There’s more than one way to make a significant dinosaur discovery. You can fill up water bottles, slather on sunscreen, and strike out across exposed stone in the hope that luck and a sharp eye will lead you to bones no one has ever seen before. That’s the traditional way. But museums have become metaboneyards where dinosaurs hide within plaster jackets and newspaper-lined drawers, forgotten until a lucky fossil hunter discovers them anew. This alternate sort of fossil hunting is what led paleontologists Michael Hanson and Peter Makovicky to uncover additional remains of a rare Jurassic carnivore.
During more than a century of discovery and research, paleontologists have identified at least three enormous carnivorous dinosaurs that roamed the lands of the American west around 150 million years ago. Allosaurus is the most abundant and most famous, challenged in pop culture notoriety by the gnarly and rare Ceratosaurus. But just as big and frightening is a little-known megalosaurid dubbed Torvosaurus.
Often found in the same quarries as Allosaurus, albeit in lesser numbers, Torvosaurus had long, deep skulls set with elongated teeth that they presumably put to work on the hides of sauropods. And that’s not to mention their short, stout forelimbs which bore a set of three wicked, recurved claws. No complete specimen has yet been found, but the bones discovered so far indicate this thirty-foot long predator prowled the Jurassic floodplains of Colorado, Utah, Wyoming, and, as recently realized, Portugal.
Despite the size and apparent rapacity of Torvosaurus, though, the dinosaur never gained the popularity of Allosaurus and Ceratosaurus. Perhaps that’s because the theropod was only named in 1979 – the classic Jurassic neighbors of Torvosaurus were named much earlier and had more time to gain iconic status. Maybe Torvosaurus could have joined them if earlier researchers knew what they had found.
The specimens that Peter Galton and Brooks Britt used to officially describe the dinosaur actually were not the first to be found. A very large Jurassic tooth collected in 1879 and not figured until a 1927 study, Galton and Britt proposed, may have been the first piece of Torvosaurus ever discovered by scientists. And now Hanson and Makovicky have identified another case of a Torvosaurus before its time.
Between 1899 and 1901, the Field Museum paleontologist Elmer Riggs led a crew on several expeditions to discover dinosaurs among the Freezeout Hills of southeast Wyoming. Riggs had been tipped off to the area by colleague Samuel Wendell Williston, and most of the sites Riggs’ team opened contained only one genus of dinosaur in each. Quarry 6 was different. This site was strewn with the fossils of “miscellaneous dinosaurs”, Riggs recorded in his notebook, including what appeared to be the sauropod Camarasaurus, the spiky-tailed Stegosaurus, and Allosaurus.
Not everything the team collected was opened or studied upon arrival at the Field, however. One particular jacket collected dust for over a century until a 2005 inventory of the museum’s collections turned up the historic specimen. When the fossils inside were finally exposed and cleaned, they were not the Allosaurus Riggs had suspected. By 1901, nearly eight decades before the animal would be named, Riggs’ team had found Torvosaurus.
The jacket didn’t contain much of the elusive dinosaur. Hanson and Makovicky report that the jacket included the left metatarsus – or long bones of the foot – a toe bone, a finger bone, and broken pieces of the dinosaur’s belly ribs. Still, the anatomy, size, and robust nature of the foot bones show that this was indeed Torvosaurus, which had a heftier build than the Allosaurus and Ceratosaurus the carnivore likely competed with for food. So far as is presently known, this was the first set of non-skull elements from the dinosaur to be excavated.
The belated discovery of Riggs’ Torvosaurus brings up a tantalizing possibility. Paleontologists have been collecting fossils from the Morrison Formation – in which Torvosaurus is found – since the late 19th century. And given that paleontologists often collect more than they ever get a chance to study themselves, there are probably unopened jackets that may contain more of Torvosaurus, not to mention the possibility of misidentified bones that rightly belong to this dinosaur. Paleontologists may have more of the dinosaur than they know. There’s even the chance that paleontologists have already found some pieces of young Torvosaurus.
Not only is Torvosaurus rare, but all the specimens known to date are from large-bodied, adult or near-adult individuals. As Hanson and Makovicky point out, this may because Torvosaurus is often recognized by the large, robust nature of the dinosaur’s bones. Yet dinosaurs changed dramatically as they aged, and young individuals of a species are sometimes confused as members of another. Perhaps elements of young Torvosaurus have already been found and mislabeled, especially since this dinosaur is more often found in multi-species bonebeds were isolated bones, rather than articulated skeletons, dominate.
The romance of paleontology is of discovery. To wonder about vanished lives that have been stripped down to the bone. Bringing dinosaurs out of the field is the first step in this ongoing quest, but as museums stores pile up, bonebeds kept on shelves and in drawers brim with mysteries and clues to rival sun-baked field sites.
Hanson, M., Makovicky, P. 2013. A new specimen of Torvosaurus tanneri originally collected by Elmer Riggs. Historical Biology. http://dx.doi.org/10.1080/08912963.2013.853056