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Wednesday, March 25, 2009

The Untold Story of Hypsibema

With all the interesting dinosaurs coming out of China, the western U.S., South America, the Sahara, and other such areas lately, some other interesting finds have been rather overlooked. However, I find this one site quite fascinating, for a variety of reasons. The site is the Chronister site in Bollinger County, Missouri. Since 1999, the site has produced many fossils of animals from the Late Cretaceous, including fish, turtles, and the dinosaur Hypsibema missouriensis.

What exactly is Hypsibema missouriensis? Well, in short it is a hadrosaur trying very hard to be a sauropod. I have read in some texts (though I cannot, for the life of me, remember what they were) that Hypsibema was one of the largest hadrosaurs, while probably not as big as Shantungosaurus, certainly big enough to rival many of the other largest hadrosaurs of all time. In fact, it was so large that on its discovery it was mistaken to be a small sauropod. It was probably one of the largest dinosaurs of Eastern North America in its time.

But what makes Hypsibema so interesting? Simply put, the fact that it is from Eastern North America. During the Late Cretaceous, Eastern North America was separated from Western North America, by an interior seaway chock full of mosasaurs, plesiosaurs, killer fish, and pterosaurs and birds. The two land masses were isolated for some time (at least since the Turonian), and thus developed their own unique fauna. We know what the fauna of Western North America was during the Late Cretaceous, full of tyrannosaurs, ceratopsians, ankylosaurs, lambeosaurine and hadrosaurine hadrosaurs, etc.

But there comes a problem when we speak of Eastern North America. Fossils of dinosaurs in Eastern North America are not too common. We only have some fragments from Nebraska, Iowa, and Minnesota, this site from Missouri, some somewhat rich deposits in North Carolina, New Jersey, Maryland, and Alabama, and that is about it. Many of these are only complete enough for them to be identified as "theropod" or "hadrosaur". Even worse, there is little to no attention paid to these fossils, despite the fact that the first two American dinosaurs ever were discovered here, and we are literally sitting on a "lost continent" here. Nevertheless, we do know of what some Eastern North American dinosaurs were like. There were the dryptosaurs, primitive long-armed, three-fingered tyrannosaurs like Dryptosaurus and Appalachiosaurus, which were probably the dominant predators. One also sees nodosaurs, though as of yet we have been unable to identify them to the species level. And there are numerous hadrosaurs, including Hadrosaurus itself (which may be defunct), Hypsibema, and others.

About the site itself. Digs have been conducted there annually for quite some time now. In 1999 a greenhouse was erected over the site, allowing for year-round excavation. More fossils have been found since then, including crocodiles, turtles, more bones of Hypsibema, and two bones of theropods. More recently, a large block of bones was found, which contains vertebrae and other bones from a dinosaur (or else a very big croc), most likely belonging to Hypsibema. This interesting site should be kept an eye on, if for all else because it is one of the only dinosaur sites active in the Eastern U.S.


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