Earlier I covered in detail the plumage
of deinonychosaurs ("raptors") and the many errors that often occur in artwork featuring them. Here, I'll talk about the function of their hands.
It is a popular idea that deinonychosaurs could use their hands to hold things. This is partly true. Deinonychosaurs could hold things two handed with the wrists flexed and bring food up to the mouth. However, they couldn't hold things with just one hand. The only known exception to this is Bambiraptor feinbergi
, which could do this by pinching its first and third fingers together.
Deinonychosaurs had another way of holding things, and that was clutching towards the chest. They could only do this one handed. It's important to note that deinonychosaurs had big feathers attached to their second finger. This wasn't a problem when holding things two handed, because the feathers point down while the palms of deinonychosaurs face inwards most of the time. When deinonychosaurs clutched objects to the chest, however, the wrist extended. And when this happened, the palm rotated to point upwards. If a deinonychosaur tried to use both hands to clutch towards the chest, one wing would block the other. By the way, it might also be important to note that some deinonychosaurs, particularly the small flying ones like Microraptor zhaoianus
, had such long primaries that they probably had to hold their hands out to the sides or the feathers would drag on the ground. These deinonychosaurs probably didn't use their hands for manipulating things much at all, probably only using their wing claws to help them climb trees.
Some people refuse to put feathers on the heads of deinonychosaurs for the reason that cleaning the head may have been problematic. But deinonychosaurs had no difficulty in reaching and cleaning the head with their wing claws. They could reach back and scratch their legs, too. They couldn't scratch their backs with their wing claws, but they could probably manage that with their teeth. Note that different deinonychosaurs had different limb proportions. Deinonychus antirrhopus
could only bring food to its mouth or scratch its head when its head was lowered, but Bambiraptor feinbergi
could reach its face even with its head upright.
Deinonychosaurs may have been able to reach for prey items hiding inside crevices with their fingers. However, they could only do this with the third finger and if the surface they were probing was perpendicular to the direction the palm was facing, or the wing feathers would have gotten in the way. They couldn't use the second finger because of the feathers attached to it, and the first finger was too short.
It's likely that deinonychosaurs could swing their forelimbs back and forth to use their wing feathers in a visual display.
Because of the wing feathers, deinonychosaurs couldn't get their hands anywhere near the ground. They couldn't dig with the wing claws or pick up objects from the ground. Traces of deinonychosaurs digging for mammals have been identified, and they use the foot claws for this activity instead. And I can only suppose that they only used their hands for holding food if it was too big to be swallowed in one piece or if the mouth was preoccupied with something else such as snapping at a rival. Therefore, the manipulation of objects by the hands would've played a largely secondary role to the jaws.
Edit: Just found out that this was mentioned
on TV Tropes. Thanks for the recognition!