The Long, Complicated History of Appalachian Ceratopsians

North America during the Campanian

The title is a joke. Finding ceratopsian remains east of Texas is an incredibly recent phenomenon. Oh sure, there are plenty of (fragmentary) dinosaurs known from the eastern half of the United States, but those taxa tend to be tyrannosauroids, nodosaurs, ornithomimids, and hadrosaurs. I should mention at this point that, during much of the Late Cretaceous, North America was cleaved into three islands by the presence of a shallow interior sea called the Western Interior Seaway (WIS): Laramidia to the west, Nunavut to the north, and Appalachia to the east. Laramidia’s eastern north-south shoreline is where we get most of North America’s dinosaurs—Alberta, Montana, Utah, and (to a lesser extent) Texas are all hotbeds of dinosaur action, and that includes ceratopsians.

Aquilops in My Hand

Aquilops americanus, by the incomparable Brian Eng.

There's a new basal neoceratopsian in town. It's from Montana's Cloverly Formation, and it's a raccoon-sized critter that is the oldest definitive horned dinosaur in North America: Aquilops americanus, an eagle-faced cutie. It was described by Andy Farke, Desmond Maxwell, Richard Cifelli, and Matthew Wedel. Andy wrote about it at The Integrative Paleontologist, and Matt Wedel has been covering it extensively--as well as public outreach--at SV-POW. Check it all out.

Laramidian Endemism, Part 2

Last week we saw that, during a good portion of the Late Cretaceous, North America was divided into two unequal halves by the shallow Western Interior Seaway (WIS). Those dinosaurs on western Laramidia were boxed between mountains to the west and the fluctuating coastline of the WIS to the east. They lived on a narrow, vertical strip of land running from Alaska’s North Slope to Mexico. On the other hand, everybody had beachfront property. We can’t say much about Appalachia’s Mesozoic composition, as much of its fossil-bearing rocks were destroyed by the last Ice Age. However, tyrannosaurs and hadrosaurines who were isolated prior to the formation of the WIS evolved along different lines than their western relatives. Dryptosaurus and Appalachiosaurus are the island continent’s aberrant tyrannosaurs. Hadrosaurus and a few potentially dubious genera (Lophorhothon, Hypsibema) represent the area’s hadrosaurine population. It’s ironic that, despite the area’s drastic surface area deficit, Laramidia is ridiculously rich in dinosaur fossils whereas Appalachia is not at all.

Taxonomic Messes

In his recent Princeton Field Guide to Dinosaurs, Greg Paul did something interesting: he sank most of the Centrosaurinae into Centrosaurus. Thus, instead of Styracosaurus albertensis, you now have Centrosaurus albertensis. Where once there was Pachyrhinosaurus lakustai, there is now only Centrosaurus lakustai. This seems ridiculous on the face of it, but Paul's justification is not entirely off-kilter: he surmises that the Centrosaurinae exhibits as much or less variation than is found between different species of Varanus. But that comparison is, in itself, completely arbitrary. The taxonomy of living animals--and especially living reptiles--is dictated by an entirely separate group of specialists. If paleontologists were in charge of Varanus, it might well be divided into separate genera. Herpetologists (and Greg Paul) are especially fond of subgenera, whereas as I believe that subgenera are confusing and unnecessary.