That predatory dinosaur limbs acted much as described above has been known for some time. Life size dinosaur model More controversial has been the /ore and aft workings of their limbs. Part of the confusion stems from a misunderstanding of how the femur works in birds. Animatronic dinosaur Photos, film, and X-ray film of birds running slowly on trackways or treadmills show the femur nearly horizontal and moving only alittIe.22In mammals the femur is more vertical and swings through a strong propulsive arc. Since theropod hip joints are birdlike, not mammalian, it seemed that their femora might be horizontal and immobile too. But when looking at photos and films of ostriches running full tilt over the African flats-their wings held over their backs and exposing their knees to view-I saw, to my great surprise and delight, that the thighs were pumping back and forth much like those of horses and antelope. We have already seen that the muscles and joint surfaces of predaceous dinosaur hips allowed the femur to swing through such a wide arc, from about sixty degrees forward of perpendicular to the hips to a little past perpendicular to the hips.
Bird femora move so little at slow speeds because these tailless bipeds need to keep their knees as far forward as possible in order to hold their limbs under their body’s center of gravity. walking dinosaur costume The femur is so short that its non-use makes little difference at slow speeds. At high speeds the balance problem is not critical, while wasting a limb segment would be. Long-tailed theropods did not have the same balance problem, and the femora are so long that they must have been in full use at all speeds.