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Fishing Dinosaurs at the St. George Dinosaur Discovery Site
Meat-eating dinosaurs fed on fish along the shores of an ancient lake near St. George, Utah, approximately 198 million years ago. The valuable fossil evidence was found in the vicinity of the St. George Dinosaur Discovery Site at Johnson Farm (SGDS) in southwestern Utah. Much of the area used to be covered by the Lower Jurassic Lake Dixie which provided food for the theropod or meat-eating dinosaurs. The story of these fossils was just published in Utah Geological Survey's September 2007 issue of Survey Notes (Volume 39, Number 3). The article is entitled, The Case for fishing dinosaurs at the St. George Dinosaur Discovery Site at Johnson Farm by Andrew R. C. Milner (St. George City Paleontologist and SGDS Curator) and Dr. James I. Kirkland (State Paleontologist, Utah Geological Survey), with art work by Russell Hawley and Brad Wolverton.
The fossils, which are housed at the SGDS in St. George, Utah, were discovered in rocks made of sediment deposited in and around an ancient lake system called “Lake Dixie.” Fossils are rare from these rocks, called the Moenave Formation, but are relatively abundant in the St. George area. As a result, what life was like in this time period in western North America have been poorly known. Fossils from slightly older and slightly younger rocks in the southwest are well known in Arizona, New Mexico, and Texas, so these discoveries fill in an important gap.
A combination of important fossil finds at the SGDS, including the best preserved and largest collection of dinosaur swim tracks in the world, abundant fossil fish (semionotids, coelacanths, freshwater sharks, and lungfish), and rare theropod dinosaur remains all provide important clues into the feeding behavior of these carnivorous dinosaurs. Semionotid fish are the most common body fossils at the site, and they have enamel-coated scales forming a "chain-mail" armor covering. The larger theropod teeth and a well-preserved thoracic vertebra suggest this dinosaur was a close relative of Dilophosaurus, and was probably responsible for producing the larger Eubrontes tracks at the site. The tall, slender, and cylindrical teeth exhibit extensive wear patterns along the front and back serrated ridges. The authors hypothesize the may be the result of enamel-on-enamel wear produced by the dinosaurs biting through semionotid fishes. This Dilophosaurus-like dinosaur and Dilophosaurus itself share similarities to modern crocodiles and spinosaurid dinosaurs from the Early Cretaceous of North Africa that point to fish-eating habits. These fossils also explain the abundance of dinosaur swim tracks found at the SGDS.
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