Osteology, relationships and paleoecology of a new Arctic hadrosaurid (Dinosauria: ornithopoda) from the Prince Creek formation of Northern Alaska

Abstract

The Liscomb Bonebed (LBB), found in the early Maastrichtian Prince Creek Formation of northern Alaska, is the single most productive site for the Arctic dinosaurs in either hemisphere. From the LBB, thousands of bones representing at least hundreds of individuals of a saurolophine hadrosaur have been collected, but they have not been previously described and their taxonomic status remains unresolved. In part, this stems from the fact that most material comes from individuals approximately one-half to onefourth of adult size. Another long-standing question concerns whether dinosaurs in the Prince Creek Formation overwintered in the paleo-Arctic or migrated elsewhere (presumably south) to escape prolonged darkness and cold. Here, I attempt to determine the taxonomic status of the LBB hadrosaurs using three semi-independent methods: 1) geometric morphometric analysis; 2) comparative morphological analysis; and 3) cladistic analysis. An important component of this work also includes an ontogenetic study of the growth patterns of the genus Edmontosaurus, to which this material has been previously referred, in order to better understand ontogenetic variation within the Alaskan taxon. My results indicate the Alaskan taxon is a new species of the widespread genus Edmontosaurus. For the first time, the Alaskan taxon is described in detail, making it the best known polar dinosaur to date. My cladistic analysis suggests a possible biogeographic scenario in which the common ancestor of Edmontosaurus and Shantungosaurus originated in eastern Eurasia and then dispersed by the Campanian to North America via a land corridor in the area of present day Alaska. Finally, I used a novel method involving strontium isotope geochemistry to test the migration hypothesis of the new species of Alaskan Edmontosaurus. I measured strontium in tooth enamel of Edmontosaurus and a putative non-migratory species (Troodon) using LA-MC-ICP-MS. My results suggest diagenesis had not significantly altered the signal and that Alaskan Edmontosaurus likely did not migrate during approximately the last four months of life. My results lend further support for the existence of a distinct, early Maastrichtian polar dinosaur fauna known as the Paanaqtat Province.