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.


But Kansas has things like this:

Xiphactinus, specifically the famous "fish within a fish" fossil, from oceansofkansas.com
And this:

Wonderful skull of Mosasaurus, also from oceansofkansas.com

But you'll note that top thing is a fish, and the bottom thing is a marine reptile. What are marine animals doing in Kansas, which is in the middle of the North American continent? Well, here's a piece of trivia you can use to amaze your friends and befuddle your enemies: During a large portion of the Late Cretaceous period, part of North America was underwater.


This explains why so much of the midwest is flat: it was once a seabed.

The oceans went through a considerable period of seal level rise during the mid-to-late Cretaceous period, spanning the entirety of the Campanian, but draining to the south prior to the Maastrichtian. It actually originated in the north AND the south--there was some spillage on the Arctic Ocean side, and some spillage on the Gulf of Mexico side, and eventually the two inland seas joined and became the Western Interior Seaway (or Sundance Sea). Its maximum depth fell between 800 and 900 feet--shallow for sea, but it managed to divide North American in two: Laramidia in the west and Appalachia in the east. Notice that Laramidia got short-changed in terms of livable land area: for the most part, the subcontinent was a paradise for mountaineers, but if you lived in the coastal lowlands, you were affected by the constant ebb and flow of the western coast of the WIS.

And yet, paradoxically, this is where the majority of North America's Campanian dinosaur fauna is found. Virtually the entirety of the Ceratopsidae, minus Sinoceratops (Chinese) and the Triceratopsini (Maastrichtian), lived along this vertical coastline, as did most other Late Cretaceous groups like tyrannosaurs, deinonychosaurs, hadrosaurs, ankylosaurs, and pachycephalosaurs. The WIS itself was home to many mosasaurs, plesiosaurs, sea turtles, sharks, fish, and ornithocheirid pterosaurs. 

The next few posts will discuss the Laramidian ceratopsid fauna, specifically regarding the very interesting theory of Laramidian endemism and recent challenges to that theory.

But this is the basis--North America cut in two by a large inland sea. Bet you'll never look at Kansas the same way again.

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