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Re: four-winged dino -- ptero homology?



    Ray Stanford wrote:
    David Peters said:

>Pterosaurs...apparently ran bipedally on
>hind limbs encumbered(?) by flight membranes..." <

    Without a stitch of trackway evidence to back up such a statement,
shouldn't use of the word "apparently" (as applied to bipedal
locomotion) be
taken with a very substantial 'grain of salt'?


Ray, I know of trackways belonging to ctenochasmatids, pterodactylids,
gallodactylids, anhanguerids, and azhdarchids. All are quadrupedal, and
plantigrade as they should be judging from pedal morphology, manus
morphology, and relative forelimb length. What we don't know of
trackways include all the rest of the pterosaurs, from Triassic basal
forms to nyctosaurids, all of which were also capable of quadrupedal
progression!

Now that I've successfully shot myself in the metaphorical foot, let me
remind you of the (now cliché) 19 living lizards which are also
quadrupedal and plantigrade, yet capable of morphing into bipedal,
digitigrade, narrow-track sprinters at the drop of a hat.

Pterosaurs have all the characters that separate these "bipedal" lizards
from the strictly quadrupedal ones -- and in each case have exagerated
these features: 1) relatively short, non-undulating torso; 2) relatively
elongated cervicals; 3) reduced and proximalized transverse processes
and hemal arches; 4) elongated anterior process of the ilium; 5)
expanded and fused sacrals (and increased sacral count in pterosaurs) to
name the most important.

Plus, we have trackways (Rotodactylus) that match the pedal morphology
of pterosaur sister taxa Cosesaurus and Langobardisaurus that are narrow
gauge, digitigrade and _occassionally_ bipedal. Plus we have
Sharovipteryx, perhaps the closest sister taxon to pterosaurs, which is
an _obligate_ biped.

You may never find trackway evidence for bipedal pterosaurs because when
pterosaurs move slowly, as in beach-wading and feeding, they tend to put
all four limbs down. Trackways tell that story. Morphology and phylogeny
tells what pterosaurs were capable of.

Hello, Dr. Beebe!

More later,
David Peters