By now, we’re all familiar with this image: Velociraptors running at high speed toward a big lumbering dinosaur that the little demons subdue with an onslaught of murderous slashes from an outsized claw on their second toe. Mark Stevenson’s reproduction below is a vivid attempt to bring one of these battles to life.
This model by artist Charlie McGrady illustrates the unique foot structure of this group of dinosaurs. The first toe has moved back, and toes 2, 3, and 4 point forward. It’s that second digit (the “inside toe”) that has been greatly enlarged to support that famous sickle-shaped claw that we’re now so used to seeing elevated when the animal runs and swiped down to cut a huge slash in attack mode.
That basic toe structure is represented in modern birds. In a perching bird’s anisodactyl foot, digit 1 is moved to the rear, while digits 2–4 face forward. Generally, as illustrated with this Clark’s Nutcracker, there is nothing remarkable about the 2nd digit – it’s about as robust as the 4th, and usually shorter than the 3rd (“middle” toe).
In some birds with anisodactyl feet, however, the 2nd digit is enlarged, and it plays a big role in survival. In many (most?) of our modern birds of prey, digit 2 is enlarged and bears a larger talon than on digits 3 and 4. While this is not all that noticeable on smaller raptors, it’s really obvious on the big, powerful eagles. You can see it on this Red-shouldered Hawk:
You can really see it on this Ornate Hawk-Eagle:
Recently, some out-of-the-box-thinking paleontologists have taken another look at Velociraptor feet and made a connection to the enlarged 2nd digits of modern birds of prey. Rather than just assume that the “switchblade” model was unassailable, they looked at how modern raptors use their enlarged #2s and did some comparative anatomy with Velociraptor (specifically Deinonychus) fossils. Led by Denver Fowler at the Museum of the Rockies, Montana State University, the team just published their new interpretation of these fossils in the journal PLoS One.
Fowler et al. 2011
One of the things that didn’t seem right to the team was that the reconstructions of fleet-footed raptors running down their prey was a bit incongruous with the structure of the foot. Rather than being elongated as in most cursorial species, the metatarsals (long foot bones) of Deinonychus were short, broad, and robust. If anything, these feet were built for strength, not for speed. The authors propose that the famous sickle-claw of raptors was used to grasp and hold prey about as large as the predators themselves, rather than as disemboweling rapiers designed to bring down prey many hundreds of times heavier. Instead of sprinting after prey like a cheetah and slicing it open like a Smilodon, the authors suggest that Deinonychus was more like a modern lion in hunting technique: quick ambush followed by a death-like grip.
OK, paradigm shifts are always fun, but this gets even cooler. Note that with the 1st and 2nd digits anchoring together to hold the prey, a modern bird of prey (and perhaps a raptor) can often struggle to stay balanced atop its kill, and it flaps its wings to stay upright and on top. Even modest feathered surfaces far too small to get the bird aloft can provide stability when the arms/wings are flapped. Could this explain what those feathered dinosaurs were doing with their rudimentary wings? Could flapping have evolved before flight? Might enough flapping capable to lift a bird up and away from its own predators and competitors have conferred a great advantage on those individuals able to do it?
The paper is a fascinating read, though I lack the paleontological chops to really make sense of it. I am a bit puzzled about how the “death grip” might have worked given the reduced 1st digit (the “hind toe”) of Deinonychus. Hopefully, some other folks will address that in the coming years and we’ll get to see if this new interpretation of dinosaur feet has any legs.