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Re: Hone and Benton 2007 (their second paper)



Michael Habib wrote:

That's quite intriguing; thanks for posting on it (I must have missed that presentation >somehow...I'll have to look up Atreyee's thesis). In any case, the predation mechanic sounds like
a strong conclusion to me (for what that's worth). However, I have a feeling that concluding bipedal locomotion from those claw morphologies is slightly premature (though certainly among the range of rational conclusions).

Having not seen the presentation either, or read the entire thesis, I don't know how strongly held that conclusion (bipedal walking) was. The hand-held predation hypothesis is certainly appealing: fish can be slippery!


In many taxa, much of the weight would not be put on the actual fingers during quadrapedal locomotion (metacarpal IV would be the main support). In those that would use the manual digits I, II, and III when walking, I would not really expect the claw shape to be under particularly strong selection from a locomotor standpoint, because the forces would still be largely transmitted to mtC IV.

Yes, that makes perfect sense.

If the claws were used in feeding, that signal would (I hypothesize) be likely to swamp any weak locomotor selection on claw shape.

Exactly. Predatory birds (raptors) can walk on the ground quite comfortably, even though their claws are specialized for predation.


Besides, the manual claw function in locomotion w
ould largely have been to grip during leaping launch, in which case an "arboreal" like claw might actually be the most mechanically sound solution (making it doubly useful).

So what would the manual claws actually be gripping during a launch?

Also an excellent point. After all, the hind limbs in pterosaurs aren't really that weak, relative to their mass (and relative to the size of the thorax and/or abdomen). Really, pterosaurs' startling >proportions are a result of hypertrophy of the forelimbs, head, and neck. As such, I do not see >any reason why a pterosaur could not walk and eat, or move bipedally to reach for an object with the forelimbs. However, running and launching would be much better served (ie. much more
powerful) using quadrapedal progression. Combining this fact with the known quadrapedal trackways, and the fact that all known pterosaurs could contact the substrate with the forelimbs >while standing, I suggest that the most rigorous actions (sprints, launches, etc) were accomplished quadrapedally. Basic walking probably was, as well, barring munching on the move.

Agreed. I guess the 'take-home' message is that, when it comes to non-aerial functions (terrestrial locomotion, feeding, mating, etc) the forelimbs and hindlimbs were employed opportunistically. It probably also varied between different pterosaurian taxa and/or with ontogeny. But for rapid progression on the ground (or as 'rapid' as a pterosaur could get) quadrupedality was probably the general rule.


Cheers

Tim

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