Last summer, while spending a day with paleontologist Joe Peterson and his crew at the Cleveland-Lloyd Dinosaur Quarry, I was lucky enough to find a dinosaur tooth. The shiny fossil had once fit into the mouth of a beaky herbivore called Camptosaurus, and, 150 million years later, was nothing more than an isolated crown. The tooth either broke off as the dinosaur fed, or snapped off the root sometime after the animal’s death.
I’ll probably never know how the tooth became divorced from the Camptosaurus jaw, but the nature of the Jurassic site where it rested indicates that the tooth probably did some postmortem traveling. Originally viewed as a mucky death trap where dozens of Allosaurus and other dinosaurs perished, newer analyses of the eastern Utah fossil site’s geology indicates that the numerous dead were washed together after death. (Which, in a new way, makes the overabundance of Allosaurus at this place even more mysterious.) The Camptosaurus tooth is just one small part of a greater aggregation of skeletal pieces that all flowed together when the Jurassic wet season ended the regular droughts that parched the ancient floodplains.
The backstory of a single tooth might not seem all that important, but how fossils came to be preserved as they are is an essential aspect of reconstructing prehistoric life. Fossils from bonebeds like Cleveland-Lloyd – as well as places called microsites that yield troves of teeth and other small petrified pieces – are sometimes used to take a census of who was living in an environment at a particular time, or what the demographics of prehistoric species were. And in dinosaur bonebeds, especially, shed carnivore teeth are often taken as solid evidence of scavenging. Such studies hinge on the idea that these fossils did not travel far from where the actual animals lived and died. A new study by Peterson, Jason Coenen, and Christopher Noto reminds us that we can’t take such scenarios for granted.
To see how Jurassic remains might have traveled, Peterson and colleagues put dinosaur tooth casts to the test in a flume. The researchers placed high-density urethane resin casts of an Allosaurus tooth and Camarasaurus tooth – with and without roots – in a small flume to see how they’d travel by water. All the teeth traveled, most between five and twelve inches, with the un-rooted Camarasaurus tooth being the distance champion at traveling about three feet.
These distances might sound small, but this is a test to see how different details of flow and shape affect how dinosaur teeth travel. Teeth with some shapes, such as un-rooted Camarasaurus teeth, probably slid and tumbled further than others as Mesozoic waters moved and buried dinosaurs. This is going to alter how paleontologists use isolated teeth in studying dinosaurs. If an assemblage contains teeth that are more-easily transported, and the site shows signs of active water transport, then those teeth may not be the best to use in trying to reconstruct feeding or other behaviors at that particular site. Paleontologist Matt Bonnan made this point in response to a paper on possible sauropod migration inferred from evidence gleaned from Camarasaurus teeth. We must understand dinosaurs in death before we can properly bring them back to life.
Peterson, J., Coenen, J., Noto, C. 2014. Fluvial transport potential of shed and root-bearing dinosaur teeth from the late Jurassic Morrison Formation. PeerJ. 2:e347 http://dx.doi.org/10.7717/peerj.347