What Is a Dromaeosaur? The Claw Was Probably Not for Slashing

Dromaeosaurs are small to medium theropods characterised by a stiffened tail, a large brain relative to body size, long grasping arms and an enlarged sickle-shaped claw on the second toe, held clear of the ground while walking so that it stayed sharp. That claw was long interpreted as a slashing weapon for disembowelling prey, an image that dominated reconstructions for decades. Direct testing has undermined it: experiments driving replica claws into flesh found they puncture and grip rather than cut, since the inner edge is rounded rather than bladed, and the claw's cross section is unsuited to slicing. The favoured explanation now is prey restraint, with the animal mounting a smaller victim, driving the claws in to hold it and using body weight and flapping forelimbs for balance while feeding, a behaviour observed in modern birds of prey and given the name raptor prey restraint. A famous fossil preserving a dromaeosaur locked with a horned dinosaur shows the claw at the victim's throat, which fits gripping better than slashing.

The gap between the popular image and the animals is specific and worth listing:

• •Size, since the species that gave its name to the film creatures was roughly turkey-sized, and the creatures depicted are closer to a larger relative described in the same period
• •Feathers, which are now known from direct fossil evidence in several dromaeosaurs including full flight feathers on the arms and tail, so these were feathered animals rather than scaly ones
• •Forelimb posture, since the wrists could not pronate to hold objects palm-down, and the hands faced inward as a bird's wings do
• •Pack hunting, which is asserted confidently and is weakly supported, resting mainly on an assemblage of individuals found together that may reflect a mass mortality rather than cooperative behaviour
• •Intelligence, which was high for a dinosaur and is frequently overstated, with brain size comparable to a modern bird rather than to a primate
• •The name itself, since the film's creatures are called by a genus whose actual members were small, which has permanently confused public usage

The group sits among the closest known relatives of birds, and the shared features are extensive. Several members had asymmetrical flight feathers of the kind that generate lift, which is a functional signature rather than a decorative one. Microraptor had long feathers on all four limbs and is generally reconstructed as a glider, which suggests that flight or gliding was arrived at more than once in this part of the tree. Wing folding, brooding posture on nests, hollow bones, wishbones and sleeping with the head tucked all appear in the group. The disagreement now concerns not whether they are close to birds but how flight developed, with the ground-up and trees-down accounts both having support and a third option, in which flapping assisted running up steep surfaces, supported by observations of modern birds doing exactly that. The evidence increasingly suggests that the ancestors of birds were already doing several things with feathered forelimbs before powered flight appeared.

The group is an unusual case of popular culture driving scientific communication rather than following it. The films made a technical name a household word and fixed a set of images that palaeontologists have spent thirty years correcting, and researchers report that the feathered reconstructions in particular meet resistance from audiences who regard them as less frightening. At the same time the films are credited by many working palaeontologists with prompting a generation to enter the field, and the surge in interest coincided with a genuinely productive period including the discovery of the Chinese feathered dinosaur fossils that overturned the film's own reconstructions within a few years of release. The situation illustrates a general problem with communicating a field where the evidence changes, since an image that was defensible when created becomes wrong and yet continues circulating, and correcting it requires more effort than establishing it did.

The sickle claw punctures and grips rather than slashes, and the favoured reading is that the animal pinned smaller prey and fed while it was still alive, as modern birds of prey do. The best-known species was turkey-sized and feathered, with asymmetrical flight feathers in several members and a four-winged glider among them. Pack hunting is asserted far more confidently than the evidence supports.