ENAMEL MICROSTRUCTURE OF THEROPOD TEETH: A CHARACTERIZATION OF SPECIMENS FROM THE CRETACEOUS OF PATAGONIA

FEDERICO A. GIANECHINI; DIEGO POL; EMMA C. VIEYTES

San Juan

Congreso; IV Congreso Latinoamericano de Paleontología de Vertebrados; 2011

Enamel is the mineralized tissue that covers the amniote teeth, whose microstructure is constituted by apatite microcrystals arranged in a particular order (Sander, 1999; Stokosa, 2005). In mammals, these microcrystals are organized in such a way that they form prism-like structures (Sander, 1999). The mammalian enamel can be easily observed under polarized light. Conversely, the enamel of reptiles (including dinosaurs) is not prismatic, and therefore can only be observed through scanning electron microscope (SEM) (Sander, 1999, 2000; Hwang, 2005; Stokosa, 2005). Observations on theropod enamel have been mainly performed for Laurasian taxa (e.g., Tyrannosaurus, Velociraptor, Troodon, Sander, 1999; Stokosa, 2005) and only a few Gondwanan taxa (e.g., Carcharodontosaurus, Spinosaurus, Buffetaut et al., 1986). Recent research has revealed that, despite the convergence observed in the microstructure of theropod enamel, many monophyletic groups have characteristic types of enamel and, therefore, enamel microstructure can be phylogenetically informative, at least at the family level (Hwang, 2005). A characterization of isolated teeth from the Cerro Barcino Formation (Aptan-Albian?) of Chubut Province, that have morphological similarities with abelisaurid, carcharodontosaurid, and dromaeosaurid teeth, is here presented, complementing previous studies on Gondwanan taxa. Additionally, the enamel microstructure of Tyrannotitan chubutensis Novas, De Valais, Vickers-Rich and Rich, 2005 is also presented here. In isolated teeth that morphologically resemble either abelisaurid or carcharodontosaurid teeth, the microcrystals are arranged in columns in the basal half of the enamel and in a parallel arrangement along the outer half, with incremental lines, as the enamel microstructure of tyrannosaurid and carcharodontosaurid teeth. The enamel of isolated teeth morphologically similar to dromaeosaurid teeth is mainly constituted by parallel crystals, in some cases also showing incremental lines, as the microstructure of troodontids and dromaeosaurids. The enamel of Tyrannotitan is columnar, as in Carcharodontosaurus, but in contrast to the latter, incremental lines predominate in the basal half. Thus, studies based on enamel microstructure are important not only to complement studies of theropod teeth, but also to identify the phylogenetic affinities of isolated theropod teeth found in Cretaceous units of Gondwana.