Tuesday, November 25, 2014

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.

Monday, November 10, 2014

Laramidian Endemism: Part 1

Every few years, the wife and I will spend Christmas away from Alaska with her family, in Kansas. Now, the Sunflower State may not be the most exciting place to spend the holidays, but it's usually warmer than it is in Anchorage. It's also, from my point of view, a lot more geologically interesting. Now, of course, Alaska is home to about a million mountain ranges, glaciers, and volcanoes. Indeed, my state is largely a conglomeration of chunks of continental crust, earthquakes, and volcanic activity. In its own way, Alaska is the MOST interesting state, geologically speaking. But Kansas is basically made of limestone and chalk. Alaska's Mesozoic fossil record is only impressive when you look past the fact that it is made up of hundreds of bits, pieces, and chunks of bone.

Tuesday, November 4, 2014

Deinocheirus > Spinosaurus

There’s a new giant, sail-backed, piscivorous theropod in town.

Just a month after Ibrahim et al. (2014) revealed their new interpretation of Spinosaurus aegypticus, Lee et al. have done one better: they've published a description of Deinocheirus mirificus, one of the most mysterious dinosaurs ever found. For those not keeping score at home, Deinocheirus was discovered in 1965 during a Polish-Mongolian expedition into the southern Gobi Desert. Unfortunately, all that was found was a pair of enormous arms—indelibly seared into the minds of every man, woman, and child who opened a dinosaur book over the next forty years. It was pretty easy to see that Deinocheirus was an ornithomimid, but it must have been absolutely enormous. It wasn't until 2006 and 2009 that more skeletal material was discovered—both in the field and in a private collection. For more on this, Ed Yong and Brian Switek have fascinating write-ups about the discovery and its history.