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Re: How did dromaeosaurs use their arms?

Dinogeorge writes:

When I walk down the street and want to turn left, I do this by moving my
feet against the ground, not by flailing my arms against the air. All
tetrapods that I have ever observed, small and large, from kangaroo rats to
kangaroos, including birds, do likewise.

Sure. But the arms, even in a biped animal, help to balance the body during locomotion and can assist in turning, changing direction, etc.

Surely pelage, feathers, whathaveyou, help terrestrial animals as far as insulation goes. As far as feathers on the arm, dinosaurs have a femoral head that is cylindrical (unlike mammals where it is spherical) and allows little abduction/adduction. They therefore have a stiff-action limb that is great for walking/running forward in a straight line, but is less great for tight turns just because of the physical geometry of the hip socket and femoral head. Feathers on the arms, as well as a long, stiff tail, may have allowed a terrestrial predator with less mobility in its hips to compensate for this by incorporating the forelimbs and tail in turning, etc. And then there is always sexual display, etc.

As far as streamlining from feathers, penguins are aquatic birds that use the feathers on their bodies to swim more efficiently through the water.

So the presence of feathers on an animal does not necessarily have to reflect an arboreal ancestry and could be used for other purposes as well. The complexity of the maniraptoran fossil record that is unfolding before us makes it difficult at this time to conclude whether maniraptorans are descendants of arboreal animals or terrestrial ones. In either case, the presence of feathers on the forelimb does not necessarily preclude a terrestrial ancestor and there are other viable scenarios.

Matt Bonnan
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