Sometimes people who discovered dinosaurs had no idea what they had found. As recounted by paleontologist and historian Eric Buffetaut, for example, in 1824 the French naturalist Georges Cuvier illustrated what appeared to be a fossil crocodile tooth sent to him by the English paleontologist Gideon Mantell. Further searches of England’s Mesozoic rocks turned up similar teeth—attributed to a prehistoric crocodile Richard Owen named Suchosaurus in 1824—but what the 19th century scientists didn’t know what that the teeth actually represented a dinosaur. The Suchosaurus teeth belonged to one of the spinosaurs, a crocodile-snouted and sometimes sail-backed group of dinosaurs that began to be well understood by paleontologists after the 1986 description of Baryonyx. The European naturalists misidentified the dinosaur teeth because the complete skeletons necessary for them to make the correct, dinosaurian assignment for the teeth had not yet been found.

The changing identity of Suchosaurus is not the only example of mysterious bones later being recognized as belonging to dinosaurs. Othniel Charles Marsh initially mistook the horns of Triceratops for the armaments of a gigantic bison, and the recognition that the weapons belonged to a dinosaur helped establish the archetype of horned dinosaurs in the late 1880s. But even Marsh’s “bison,” found in 1887, was not the first specimen of a horned dinosaur to be discovered. Small pieces of the strikingly ornamented dinosaurs had been found at least three decades earlier.

John Bell Hatcher, one of Marsh’s cadre of paleontologists entrusted to describe the great horned dinosaurs, paid tribute to the earlier discovery of horned dinosaurs in his classic monograph The Ceratopsia. In 1855, Hatcher explained, the geologist and explorer Ferdinand Hayden picked up a variety of fossils from the strata around the mouth of the Judith River in central Montana. Today we know this area as a major center of Late Cretaceous dinosaur sites, but at the time, no one really knew the dinosaurian bounty that lay in the West, and the bits of pieces of the creatures were sent back to Philadelphia to be examined by the polymath Joseph Leidy.

Leidy thought that he could distinguish four different types of dinosaurs among the rather paltry remains, including that of a dinosaur he called Trachodon mirabilis—a name for one of the “duck-billed” dinosaurs that has since fallen out of use because the teeth are not distinctive enough to assign to a particular species. Given the unfamiliar nature of the fossils, though, it is no surprise that Leidy made a mistake in grouping the fossils. Among the lot Leidy attributed to Trachodon were single-rooted and double-rooted teeth. The single-rooted teeth were indicative of hadrosaurs—the type of animal Trachodon was traditionally reconstructed as—but the double-rooted teeth were later confirmed as belonging to horned dinosaurs. They could not have known it from such incomplete material, but Hayden had discovered and Leidy had described some of the first horned dinosaur fossils ever reported. As paleontologists discover more about dinosaurs, they create a richer context by which to compare old discoveries, and old puzzles finally gain solutions.

References:

Buffetaut, E. 2010. Spinosaurs before Stromer: early finds of spinosaurid dinosaurs and their interpretations. In Moody, R.; Buffetaut, E.; Naish, D.; and Martill, D. Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society, London, Special Publications, v. 343, p. 175-188

Hatcher, J.; Marsh, O.; Lull, R. 1907. The Ceratopsia. Washington: Government Printing Office. pp. 3-4