Geometric and linear morphometric approaches to establish taxonomic identity of a controversial tyrannosaurid maxilla specimen

An isolated maxilla of a tyrannosaurid theropod was reported from the Javelina Formation (Maastrichtian) of the Tornillo Group of Texas several decades ago. Since then, the taxonomic identity of the specimen has remained controversial: some regard it as a specimen of Tyrannosaurus rex, a common tyrannosauroid species in the late Maastrichtian of western North America, while others have raised a possibility that it might represent a distinct taxon, based on the small size, and proportions of the anterior body, maxillary fenestra and jugal ramus. In this work, the taxonomic identity of this controversial specimen is reassessed, using linear and geometric morphometric analyses. Both analyses find the Javelina maxilla specimen is indistinguishable from the hypodigm of Tyrannosaurus rex. Furthermore, results of the geometric analysis suggest the supposed unique morphology of the specimen may not be attributable to allometry or ontogeny, but may simply fall within the range of intraspecific variation. Thus, there seems to be no clear evidence that this specimen is distinct from Tyrannosaurus rex, and the hypothesis that a tyrannosaurid taxon from the Javelina Formation represents a different taxon, is tentatively rejected.