The phylogeny and taxonomy of the Tyrannosauridae Author Holtz, T. R. text 2001 2001-12-31 Indiana University Press Bloomington Editor Tanke D. H. Editor Carpenter K. Mesozoic Vertebrate Life 64 83 book chapter 10.5281/zenodo.3245327 9bf3a9f5-cd36-4be6-bba9-49607815bcd0 3245327 Aublysodontinae is comprised at present of only incompletely known taxa. These forms are united by two dental synapomorphies: 76.I and 77.1 (unserrated premaxillary teeth with prominent vertical ridges on the caudal surface). These derived features are not present on other tyrannosaurids, including the oldest confirmed tyrannosaurid premaxillary tooth (from the Early Cretaceous Jobu Formation of Japan: Manabe 1999 ). Although Molnar and Carpenter (1989) separated Aublysodon from Tyrannosauridae as Family Aublysodontidae , the presence of Aublysodon-llke teeth in specimens of Alectrosaurus olseni , a taxon with tyrannosaurid synapomorphies ( Mader and Bradley 1989 ) led Currie et al . (1990) to include this group as a subfamily within Tyrannosauridae , a nomenclatural practice followed here. Other than the specialized premaxillary teeth, aublysodontines generally retain more primitive coelurosaurian features lost in other tyrannosaurids: for example, the skulls of aublysodontines are longer and lower, the tooth count higher, and the lateral teeth less labiolingually expanded than in derived tyrannosaurines ( Currie in press ). Aublysodon and Alectrosaurus (but not the Kirtland Shale taxon) are smaller than typical tyrannosaurines: however the ontogenetic status of known aublysodontine specimens is hindered by the incompleteness of their fossils, and these might represent juvenile individuals of taxa which reached larger sizes. Aithough Aublysodon is provisionally recognized as a valid name here, Currie et al . (1990) caution that this may not be a taxon, but instead an ontogenetic stage or a sexual dimorph. It might be further added that tooth wear in life, postmortem abrasion, and digestion might also conceivably render a typical tyrannosaurid premaxilla tooth into a nonserrated one. In such a case, the synapomorphies uniting " Aublysodontinae " would be lost, and the remaining resemblances between these taxa would be symplesiomorphies.