GEOS 308- Paleontology

Richard Thompson- Guest Lecturer

date: 10-15-02

(A) Relevant Geologic History

· In the Jurrasic, the Faralon Plate subducts underneath the North American Plate, this caused mountain building and basin subsidence throughout the western US

· By the Cretaceous, a large basin called the Chihuahua Trough was formed and allowed the ocean to expand all the way up to southern Arizona from the Gulf of Mexico

· Around this same time, there were many rivers and a rift lake in southern Arizona

· Today, these Cretaceous environments are preserved in the sediments of southern Arizona. These preserved sediments, particularly the marine and lake deposits, are often fossiliferous (contains fossils)

· Uplift due to tectonic activity (i.e. mountain building) allows these fossiliferous beds to be exposed. Exposure makes it much easier to find the fossils, except for one thing: Arizona is so tectonically active that layers of sediment can be turned vertical or flipped over completely. This can make it very difficult to find all of the pieces of a skeleton, especially something as big as a dinosaur...

(B) Discovery and Excavation of Dinosaurs

· Again, tectonic activity is good for exposing fossils, but can create a lot of confusion if there is enough faulting to cause big blocks of sediment to be displaced

· Study geologic maps and talk to local geologists to find good spots for fossil hunting. Concentrate in areas where there are marine deposits, they tend to contain many fossils

· Through fossil hunting in southern Arizona, he has found:

(a) awesome dinosaur teeth- still have serrated edge. Black in color due to manganese

(b) Hadrosaur femurs- his first big find

(c) lots of nicely preserved vertebrae

(d) and, of course...his biggest find: Sonorasaurus thompsoni a new species of Brachiosaurus.

(C) Sociological Aspects of Making a Big Dinosaur Discovery

· Haggling over what kind of dinosaur it was....first identified as a Hadrosaur, then Jack Macintosh (an expert in long neck dinosaurs) identified the bones as a new species of Brachiosaurus...they named it Sonorosaurus thompsoni (after Rich Thompson, our guest lecturer and discoverer of the dinosaur)

· Sonorasaurus thompsoni had a wine named after it.... This was used as a promotion for the Desert Museum (a scientist from the Desert Museum led the excavation of the dinosaur and its fossils were brought back to the museum for restoration)

· Honorary M.S. degree and Ph.D. for the leader of the excavation

· Sonorasaurus thompsoni is nominated by the Desert Museum to be Arizona’s State Dinosaur.