Observations on Paleospecies Determination, With Additional Data on Tyrannosaurus Including Its Highly Divergent Species Specific Supraorbital Display Ornaments That Give T. rex a New and Unique Life Appearance

Abstract

Intrageneric dinosaur species have been being named for decades without either significant examination of the methods and standards used to do so, or widely publicized controversy over the results. The long standing assumption that all large known specimens of the iconic North American Tyrannosaurus consisted of just the one popular species T. rex was recently challenged with the first comprehensive test of the question. The result was the diagnosing and naming of two additional taxa, T. imperator and T. regina, based on a number of species levels characters regarding robustness and tooth proportions in the context of their stratigraphic distribution. In association a rare in-depth look was taken at the current state of naming vertebrate paleospecies, which it turns out are not highly rigorous because of inherent problems with the species concept and other matters. The results of the paper were severely criticized in in a manner never seen before for new dinosaur species even when based on less evidence. This study takes another look as the determination of paleospecies, and shows that many of the claims made in the criticisms regarding the Tyrannosaurus species work were inaccurate. New data on the proportions of strength bars in Tyrannosaurus skulls reinforces the basing of the three species in part on robustness factors, and allows all but one skull to be assigned to one of the species. These results allow the first detailed systematic examination of the supraorbital display bosses of the genus. They sort out as visually distinctive species specific ornaments based on both stratigraphic and taxonomic factors, strongly affirm that Tyrannosaurus was multispecific, and the species probably dimorphic. New skulls of T. rex show that the species sported, males probably, striking display bosses not yet observed in other tyrannosaurids.