Laelaps has an interesting post about the discovery of new dinosaur species over on the Phenomena blog at National Geographic. We don't know how many different dinosaur species existed during the reign of non-avian dinosaurs from about 235 million years ago to the mass extinction some 65 million years ago. New dinosaurs are being described all the time, at a rate of about one every 2 weeks. The latest was a new tiny, tyrannosaur from Uzbekistan was introduced to the world last week. If the the current estimates are correct, there are plenty more still in the ground waiting to be found.
Even then, most of what we know about dinosaurs comes from their skeletal remains. This lets us tell the difference between Tyrannosaurus and Triceratops, but, like some modern birds and reptiles, some non-avian dinosaur species may have differed only in color, geographic range, or other squishy features that we just don’t have access to. Even if we had the bones of every single dinosaur, we’d still probably underestimate the true number of species.
Still, given these caveats, University of Oslo researchers Jostein Starrfelt and Lee Hsiang Liow have created a new model they call TRiPS to estimate how many dinosaur species were around during the Triassic, Jurassic, and Cretaceous chapters of their history.
Drawing from known dinosaur records in the Paleobiology Database, the researchers extended the known record into estimations of origin and extinction for dinosaur species throughout their history and included a simulation of how likely it’d be for species to enter the fossil record.
In all, Starrfelt and Liow write, the heyday of the dinosaurs saw the comings and goings of about 1,936 different species. About half this count are expected to be theropods—the lineage that includes T. rex and birds—with the rest split between the long-necked sauropodomorphs and ornithischians such as the armored, horned, and duckbilled dinosaurs.
Starrfelt and Liow acknowledge that they’re dealing with estimates and that refinements will likely alter their dinosaur count. But, for a first run, the results came out similar to what’s been proposed before. In 2006 paleontologists Steve Wang and Peter Dodson estimated that around 1,844 genera of dinosaurs lived during the Mesozoic. While the categories are different—a genus can contain multiple species, like Triceratops horridus and Triceratops prorsus—many dinosaurs described so far are what paleontologists call monospecific, or have only one species in a genus. This affects estimates drawn from the known span of dinosaur discoveries, and might be why the species count isn’t even higher.
