Allometric growth in tyrannosaurids (Dinosauria: Theropoda) from the Upper Cretaceous of North America and Asia

Many tyrannosaurid skeletons have been collected in Canada, the United States, and Mongolia. These fossils tend to represent mature individuals, but juveniles are also known. Skeletons of five genera of tyrannosaurids representing two distinct clades (albertosaurines and tyrannosaurines) were measured, and bivariate analysis was done on 85 dimensions. Allometric differences among mature specimens of different species are shown to be trivial when compared with the allometric differences associated with growth. Nevertheless, albertosaurines tend to be more lightly built than tyrannosaurines. When compared with a tyrannosaurine of the same absolute size, albertosaurines had slightly shorter, lower skulls, shorter ilia, longer tibiae, longer metatarsals, and longer toes. The arms of albertosaurines and tyrannosaurines are the same size, with the exception of Tarbosaurus, which has shorter front limb elements. Tooth counts show individual and interspecific variation, but there is no evidence that tooth numbers are controlled by the size or age of an animal. Dinotyrannus, Jenghizkhan, Maleevosaurus, Shanshanosaurus, Stygivenator, and possibly Nanotyrannus have proportions that suggest they are ontogenetic stages of either Tarbosaurus or Tyrannosaurus.