Hey there every peoples!
The Great Dinosaur Rush of the late 19th and early 20th century left few Mesozoic rocks unturned. Every now and then a new formation would be explored and new dinosaurs would be published. And just when it appeared that we had found all there was to be found, newly explored exposures in Utah began to capture the imagination with an explosion of new species. One of these exposures, the Kaiparowits formation, has gotten loads of media attention not just for its new species but also for its place in the big picture of dinosaur evolution.
The Kaiparowits formation is about 75 to 72 million years old, which means it was from the time when North America was actually two continents cut in half by a shallow sea (which is why marine fossils are discovered in places like Kansas, Nebraska, and Alberta). The two continents have been dubbed Appalachia for the eastern half and Laramidia for the western half. Not much is known about Appalachia due to a poor fossil record. However Laramidia is much better known thanks to such well known deposits as the Dinosaur Park formation in Alberta and the Two Medicine and Judith River formations in Montana. For a long time this was all we knew of Laramidia, and since both regions harbored very similar dinosaur faunas, it was assumed that this must have been the fauna for the whole of the continent (especially since the same dinosaurs were being found in Alaska). But the last 10 or so years has seen this trend turned on its head.
A map of ancient North America, with Laramidia to the west (image from Wikipedia)
As scientists started probing deposits further south, like the Kaiparowits in Utah, the Kirtland formation in New Mexico, and the Aguja formation in Texas, a different picture emerged. While the north had a fairly uniform dinosaur fauna, different regions of the south had each had their own unique collection of species, with a few of the same species from the north. For example, in the north the tyrannosaurs were comprised of Albertosaurus and Daspletosaurus. But New Mexico had its own tyrannosaur, Bistahieverser, and Utah harbored an as yet unnamed species of tyrannosaur. This phenomenon has been dubbed “Dinosaur Provincialism” and has seen more and more support as more fossils are described. But this has all been going on in the east of Laramidia? What about the western half of the “Lost Continent”? Why have the dinosaurs of the west received so little attention in the discussion of Laramidia and dinosaur provincialism?
The simple answer is: the west coast is a horrible place for dinosaurs. It’s a horrible pace for dinosaurs for the same reason as the Midwest. Like the Midwest, a lot of the west coast was covered by shallow sea, an environment dinosaurs did not inhabit. What is more, this shallow sea lapped at the base of a mountain range. While dinosaurs surely lived in said mountains, mountains are very bad environments for the preservation of fossils. As bones are washed down in mountain streams they get tossed around and destroyed so that by the time they reach a flood plain or the ocean there is almost nothing left to be preserved. But low and behold dinosaur fossils have been found on the west coast! They may be few and fragmentary but they are nonetheless dinosaur fossils! And they almost appear to throw a monkey wrench in the idea of dinosaur provincialism. Stay tuned for part 2 of “Forgotten Dinosaurs of the Lost Continent” where we’ll look at the beasts themselves!
Till next time!
A Central Coast Paleontologist 