Geobulletin alpha

Source info:

Author:	Emile
Date:	2008-09-08 09:47:00
Blog:	The World We Don't Live In
URL:	http://eobasileus.blogspot.com/2008/09/of-polyglyphanodonts-and-their-teeth.html

Summary:

Most lizards aren’t particularly good chewers. Usually, food processing tends to be of the “swallow it whole” variety, with some chomping if prey proves resilient. Nevertheless, at least some lizards had a reasonable chewing apparatus, as evidenced by the latest data on the extinct polyglyphanodonts, or transversely-toothed lizards.The Polyglyphanodontinae was a Maastrichtian clade of lizards, with fossils known from Asia and North America. The best-known polyglyphanodont (and the general subject of this discussion) is Polyglyphanodon sternbergi Gilmore, 1940. These were probably stout, herbivorous lizards; an illustration in Dixon (2008) shows something like a heavyset skink. If they were lucky, they looked something like the teiid in the photo above (taken from Wikipedia).A recent study (Nydam and Cifelli, 2005) examined the unusual teeth of Polyglyphanodon. The teeth, described by Gilmore (1942) as being “smooth” and “sharp-edged”, were found to be crowned with minute, asymmetrical serrations. Furthermore, the teeth are transversely-oriented, get larger in the back of the mouth, and interlock neatly with each other, as shown in the diagram (from Nydam and Cifelli (2005)).Given that polyglyphanodonts were probably herbivorous (as initially suggested by Gilmore, 1942), then the teeth were involved in food processing of some sort. While the serrations bear comparison with those on the teeth of Iguana, the resemblance is superficial. Iguanas crop vegetation with scissors-like teeth at the front of the mouth, while Polyglyphanodon could have sliced food with its entire tooth row (Nydam and Cifelli, 2005). Furthermore, the occluding teeth could have cut up food, which may have lead to improved digestion – as opposed to the iguanas, which swallow bites of food whole. Nevertheless, the teeth do not show signs of wear, and it would seem that food processing was minimal (Nydam and Cifelli, 2005). At best, Polyglyphanodon and its herbivorous relatives merely mashed food up a little before sending it to the stomach, as opposed to thoroughly chewing it.Apart from Polyglyphanodon, a similar dental arrangement is known in the polyglyphanodontine Peneteius aquilonius. This smaller lizard had decidedly mammal-like multicuspid teeth, which probably helped in butchering arthropods (Nydam et al., 2000).Polyglyphanodonts are generally assigned to the scincomorphans, and were probably closely related to the teiids of today. A phylogenetic study by Nydam et al. (2007) defined a monophyletic Borioteiioidea, which included the American and Asian polyglyphanodonts and was the sister clade to the Teiioidea (including Teiidae and Gymnophthalmidae). Adjacent cladogram is from Nydam et al. (2007).Don’t bother searching for polyglyphanodonts in popular books, though. The only one I ever found was in Dixon’s massive 2008 encyclopedia of prehistoric life, which I reviewed previously on this blog.ReferencesDixon, D. (2008) The World Encyclopedia of Dinosaurs and Prehistoric Creatures. Lorenz BooksGilmore, C.W. (1940) New fossil lizards from the Upper Cretaceous of Utah.Smithsonian Miscellaneous Collections 99: 1–3Gilmore, C.W. (1942) Osteology of Polyglyphanodon, an Upper Cretaceous Lizard from Utah. Proceedings of the United States National Museum 92: 229: 265Nydam, R.L. and Cifelli, R.L. (2005) New data on the dentition of the scincomorphan lizard Polyglyphanodon sternbergi. Acta Palaeontologica Polonica 50 (1): 73–78Nydam, R. L.; Eaton, J. G.; and Sankey, J. (2007) New taxa of transversely-toothed lizards (Squamata: Scincomorpha) and new information on the evolutionary origin of “teiids”. J. Paleont., 81(3), 2007, pp. 538–549Nydam, R. L.; Gauthier, J.A.; and Chiment, J.J. (2000) The mammal−like teeth of the Late Cretaceous lizard Peneteius aquilonius Estes 1969 (Squamata, Teiidae). Journal of Vertebrate Paleontology 20: 628–631

Content analysis:

Stratigraphic context:

Recognized stratigraphic terms [n]:	Maastrichtian [1]
Agenames chronostratigraphy [rating]:	Maastrichtian [0.1] Upper Cretaceous [0.1] Cretaceous [0.1] Mesozoic [0.1] Phanerozoic [0.1]