Paper No. 118-8
Presentation Time: 3:30 PM
HYPOTHETICAL DIVERGENT EVOLUTION OF TWO APEX PREDATORS FROM THE HELL CREEK FORMATION: NANOTYRANNUS LANCENSIS AND TYRANNOSAURUS REX
The identity of Nanotyrannus has been the subject of great debate for paleontologists for years. After examining the remains of juvenile specimens of closely related tyrannosaurs such as Tarbosaurus bataar, we have seen that the ontogeny of species that are closely related to Tyrannosaurus rex are not as drastic as the ontogeny model of T.rex proposed by Carr et al. Horner et al. also claims that the tooth count of MOR 1125 is evidence that Tyrannosaurus lost teeth through ontogeny, but the geological age of MOR 1125 brings this hypothesis into question. This could possibly prove that Nanotyrannus lancensis is a valid species, and Tyrannosaurus went through some minimal changes in its physiology and bone histology throughout its life. With its large orbits, Nanotyrannus could have occupied a nocturnal niche so that it can avoid competition with Tyrannosaurus. In order to compete with smaller predators such as dromaeosaurs and troodontids, Nanotyrannus could have also evolved to mimic a juvenile Tyrannosaurus by evolving a similar body plan. In order to prove our hypothesis feasible, we examine the rivalry between these two tyrannosaurs and their evolutionary history. We also will be examining any physiological and osteological differences between the skulls of known juvenile specimens of members of the subfamily of Tyrannosaurinae, and compare them to the holotype skull of Nanotyrannus and “Jane”.