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Edmontosaurus skull growth--adios Anatotitan

From: Ben Creisler

New in PLoS ONE:

Campione, N.E and Evans, D.C. (2011) 
Cranial Growth and Variation in Edmontosaurs (Dinosauria: Hadrosauridae):
Implications for Latest Cretaceous Megaherbivore Diversity in North America.
PLoS ONE 6(9): e25186. 

The well-sampled Late Cretaceous fossil record of North America remains the
only high-resolution dataset for evaluating patterns of dinosaur diversity
leading up to the terminal Cretaceous extinction event. Hadrosaurine
hadrosaurids (Dinosauria: Ornithopoda) closely related to Edmontosaurus are
among the most common megaherbivores in latest Campanian and Maastrichtian
deposits of western North America. However, interpretations of edmontosaur
species richness and biostratigraphy have been in constant flux for almost
three decades, although the clade is generally thought to have undergone a
radiation in the late Maastrichtian. We address the issue of edmontosaur
diversity for the first time using rigorous morphometric analyses of
virtually all known complete edmontosaur skulls. Results suggest only two
valid species, Edmontosaurus regalis from the late Campanian, and E.
annectens from the late Maastrichtian, with previously named taxa,
including the controversial Anatotitan copei, erected on hypothesized
transitional morphologies associated with ontogenetic size increase and
allometric growth. A revision of North American hadrosaurid taxa suggests a
decrease in both hadrosaurid diversity and disparity from the early to late
Maastrichtian, a pattern likely also present in ceratopsid dinosaurs. A
decline in the disparity of dominant megaherbivores in the latest
Maastrichtian interval supports the hypothesis that dinosaur diversity
decreased immediately preceding the end Cretaceous extinction event.

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