Archive for the Dromaeosauridae Category

Dromeosaurs may have hunted like eagles.

Posted in Accipitridae, Aves, Deinonychosauria, Deinonychus, Dinosaurs, Dromaeosauridae, Maniraptora, Paraves, Saurischia, Science, Theropoda with tags , , on December 23, 2011 by Paul Reinerfelt

On this day, when the darkness starts to recede again, it seems appropriate to reboot my blog.

A group of researchers from Montana have conducted an excellent study of the feet of Dromeosaurs (colloquially called “raptors”) and compared them to the feet of extant raptors (birds of prey). The result is surprising. The morphology of the Dromeosaur foot seems to indicate that they, despite Jurassic Park, did not run down their prey (as their cousins, the Troodonts did) and then kill it with a quick slash of the infamous “killer claw”. Instead, the team found that the Dromeosaur (specifically Deinonychus) foot most resembled that of extant Accipitridae (hawks and eagles). Interestingly, these raptors often capture prey that is too big to fly away with. Instead, they subdue their prey by staying on top, anchoring themselves with their enlarged second toe, pinning down the victim with their body weight. Meanwhile they start tearing at it with their beaks, exposing skin and effectively starting to eat their prey while it still lives! (I believe the word is “Ouch!”.) Needless to say, the victim does not stay alive for long after the raptor has started eating, blood loss and organ failure quickly puts an end to the agony.

So, it seems probable that Dromeosaurs did something similar. Their feet are comparatively robust and more built for strength that speed, consistent with a grasping function. The hypertrophied DII claw is sunk deep into the prey, anchoring the animal so it has less chance to escape. Meanwhile, what does the Dromeosaur do?

This is where it gets really interesting, to keep itself on top of the victim, the Dromeosaur would be flapping its arms to retain its balance. We know that the Dromeosaurs wore feathers, possibly longer on the arms. The vigorous stability flapping typically executed by the raptor in order to first get on top of its prey, then to constantly maintain this position, allowing it to use its full bodyweight to pin its victim to the ground, is suggested by the research-group to be the precursor to wing-flapping needed for flight! It provides a plausible explanation for pre-flight flapping as well as a reason for the arm-feathers to become enlarged. This is because, when not flapping, the Dromeosaur would try to keep its arms around the prey, to keep it disoriented and preventing it from escaping. Extant hawks and eagles also do this, it is called “mantling”, and is greatly helped by a “cloak” of feathers from the arms. Both adaptations are useful in themselves and at the same time it would be of great use for gliding and later flight. The grasping foot of the Dromeosaur would also be easily amended for perching.

All in all, a compelling and plausible explanation for the origin of wings and flapping behaviour in the whole Paraves clade.