A note added November 12, 2020
Quetzalcoatlus was flightless due to clipped wings (vestigial distal wing phalanges). Here is the link on that data.
As a Guide to Artists and Modelmakers
Many artists add pterosaurs to their illustrations and many model makers have been assigned the task of reconstructing flying pterosaur skeletons for museums. This blog is here to provide some heretical suggestions that, doggone it, make more sense all the way around!
Properly Configuring Quetzalcoatlus in Flight – The Knees
It is a common tradition to extend the hind limbs behind flying pterosaurs and, judging by the full-scale model at the Texas Memorial Museum (TMM, Fig. 1), this practice also extends to the largest of them all, Quetzalcoatlus. Imagine the mechanical strain at the ball joint of that extended femur! Unfortunately that configuration also assumes a dinosaur-like right angle femur for Quetzalcoatlus, something only basal pterosaurs had. Q and its sisters had sprawling, lizard-like hind limbs, yet still able to place the feet beneath the torso as blogged earlier, and as shown here. Plus, extending the legs posteriorly gives the uropatagia (preserved not on Q but on other pterosaurs) nothing to do. Finally, the large thigh muscles originating from the anterior ilium would have been overextended if the leg was posteriorly oriented.
Much better to extend the sprawling femur in a sprawl: laterally with the knees not drooping too much. Then extend the tibia in the same plane. This gives Q a horizontal stabilizer (Fig. 1), like an airplane and echoes the hind limbs of Sharovipteryx, a pterosaur forebearer. In flight, the legs would have provided their own lift in this configuration, without additional strain on the hips to hold them up in the airstream.
Properly Configuring Quetzalcoatlus in Flight – The Feet
In the TMM model the soles of the feet are pointing to the sky. This give the feet nothing to do but dangle. However, with the knees and shins out, the soles point medially, back to the tail root between them. Spreading the toes allows the skin between them (preserved on other pterosaur specimens) to form aerodynamic surfaces to create lift. In this case the lift would be lateral, which pulls the feet out laterally, which helps the knees to stay extended with less effort, again, as in Sharovipteryx.
Properly Configuring Quetzalcoatlus in Flight – The Elbows
It’s traditional to extend the elbows straight out from the chest laterally, then extend the wrist straight out from the elbow. In birds and bats this would be considered over-extension. In Q let’s move the elbows back to where birds and bats put them and let’s raise the elbows slightly to provide the wing some curvature. Everyone knows a wing should be curved. Funny how few pterosaur artists add this subtle but vital element.
Properly Configuring Quetzalcoatlus in Flight – The Wing Finger
The model makers of Q. correctly included a substantial angle between metacarpal 4 and digit 4, following a natural stop in the specimen. This is different than in other pterosaurs, like Anurognathus and Nyctosaurus, in which the fully extended wing finger virtually lines up with the fourth metacarpal. This gives the Q wing a deeper chord at the base of the flight finger. This depth may be related to the brevity of phalanx 4 giving Q more of a duck wing, than an albatross wing.
Properly Configuring Quetzalcoatlus in Flight – The Neck
The TMM model makers extended the neck in their full-scale Q about as far as it could go. However, soft-tissue fossil evidence (Frey and Martill 1998) in Pterodactylus indicates that the longer necks were supported by a tall, narrow, muscle and tendon complex that spanned across the arc of a ventrally convex cervical series. So such a neck curve is integral.
Properly Configuring Quetzalcoatlus in Flight – The Head
No doubt Q could have moved its head anywhere it wanted to, but the standard flight position would have been “nose down” as reported (Witmer et al. 2003) in other long rostrum pterosaurs, like Anhanguera. It’s not that the back of the head drooped down. It was the front that did.
I Haven’t Yet Mentioned the Wing Membranes
But notice how nicely this configuration works with an independent hind limb not encumbered by the deep-chord wing membrane that is the modern paradigm. Read more about wing membranes here.
The flying Q. model of Paul MacCready had the hind limbs tucked in, like a bird, following Kevin Padian’s reconstruction of the early ’80s. The model flew just fine. However with a sprawling femoral head, such a configuration would have been a strain on the animal and therefore highly unlikely. No one illustrates that configuration today.
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.
Frey E and Martill DM 1998. Stissue preservation in a specimen of Pterodactylus kochi (Wagner) from the Upper Jurassic of Germany. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 210: 421–441.
Witmer LM, Chatterjee S, Fransoza J and Rowe T 2003. Neuroanatomy of flying reptiles and implications for flight, posture and behaviour. Nature 425:950-953. online pdf
Flying Pterosaur Model of Paul MacCready online pdf