Today we have Taissa Rodrigues discussing her work on the taxonomy of Brazilian pterosaurs.
First of all, I’d like to thank Dave for his invitation. I have been studying a group of mostly Brazilian pterosaurs, the Anhangueridae (Dave’s comment: part of the ornithocheiroids as recently pictured here with more on pterosaurian taxonomy here), for almost three years now – together with my advisor, Alex Kellner, who in turn described the anhanguerids for the first time together with his advisor. Unfortunately, my thesis topic can be kind of boring for anyone who’s not THAT interested in anhanguerid taxonomy, so on this post I will do my best to tell something a little less restricted.
Overall, Brazilian toothed pterosaurs all looked pretty similar to each other. They had long snouts with sharp teeth, and most probably fed on fishes. They lived on the Araripe Plateau, which 120 million years ago had a very large lake, with an increasingly larger connection to the ocean as time passed by. The Araripe pterosaurs, especially those from the Romualdo Member (or, depending on the author, the Santana Formation), show a remarkable preservation. This enabled some researchers to make inferences on their flight, terrestrial walking, etc. It is then at least curious to think that we know so little about their taxonomy and systematics – in other words, what is an anhanguerid? How are anhanguerid species related to one another? And what about the other toothed pterosaurs from the same deposit?
The Anhangueridae has been largely diagnosed on the base of an anterior expansion of the skull and mandible, which beared the large grasping teeth, and also by the presence of a sagittal crest on the anterior portion of the skull and mandible. Other toothed pterosaurs from the same deposit show the large teeth and the corresponding expansion, but did not have crests. More: there is a group of mostly English pterosaurs, the ornithocheirids, which have been pointed out as similar to the anhanguerids. Some of them show anterior expansions and crests; some only the expansions; some only the crests; and some neither! So the big question here is: do all those species really relate to one another, and if yes, how?
There is much speculation on the function of those crests, and they influence directly the taxonomy of the group. If the crests grew during ontogeny, then crestless animals should be juveniles of crested specimens. However, there are some specimens that do not corroborate this hypothesis: we know of juveniles that already have crests.
If only the males have crests, then the crestless specimens would be females. However, it seems that among living horned mammals, even the females show them, yet smaller. Still, I know only two specimens of Anhanguera that have both the skull and hip preserved. That’s unfortunately not enough to make assumptions on gender, and perhaps future discoveries will help on this subject. The option we adopt is that the presence of crests is a diagnostic feature, i.e., it is taxonomically informative and can be used to differentiate groups of pterosaurs.
Now that you have an overview of the problem, I can describe a little bit of the subject of my paper: a review of the genus Coloborhynchus. It was first described in 1874 by the famous British paleontologist Richard Owen (he’s the one who coined the term Dinosauria, by the way) upon a very fragmentary piece of the rostrum from England. Also, it was once considered a synonym of another genus, Ornithocheirus (another rather problematic taxon), but it was reviewed in 1994 and now there is a consensus that they are distinct from each other (probably the only consensus regarding Coloborhynchus). Since this revision, a taxonomic debate has started, with several species from the Brazilian genus Anhanguera being referred to the genus. This subject extends beyond the taxonomic issue itself, having also biogeographic implications.
Each person who has studied the genus has described new features that enabled us to compare them with other specimens, including undescribed material, and review the genus. It is interesting to note how science works here: the evidence (the fossils) is the same, yet different views have arisen. In our case, we went after what we believe is a conservative view, requiring fewer assumptions.
In such a relatively small fragment, which is the case of the holotype of Coloborhynchus clavirostris, it is possible to observe so many differences from the other species referred to Coloborhynchus that we have placed it as a separate genus. An American species, originally described in Coloborhynchus, was relocated to a new genus. We also made an effort in proposing diagnoses based only in unambiguous characters. Our current view differs from previous ones mostly on the interpretation: what others have seen as evidence of a close relationship, we believe can be primary apomorphies for more inclusive groups, or even convergences, as several features appear in different species of the Anhangueridae and Ornithocheiridae.
As to the Brazilian and British species… well, there’s still a lot of research going on to try to clarify their phylogenetic affinities. We have run some very preliminary analyses and so far the results are rather ambiguous. The Anhangueridae and the Ornithocheiridae seem to be a monophyletic group, but… well, enough to say by now that there is still much work to do.