Marsh’s “Megalosaurus” From Utah

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In 1988, a little more than a century after O.C. Marsh first described it, Allosaurus was declared to be the state fossil of Utah. What fewer people know, however, is that seven years before Marsh named the famous theropod dinosaur, he had discovered the signs of another predatory dinosaur.

According to an account written by Sue Ann Bilbey and James Evan Hall for Vertebrate Paleontology in Utah, in the summer of 1870 Marsh and a dozen of his Yale students trekked from Wyoming down into what would eventually become northern Utah. (The Beehive State was not admitted to the union until 1896.) They did not stay in any one place very long, but as they traveled they observed many of the fossil deposits around the Uinta Mountains in the northeastern part of the state, eventually making it into the vicinity of what is today Dinosaur National Monument.

As Marsh and his students descended from the mountains, they came across an area of tilted strata documenting parts of the Cretaceous and Jurassic. By following the succession of rocks the field team could travel through time, and they discovered fish scales, turtle parts, and the teeth of a dinosaur Marsh described as "resembling those of Megalosaurus." This was the first scientific citation, albeit a brief one, of a predatory dinosaur from Utah, and it would be nearly half a century before anyone would publish anything more on theropods from Utah. Indeed, even though paleontologists would eventually discover that Allosaurus remains were abundant in the state, the genus was described in 1877 on the basis of bones found in Colorado. The numerous dinosaur quarries elsewhere kept naturalists from fully exploring the dinosaur-age deposits of Utah until the turn of the 20th century. 

Unfortunately, what Marsh's "Megalosaurus" actually was remains a mystery. During the late 19th century many teeth and other fossilized scraps were attributed to Megalosaurus, a theropod from the United Kingdom which was the first predatory dinosaur to be formally described, but this was mostly because paleontologists were only just beginning to understand that the dinosaurs of North America were different from those found in Europe. It is almost certain that the teeth Marsh mentioned were not from Megalosaurus at all, but even after Bilbey and Hall relocated the site Marsh described, they did not find anything more that would allow them to precisely identify the dinosaur.

Much of the early history of paleontology is like this. Naturalists did not usually stumble upon nearly-complete skeletons just waiting to be picked out of the rock, but instead puzzled over various bone fragments and teeth. We often celebrate the big discoveries, the ones which gave us creatures with familiar names (like Allosaurus), but it was more enigmatic scraps that had set fossil hunters on the trail of such creatures in the first place.

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