Diet and feeding mechanisms are some of the most valuable things we can learn about fossil organisms. In 2010 a crocodile with mammal-like, multicusped teeth and a manoeuvrable jaw was described in Nature (O'Connor et al. 2010). The croc, named Pakasuchus hit the news and was reported in many notable magazines, newspapers and blogs. Pterosaurs, however, have not received such attention. Although later forms lacked teeth (edentulous), or had very uniform dentition (homodont), a large subset of Late Triassic to Early Cretaceous pterosaurs possessed multiple tooth morphologies in their jaws (heterodont). Some tooth morphologies were even multicusped or serrated. Ősi (2011) documented some of this heterodonty, giving a review of feeding-related characters in basal pterosaurs. Ősi's review was comprehensive; however, he did not touch upon the feeding mechanisms of the short tailed, pterodactyloid pterosaurs. This is not surprising; variation in pterodactyloid teeth is usually non-existent in the tooth row itself. Furthermore, the variation between individual species of pterodactyloid usually consists of; short cone to long cone and straight to bent (recurved). In fact, it is nearly impossible to tell the difference between some pterosaur teeth and some very simple croc, plesiosaur or even fish teeth. In some cases careful examination of the tooth structure, or even microstructure must be employed to positively identify a pterosaur tooth (Vidovic, 2010; Vidovic et al. in prep). One particular group of pterodactyloids does break this humdrum cycle though. The ctenochasmatids (Late Jurassic to Early Cretaceous) possess teeth with phenomenal length width ratios; up to 1/75. Gnathosaurus had slender, sinuous teeth which projected horizontally out of the jaw margin, and the smaller Ctenochasma had a similar basket effect with its dentition. Clearly, this particular group of pterodactyloids was sifting sediments in order to filter-feed. By the Early Cretaceous this group of animals had evolved into their role perfectly; Pterodaustro guiñazui, the uncanny cross between a pterosaur, flamingo and whale was certainly filter-feeding directly from the water.
Pterodaustro is one of the most bizarre animals that has ever graced this Earth. It had very elongate forearms and legs, a long neck, big flat feet and its head was longer than its body. Even more bizarre were its jaws, which bowed like those of a whale or flamingo, were slender and elongate like a wading bird, and full of fibrous teeth which are convergent on baleen* (or vice versa). The teeth were so long and slender in fact, a study was conducted to prove, unequivocally, that they were true teeth (Chiappe & Chinsamy 1996). The dentition of the upper jaw is often neglected; it consists of tiny, spatulate, invariable teeth (isodont). As such, Pterodaustro is currently the only pterodactyloid known to have a marked heterodont dentition. So, is Pterodaustro content with being this unusual, well, in a word, NO. Chiappe et al. (2000) reported that the tremendously elongate teeth are not located in sockets, unlike all other pterosaurs, but in an open groove, where the labial ridge (outer side) is lower than the lingual ridge (inside), this is a subthecodont condition. Furthermore, the spatulate teeth of the upper jaw are not in sockets at all. Chiappe et al. (2000) suggested that these teeth and associated bony bits (Yes! Ossicles in the mouth!) were located in a skin integument. I agree with this statement, and I will take it a little further.
* Currey (1999; 2010) noted that the length width ratios of Pterodaustro's teeth were so high that the mechanical properties would allow it to flex a considerable amount without breaking (not necessarily meaning they did).
|Modified from Zweers et al. (1995): flamingo beak in the feeding position, showing the keratinous papillae.|
|a) Reconstruction of Pterodaustro; teeth and ossicles in the upper jaw (b); slender and elongate teeth in the lower jaw; keratinous papillae on the tongues dorsal surface (c).|
All in all Pterodaustro was a pretty freaky flyer, a winged whale, and certainly worth thinking about in more abstract ways. It seems fitting, to both my research and the aims of this blog, for this to have been the first subject of discussion, but there is much more to come.
COMING SOON… more feeding strategies in pterosaurs (a three part series)…
Chiappe, L. M. and Chinsamy A. 1996. Pterodaustro's true teeth. Nature, 379: 211-212
Chiappe, L. M. Kellner, A. W. A. Rivarola, D. Davila, S. and Fox, M. 2000. Cranial morphology of Pterodaustro guinazui (Pterosauria: Pterodactyloidea) from the Lower Cretaceous of Argentina. Contributions in science, 483: 1-19
Codorniú, L. Chiappe, L. M. Arcucci, A. and Ortiz-Suarez, A. 2009. First occurrence of gastroliths in Pterosauria (Early Cretaceous, Argentina). XXIV Jornadas Argentinas de Paleontología de Vertebrados
Currey, J. D. 1999. The design of mineralised hard tissues for their mechanical functions. The Journal of Experimental Biology, 202: 3285-3294
Currey, J. D. 2010. Mechanical properties and adaptations of some less familiar bony tissues. Journal of the Mechanical Behaviour of Biomedical Materials, 3: 357-372
O'Connor, P.M. Sertich, J.W. Stevens, N.J. Roberts, E.M. Gottfried, M.D. Hieronymus, T.L. Jinnah, Z.A. Ridgely, R. Ngasala, S.E. and Temba, J. 2010. The evolution of mammal-like crocodyliforms in the Cretaceous Period of Gondwana. Nature, 466 (7307): 748–751
Ősi, A. 2011. Feeding-related characters in basal pterosaurs: implications for jaw mechanism, dental function and diet. Lethaia, 44: 136–152.
Vidovic, S. U. 2010. A preliminary analysis of dental microstructure in pterosaurs. Acta Geoscientica Sinica, S1
Zweers, G. De Jong, F. Berkhoudt, H. Vanden Berge, J. C. 1995. Filter Feeding in Flamingos (Phoenicopterus ruber). The Condor, 97: 297-324