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Re: Longisquama



In my last post the vertebral series was undiscovered. Now it is found
and the reconstruction is complete. A few notes:

As in Sharovipteryx, there is no way that Longisquama was a quadruped.
The hind limb is twice the length of the forelimb, which due to toro
length and elevation, barely reached the level of the knee when bipedal.
The torso is also long with a center of balance just anterior to the
ilium, far from the humeral glenoid. So, with two pterosaur sister taxa
now obligate bipeds the case is strengthened that basal pterosaurs were
also bipeds. Which is why, IMHO, with freed up fore limbs, they were
able to transform them into wings. And?the wings came last. That they
maintained their quadrupedal abilities probably has more to do with
arboreal clinging using all fours, than with terrestrial progression.
Doesn't that make sense?

The sacral series is dorsally concave, matching the curve of the ilium.
At least five sacrals are present. The caudal series is no longer than
the longest plume and is tipped with the tuft of hairs seen on other
prolacertiforms including anurognathids. Hyper-elongated caudals, as in
pterosaurs and Sharovipteryx are present together with a single parallel
hemal matching each centrum counterpart in length, as in Sharovipteryx.

The metatarsals are less than subequal. The series is slightly shorter
medially than laterally. Likewise the phalanges increase in length
laterally (sorry mixed up a few digits yesterday--they're bundled with
one and two on top of three and four). As in Sharovipteryx and basal
pteros, phalanx 5.1 extends beyond metarsal IV, but unlike pteros it
extends anteriorly. Evidently, as I guessed earlier, the hyper-flexed
pedal digit V in pterosaurs is an arboreal adaptation for perching
because it enables the pes to be used like a universal wrench. The
posterior prop (= rocking chair) hypothesis may still have some
validity, because certain Rotodactylus tracks indicate a hyper-flexed
pedal digit V yet still have the capability of quadrupedal progression
with a typical if rather small manus, as in Cosesaurus. The prop is not
used by Sharovipteryx or Longisquama.

The extended post-elbow dorsal series may be the best clue as to why
only the anterior of Longisquama was  the only portion known for so
long. Anteriorly the dorsals are closely spaced and buttress each other
against taphonomic influences. Posteriorly the dorsals are not so well
protected and so ended up in a long sinuous lineup while the sternal
complex was washed anteriorly, the pelves were flipped over and the hind
limbs were turned upside down.

Also, I'll bet no one ever scanned and mouse traced this specimen
before. Some things _are_ visible on the screen that escape the eye and
microscope. It's not so much a matter of seeing, but of recognizing --
and I didn't recognize the vertebral series until I started coloring in
the possible elements and notin that they lined up like box cars.

I find it interesting that the tail does not extend off the plate, but
curves along the edge to stay on the plate. Likewise, the plumes seem to
fill the plate to its edges.

Could find no postive trace of uropatagia. Disappointed. With the hind
limbs upside down, any possible membranes would have been on top of the
forelimb and ribs. Some interesting filaments do appear to emanate from
the posterior of the forelimbs, but a minute later I noticed that these
same filaments seem to continue anteriorly, so they may be not of this
animal.

Wonder if the plumes were colored to match the greenery or to stand out
against it? The whole animal when resting would have been only the size
of a clump of grass.

More later,

By the way, did I mention that Tanystropheus is similarly adorned? That
must have been a sight!

David Peters
St. Louis