Premaxillary teeth with D-shaped contour are present in tyrannosaurids (Brochu, 2002; Choinere et al., 2012) and megaraptorans (Porfiri et al., 2014), but are they the only theropod dinosaurs to have these teeth? Thanks in advance for your opinion
It depends on what you mean by "D"-shaped. Tyrannosauroids uniquely have a U-shaped cross-section where both carinae are equally distally (lingually) placed. Many other averaptorans (including abelisaurids and allosauroids) have asymmetrical premaxillae that might arguably be called D-shaped, but they do not conform to the tyrannosauroid condition. Megaraptorans are intermediate between tyrannosauroids and allosauroids in this configuration.
Thomas: many thanks for your useful response. In this way, I guess it would be great to use quantitative parameters that might reflect graphically these qualitative differences in the configuration of the premaxillary teeth.
I actually recently investigated the distribution of U-shaped, D-shaped, J-shaped, and what I call 'salinon-shaped' cross sections at the cervix in mesialmost crowns in non-avian theropods. This paper is currently in review and will hopefully be published next year. I proposed to differentiate U-shaped, D-shaped, and J-shaped cross-section outlines in my paper on abelisaurid teeth from Portugal, so that the D-shaped cannot be used to gather mesialmost teeth with carinae entirely facing lingually (what I referred to a U-shaped outline) from those with a mesial carina and a distal carinae facing linguo-mesially and linguo-distally, respectively. Dr. Holtz is right by saying that the U-shaped condition is only shared by some Tyrannosauroidea (i.e., Eotyrannus, Dilong, Guanlong, Xiongguanlong, tyrannosaurids), although it seems that this condition also occurs in the basal coelurosaur Zuolong salleri (Choiniere et al., 2010). A D-shaped cross-section characterizes Allosaurus mesialmost teeth, and sinraptorids and possibly neovenatorids (if you consider megaraptorans to be allosauroids) have a D-shaped and/or J-shaped cross-section (a crown with a J-shaped cross-section outline is characterized by a twisted mesial carina and a concave surface adjacent to the mesial carina on the lingual side of the crown). A J-shaped cross-section is also seen in dromaeosaurids such as Dromaeosaurus. It also occurs in abelisaurids but in teeth making the transition between the mesialmost and lateral dentitions. The mesialmost abelisaurid crowns (first dentary and premaxillary teeth) are salinon-shaped in outline, i.e., they have a concave surface adjacent to both mesial and distal carinae, on the lingual surface of the crown, making the cross-section a flying-saucer shape outline. The mesialmost teeth of non-averostran theropods and megalosauroids are relatively symmetrical and oval or lenticular in outline. This is also the case in carcharodontosaurids such as Acrocanthosaurus, in which the mesial carina is facing mesiolabially (like megalosaurids and some ceratosaurids), giving a lenticular or lanceolate outline of mesialmost crowns. Some basal tyrannosauroids such as Proceratosaurus show a J-shaped cross-section, and some allosaurid mesialmost crowns also display a salinon-shaped cross-section outline. Ornitholestes seems to have both D-shaped and J-shaped crowns, and noasaurids like Masiakasaurus have the salinon-shaped cross-section outline shared with other abelisauroids.
Thanks Christopher, really this is a very complete answer, showing that you have reviewed many specimens and sure your next paper is very interesting, thanks for the information ahead
Very welcome! Feel free to contact me regarding theropod teeth if needed!
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