Titanoceratops ouranos

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Titanoceratops is a remarkable animal. It is known from a single specimen, OMNH (Oklahoma Museum of Natural History) 10165, which was collected from the late Campanian aged Kirtland Formation (~73 MYA) of New Mexico.

The Kirtland preserves lots of specimens of Pentaceratops sternbergi, so when OMNH 10165 was eventually prepared and mounted, it was assumed that's what it was, and reconstructed to look like Pentaceratops. In fact, once the plastered-up bits are removed, there isn't a single diagnostic feature of Pentaceratops in the animal. Instead, the shape of the horns, the snout, and the rest of the skeleton more closely resemble the giant Torosaurus and Triceratops from the late Maastrichtian (65 MYA) of the northern Great Plains.

The original description of this specimen (Lehman, 1998) goes out of its way to list the details in which this animal more closely resembles Triceratops, and they're pretty striking. These include large sinuses invading the horns, the extreme length of the brow horns, the elongate snout, and the deep excavation of the snout by a fossa in the premaxilla. The most striking difference is size: OMNH 10165 is a monstrous animal, with an estimated mass of 6.5 tons. Lehman, using a different equation, gets a mass of 9.9 tons. Either way, this is a very, very big dinosaur- as large as a large individual of Triceratops.

I agree with all of Lehman's interpretations of the anatomy, in fact. He's a good anatomist. I just have a different take on what they mean. Rather than assuming that it represents an extremely unusual Pentaceratops, with a lot of variation in the species, for me the simplest explanation of the extensive resemblance between OMNH 10165 and Triceratops is that it's related to Triceratops, not to Pentaceratops. Phylogenetic analysis bears this out. Whether using a modified version of the Dinosauria matrix or the Sampson et al. matrix, OMNH 10165 consistently clusters with Torosaurus and Triceratops, not Pentaceratops.

This creates a rather bizarre situation: this is a very advanced animal to be occurring so far back in time alongside much more primitive dinosaurs. That raises some questions about stratigraphy- the Kirtland does include some Maastrichtian strata. Attempts to relocate the quarry, unfortunately, were in vain. We can't be entirely certain that the animal isn't from the Maastrichtian, rather than the Campanian. However, the area the specimen is supposed to come from only exposes Campanian rocks. Furthermore, the matrix in which the specimen occurs is classic lower Kirtland and Fruitland Formation in terms of its lithology- its a dark, muddy, organic rich stuff with lots of bits of plant matter and amber. Walking around the coal beds of the lower Kirtland and Fruitland, this is the type of stuff you see.

The idea of Triceratops-like animals in the Campanian hasn't been widely embraced, and I have to admit it strikes me as pretty incredible. I appreciate the fossil record is bad, but I didn't expect it to be quite that bad; there's a huge gap between Titanoceratops and the early Maastrichtian Eotriceratops. But this is what the anatomy tells us, unless Lehman and I are both completely misinterpreting the structure of the skull and skeleton.

Finally, it's worth discussing the issue of ontogenetic variation, i.e. how animals change as they grow. It's recently been proposed that this is a major problem, and that a lot of things we think are separate species are really adults and juveniles. In particular, that Torosaurus is really Triceratops... this isn't the case, however.

You can find the paper here: http://www.sciencedirect.com/science/article/pii/S0195667110001205

Which isn't to say this method is foolproof. A phylogeny is only as good as the characters and the codings. There are some good phylogenies out there, and not so good ones (and obviously I think my phylogenies are among the better ones... but we all think that, and we can't all be right).

I think this also shows the value of doing taxonomy using cladistic methods. The old fashioned "what dinosaur does it most closely resemble" approach is obsolete at this point. Subjective debates about what is/isn't similar enough to belong in the same genus are largely circumvented when you start playing around with phylogenies. Code the specimen, throw it in, and let the computer figure out where it goes. Then you can figure out what species to call it.