October 2, 2012
The Early Jurassic is a mysterious time in dinosaur evolution. In North America, at least, paleontologists have uncovered scores of dinosaur tracks from this critical time when dinosaurs had been handed ecological dominance in the wake of a mass extinction, but body fossils are rare. In the orange sandstone that makes up so much of Arches and Canyonlands national parks in Utah, for example, only a handful of skeletons have ever been found. This formation–called the Glen Canyon, Navajo, Nugget or “Nuggaho” depending on who you ask–preserves immense sand dunes that recorded prehistoric footsteps but rarely bone. The recently described sauropodomorph Seitaad, and a group of as-yet-unnamed coelophysoids, are exceptionally rare finds.
Yet, from Connecticut to Arizona, there is one dinosaur that is constantly presented as an icon of dinosaurs circa 190 million years ago. This is Dilophosaurus–the 20-foot-long, double-crested theropod that gained dubious fame thanks to Jurassic Park. (Contrary to the film, there’s no evidence that this carnivore was a “spitter” with a collapsible neck frill.) At sites where Early Jurassic theropod tracks are found in abundance, Dilophosaurus is invoked as a possible trackmaker. But is this really so?
The remains of what would eventually be named Dilophosaurus were discovered in 1942 by Jesse Williams near Tuba City, Arizona. It took another 12 years before paleontologist Samuel Welles mistakenly attributed the bones to a new species of Megalosaurus –“M.” wetherilli–and the name Dilophosaurus itself wasn’t actually coined until 1970. Despite all this shifting around, though, Dilophosaurus wetherilli became a symbol of top Early Jurassic carnivores. Paleontologists had found plenty of Early Jurassic tracks made by a Dilophosaurus-size dinosaur, and now they finally had a body.
Frustratingly, though, we usually don’t know what dinosaur left a particular trace fossil unless the animal literally died in its tracks. While Dilophosaurus is a good fit for many large-size, Early Jurassic tracks, and may very well have left tracks at places such as St. George, Utah’s megatracksite, there’s no way to know for sure. And it seems unlikely that the same species of dinosaur that left tracks in Early Jurassic Utah also made footprints in the mud of what would become the Connecticut Valley. Who knows how many mid-sized theropods might have stalked lakeshores during this time? We don’t know, and the situation is made all the more irksome since the sediments which preserve tracks often don’t contain body fossils. We know these dinosaurs from the bottom of their feet but little else. Until future discoveries fill out the fauna of North America’s Early Jurassic, Dilophosaurus will remain the most familiar and iconic predator of its epoch.
Naish, D. 2009. The Great Dinosaur Discoveries. University of California Press: Berkeley. pp. 94-95
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