Just how much muscle surrounded those skinny little hind leg bones on pterosaurs? Hind legs are basically an afterthought in the illustrations of many paleo-workers and artists, but pterosaurs give us four points on the anatomy to figure the proximal musculature (see below).
The anterior and the posterior tips of the ilium provide the first two of these points. As in lizards, crocs and birds, these points determine the fore/aft distance of the thigh musculature. In front the depth of the thigh musculature is determined by the prepubis, which in some pterosaurs is relatively short. In others, like Rhamphorhynchus the prepubis can extend beyond the knee. In back the depth of the thigh musculature is determined by the tip of the ischium, which can also be relatively deep or shallow.
Let’s take a look at a few examples of birds to start:
Bird thighs, no matter what type of bird they appear on, bend the knee with anchors along the length of the ilium. Here you can see that bird thighs extend for about half the length of the torso in birds.
Early pterosaurs had a thigh that was less than half of the torso, but much longer due to a longer femur. This is trait that originated in Sharovipteryx and Longisquama, the (hind-limb) leaping fenestrasaurs. Later pterosaurs shortened the dorsal portion of the torso so that the length of the ilium became half the torso length. Only in the flightless pterosaur, SoS2428 does the ilium extend for more than half the torso.
Okay, so artists, we need to add some meat to those pterosaur thighs. Here is an example of a Content Paradise Zhenyuanopterus with thighs that are too small (you can’t count the uropatagia there!), but I love the narrow chord sailplane-like wing configuration.
Finally, I can’t let the size of those thighs go by without bringing attention to home much MORE thigh muscle is present than forelimb muscle in many pterosaurs. Sure the femur is narrower than the humerus, but really, it’s the muscles and their leverage that drive leaping, not the bones.
As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.
Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.