are hardly used (by any specific quality) to discriminate teeth. One alternate, more conservative approach, is to be less judgmental on their morphology, that they can vary crown to crown in a single dental series. This is less well-known, but demonstrable in some dentitions. We’ll get to that eventually on this blog.