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A reconstruction of Deinonychus showing how this dinosaur walked on two-toed feet. Photo by AStrangerintheAlps, image from Wikipedia.

When I think of theropod tracks, the mental image that immediately pops up is of three-toed depressions with conspicuous indentations where the dinosaur’s claws dug into the substrate. After all, theropod means “beast foot,” and many theropod tracks seem to fit the name. But not all theropod dinosaurs balanced on three toes. The deinonychosaurs–the group of sickle-clawed dinosaurs that included the more slender troodontids and the bulky hypercarnivorous dromaeosaurids–ambled through the Mesozoic on two toes, with their curved switchblade claw held off the ground. Over the past two decades, paleontologists have found these two-toed tracks at multiple sites around the world. Most, however, have been found in China, and researchers have just issued a profile of one of the richest deinonychosaur tracksites anywhere.

The in-press Acta Palaeontologica Polonica study, written by Lida Xing and colleagues, describes an Early Cretaceous tracksite at the Liujiaxia Dinosaur National Geopark in Gansu Province, China. The site preserves 71 deinonychosaur tracks. These footprints are unique enough that the paleontologists gave them a new name–Dromaeosauripus yongjingensis. It may seem strange to name tracks, especially since we don’t know exactly what species of dinosaur made them, but trace fossil experts name particular types of tracks to keep track of the different kinds of animals that left the impressions. If a track type is unique and consistent from print to print, then it often gets its own moniker.

Of course, tracks record fossil behavior. At the new site, at least two trackways show that individual dinosaurs turned while walking. Unlike other sites, though, there isn’t any evidence for social raptors here. Based upon the spacing of the tracks and other details, the paleontologists Xing and co-authors hypothesize that the deinonychosaur trackways were made by individual animals that walked along the same surface at different times.

But what kind of deinonychosaur made the tracks? This is the Cinderella Syndrome–fitting the right trace to the proper tracemaker. Unless a dinosaur literally dies in its tracks, paleontologists can only outline the general kind of dinosaur who left the footprints. In this case, the choice is between a troodontid and a dromaeosaurid.

Footprint size isn’t especially helpful. Most troodontids were relatively small, while dromaeosaurids could grow to 20 feet long or more. The footprints at the site were made by dinosaurs ranging from two to 10 feet long, and this means that the larger animals were close to the known upper limit for troodontid size. Frustratingly, size alone is too ambiguous to distinguish between a troodontid or dromaeosaurid trackmaker.

To narrow down the possibilities, Xing and collaborators turned to another clue. The toe lengths of troodontids and dromaeosaurids are slightly different. While the fourth (or outermost) toe of troodontids is slightly shorter than the neighboring third toe, the two supporting toes in dromaeosaurids are typically just about equal in length. The tracks at the site more closely match the dromaeosaurid pattern. Thanks to this tracksite, we can imagine feathery dinosaurs akin to Deinonychus strutting across Cretaceous China.

Reference:

Xing, L., Li, D., Harris, J.D., Bell, P.R., Azuma, Y., Fujita, M., Lee, Y.-N., and Currie, P.J. (2012). A new Dromaeosauripus (Dinosauria: Theropoda) ichnospecies from the Lower Cretaceous Hekou Group, Gansu Province, China Acta Palaeontologica Polonica DOI: 10.4202/app.2011.0115

A high-kicking Utahraptor outside the College of Eastern Utah's Prehistoric Museum in Price. Photo by the author.

Prior to the summer of 1993, “raptor” was synonymous with “bird of prey.” If you said “raptor,” whoever you were talking to knew you were talking about some kind of hawk, owl, eagle or other sharp-taloned aerial predator. Then Jurassic Park came along. Thanks to some taxonomic muddling and abbreviation, the cunning, sickle-clawed villains of the film’s third act immediately came to be known as “raptors.” Velociraptor, Deinonychus and kin had stolen the term for themselves.

Among non-avian dinosaurs, raptor might refer to the entire group of feathery coelurosaurs with grasping hands and hyperextendable toe claws—the deinonychosaurs—or to a specific subset of that group, called dromaeosaurids. It depends on where you care to draw the line. Just like its use among avian dinosaurs, the word “raptor” is informal and is a quick way to draw a conceptual outline of any dinosaur similar to Velociraptor.

But not everyone is happy with how “raptor” has been co-opted. A few months ago, paleontologist and Tetrapod Zoology author Darren Naish wrote:

Oh, and can everybody please stop using the word ‘raptor’ as a popular term for deinonychosaur, or dromaeosaurid? Admittedly, this rarely causes confusion, but it looks dumb and naive given that THE WORD RAPTOR IS ALREADY IN USE FOR ANOTHER GROUP OF ANIMALS. It would be like deciding to call sauropods ‘elephants’ or something.

And earlier this week, a reader sent me an email questioning the Los Angeles Times‘ use of the word raptor to describe a new genus of dromaeosaurid found in the Early Cretaceous rock of Utah. If birds of prey had claim to “raptor” first, and the term is just a bit of pop culture fluff, should we drop the word and push for deinonychosaur instead?

I don’t think so. Even though some informal dinosaur terms make me cringe—such as “parasaur” for Parasaurlophus and “Trike” for Triceratops—I think “raptor” provides a useful hook. To borrow a bit from another Steven Spielberg monster flick, you say “deinonychosaur,” and people say “Huh? What?” You say “raptor,” and your audience immediately has a general image of what sort of dinosaur you’re talking about. Rather than lament the reapplication of the word raptor as misappropriation or dumbing down, we might as well take advantage of the instant recognition the word triggers when trying to communicate with people who are not up on the latest theropod phylogeny. Almost twenty years after Jurassic Park debuted, it’s a little late to put “raptor” back in the cage.

More than that, I think “raptor” is a perfectly wonderful term for dromaeosaurids, if not deinonychosaurs as a whole. Not only has the “raptor” suffix been used in numerous dromaeosaurid names—Velociraptor, Utahraptor, Bambiraptor, Pyroraptor, Microraptor and so on—but these feathery dinosaurs were close cousins of the lineage which spawned the first birds. Some dromaeosaurids may have even hunted like avian raptors, using their huge tow claws to pin down prey rather than slash at it. Since “raptor” was always an informal term that applied to various lineages of avian dinosaurs anyway, I think it’s perfectly legit to use the word for the more ancient, non-avian precursors of today’s formidable falcons and eagles. Avian and non-avian raptors were dinosaurs of a feather.