Tuesday, April 08, 2008

Raeticodactlyus = Fishing Eagle?

Without giving entirely too much away, I'm preparing a largish post about the new pterosaur, Raeticodactylus filisurensis, and that post includes an attempted life restoration. I have, as usual, run into a snag. What we have here is a rhamphorhynchoid pterosaur which seems close to Eudimorphodon and Austriadactylus, but has different limb proportions (longer), a very unique skull shape, and...most problematic for me, parasagittal hind limbs. Or so they seem. No pelves were found, so the acetabular angle is unknown. The femur, however, has a distinctly perpendicular head (like dinosaurs), which implies that the hindlimbs were directed underneath the body.

Problem? Well, every other rhamphorhynchoid pterosaur had sprawling or semi-sprawling hindlimbs, and those hindlimbs were thusly incorporated into the wing surface. Because the femoral socket was on the same general plane as the humerus socket, the legs could be moved up and down with the flapping action of the arms. But if you throw me a rhamphorhynchoid pterosaur with parasagittal hindlimbs, the picture blurs.

Remember when Microraptor was found and initially restored in a sort of flying squirrel pose? We know such a posture would be impossible for the hindlimbs to take--the femora would dislocate. That's the problem facing Raeticodactylus if it had a parasagittal posture against a sprawling (flying) posture for the forelimbs. So what do I do? Clearly, the hindlimbs must not have been attached directly to the cheiropatagia. Stecher suggests that Raeticodactylus was a fish-eater (and/or shellfish eater), so perhaps...

Perhaps it used its parasagittal, unladen hindlimbs to grab fish out of the water, like eagles do! If that's the case, then the cheiropatagium must have terminated caudally to the pelvis. Stecher also suggests that Raeticodactylus had a typical "hook" toe like other rhamphorhynchoids, but figuring out that problem will be far easier than this one was.

UPDATE: Dave Hone has shot the fishing-grabbing idea down, for the simple reason that pterosaurs weren't doing a lot of grasping with their feet. I still wonder about how the patagium attached to a parasagittal leg, though.


Alkalynic said...

Raeticodactylus is not the only pterosaur with a perpendicular femoral head. :-)

It is disappointingly not as 'theropod-like' as first described. :-(

Zach Miller said...

MEH! So it's not as close to the ptero-urvogal as first glance might suggest, huh?


Back to square 1!

Alkalynic said...

Even at first glance, it is very similar to the other multicusped pterosaurs. It is still very basal and it shows that pterosaurs were doing very weird things. :-)

For something closer to the root, there's a certain dissertation that someone should publish about two Texan archosaurs. >-(