Today, Nic Campione and I published a paper in PLoS One on Edmontosaurus diversity and bisotratigraphy in North America. We took a morphometric approach to the problem, and analyzed almost all of the articulated Edmontosaurus skulls. Results suggest only two valid species, Edmontosaurus regalis from the late Campanian, and E. annectens from the late Maastrichtian. Several previously named taxa, including the controversial Anatotitan copei, were erected on morphologies now recognized to be associated with ontogenetic size increase and allometric growth. The most important aspect of this project is that we took a disparity approach, rather than subjective alpha taxonomy, to assess hadrosaur diversity in the latest Cretaceous of North America. Our results show a clear decline, due primarily to the absence of lambeosaurines in the Late Maastrichtian. It is almost certain that the same decrease in disparity applies to ceratopsids, too, because centrosaurines drop out of the record in the latest Maastrichtian. Regardless of how you view Triceratops and Torosaurus, or Anatotitan for that matter, megaherbivorous dinosaurs were probably less ecologically diverse in the dying days of the Cretaceous, at least in North America.
Citation: Campione NE, Evans DC (2011) Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae): Implications for Latest Cretaceous
Megaherbivore Diversity in North America. PLoS ONE 6(9): e25186. doi:10.1371/journal.pone.0025186