A Closer Look at the “Catapult Mechanism” in Pterosaurs

There seems to be a continuing interest in the pterosaur wing launch hypothesis championed by Mike Habib. It’s a weekly favorite. Here’s another illustration (Fig. 1) that should clarify certain problems found in the Habib/Molnar concept. Mike and I have talked about this at length with no movement on either side.

The so-called catapult mechanism in pterosaurs

Figure 1. Left: The so-called catapult mechanism in pterosaurs. Right. The actual design of pterosaur hand (in this case Anhanguera/Santandactylus). Click to enlarge. Note there can be no pinching of the extensor tendon beneath the weight of the pterosaur for the reasons illustrated here and explained in the text. The metacarpals were not configured on the dorsal (in flight) or lateral (on the ground) side of metacarpal 4 in ANY pterosaur specimen. They were anterior whether your follow Bennett's (2008) stacked metatarsal interpretation or mine (links in text).

In Science it is Important to Expose Errors 
And that’s why in every blog I encourage those who have updated data to alert me to errors that I produce. In this case a reconstruction and a hypothesis promoted on pterosaur.net are reexamined and challenged.

Forewing Launch and the Catapult Mechanism
Dr. Mike Habib (2008) proposed a fore wing launch method for pterosaur take-off which was illustrated by artist Julia Molnar online (and see above, left). A catapult mechanism (as in grasshopper hind legs) was specified to increase the power of the launch. Unfortunately the illustration by Molnar (Fig. 1) includes several errors which preclude the possibility of a catapult mechanism in pterosaurs.

Molnar illustrated metacarpals 1-3 way too short. On the right the correct length is indicated. All four metacarpals were actually the same length. That means fingers 1-3 extended beyond the metacarpus. Pterosaur manus ichnites only impress digits 1-3. No trace of digit 4 ever impressed. Thus there was no pinching of the extensor tendon beneath the weight of the pterosaur to load the catapult prior to launching.

Furthermore, as in lizards, the long metacarpal extensor actually split prior to the knuckles to insert on the medial and lateral sides of the proximal phalanges. They did not extend over the knuckle. Much smaller muscles and tendons, the digit extensors (see above and here) extended over the knuckles.

Finally the flexors had to insert further distally than Molnar illustrates. In the Molnar illustration the flexors reach the limit of their ability to flex at 90 degrees. By inserting the tendon further distally flexion can continue until the wing finger is completely folded (see sequence here). More on pterosaur wing evolution here. More on the placement of pterosaur metacarpals here.

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.

References
Bennett SC 2008. Morphological evolution of the forelimb of pterosaurs: myology and function. Pp. 127–141 in E Buffetaut and DWE Hone eds., Flugsaurier: pterosaur papers in honour of Peter Wellnhofer. Zitteliana, B28.
Habib M 2008. Comparative evidence for quadrupedal launch in pterosaurs. Pp. 161-168 in Buffetaut E, and DWE Hone, eds. Wellnhofer Pterosaur Meeting: Zitteliana B28

Pterosaur.net/anatomy

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