Re: pteros have lift-off

[Michael Habib <mhabib5@jhmi.edu>]

David Peters wrote:

> Mike, Let's go, waaay back, to the origin of pterosaurs. Mike, where 
> do pterosaurs come from? And which one is the most basal known 
> pterosaur?

You know even better than I do that the answers to those questions are 
quite contentious.  In any case, looking at all of the available trees, 
the immediate outgroup might be bipedal or quadrupedal.  I'm not in a 
position to say with any certainty what the most basal known pterosaur 
is, but I can say that for a robust ancestral reconstruction (something 
I used to do a fair bit) we'd really want several basal pterosaurs (not 
just the most basal in a particular topology).  But, regardless, I 
understand the point your making, which brings us to:

>  What do these taxa have to tell us about a quad launch vs. a biped 
> launch? Short explanation will suffice (aka: big arms, big hips, 
> whathaveyou).

They probably don't tell us very much about launch in most of the 
clade, but they can give some idea of where the launch kinematic 
started.  Most of the relatively basal taxa seem to be built more for 
quad launch (robust humeri, deflected dp crest, etc) but being 
reasonably small in most cases, they could get away with either mode 
(albeit slower launch with biped leaping).  I know that many of basal 
forms also have large hips (though they nearly all seem to have rather 
more powerful forelimbs), and I am aware that you recover bipedal 
outgroups to the base of Pterosauria.  If this is correct, then quad 
launching probably originated early in Pterosauria, but after the base 
node for the group.  But now we're talking about the origins of the 
primary pterosaur launch mode - this is a very interesting question, 
but different from the one that I've been asking, which is "how did 
most pterosaurs launch?".

> Also, which is the most important articulation creating the most 
> forelimb launch power? The humerus/antebrachium? humerus/shoulder? 
> antebrachium/metatacarpus? Or all three?

Most of the power, strictly speaking, comes from muscles that cross the 
shoulder and elbow.  The metacarpus adds significant excursion length, 
especially during the vault phase, however.  Are you using the term 
power in its technical sense, or in a general "where does the speed 
come from" manner?

> Finally, in present day leapers, from frogs to kangaroos, sort of 'Z' 
> fold gets created by the femur, tibia and tarsal/pedal elements. And 
> lots of final push comes from the large pedal digits. Is there a 
> z-fold analogy in the forelimb of pterosaurs. And is there lots of 
> push coming from the manual digits? At present, I don't see either.

There is sufficient flexion in forelimb joints to give the release 
distance and power required; at least everything I've worked up thus 
far points in that direction.  If someone can show mechanical evidence 
to refute it, then I'm all ears.  Manual digits don't add power in the 
normal way, but there is an energy-storage system in the long tendons 
of the wing finger.  They unload of this stored energy is unusual for a 
tetrapod, granted, but would be a very powerful catapault mechanism.  
Note that many ungulates are accomplished leapers and do not have long 
pedal digits that unload in a roll phase (as seen in frogs et al).

> BTW, I'm not arguing a particular point. I just want to understand in 
> lieu of measureable images and diagrams of a leaping pterosaur, which 
> seem to be lacking.

No problem; I understand.  Though I am curious as to what you plan to 
measure from the diagrams - aside from showing the proposed kinematic, 
most of the relevant numbers (structural strength, power output, etc) 
won't be measurable from an image.  Are you just referring to wing 
clearance?

Cheers,

--Mike


Michael Habib, M.S.
PhD. Candidate
Center for Functional Anatomy and Evolution
Johns Hopkins School of Medicine
1830 E. Monument Street
Baltimore, MD 21205
(443) 280 0181
habib@jhmi.edu