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re: T&F talks, SVP, Pteraichnus



David Peters (davidrpeters@earthlink.net) wrote:

<Generalizations are almost always bad.>

 Yes, in some regards. But I was making a general statement with respect
to my statements, clarified in the same paragraph. I have found that so
far, very few taxa exceed 45 degrees upward slope of the torso when the
given arm and leg lengths are used as walking aparatus. My arm
measurements start at the radius, and I draw the rest down through the arm
to the fourth metacarpal-phalangeal joint, which I raise just above the
ground (no tracks have yet to show it in regular locomotion). The humerus
is left as horizontal, so the glenoid height off the ground is almost
always the length of the forearm minus the wing digit, and with the digits
1-3 slightly elevating the arm up (as seen in tracks). The leg is measured
from femoral caput to ankle, which touches the ground (as shown in tracks
of pterodactyloids). In taxa for which a long fifth digit is known, I have
both alternately oriented the pes about 45 degrees up, or laid it flat,
but it doesn't change the length measurement by a significant degree
except in the basalmost known pterosaurs. Femoral lateral eversion also
affect leg length somewhat, and I try in most of my reconstructions to
articulate the femur with this eversion evident, so that would shorten the
leg by about 5% of the femoral length or so.

  So, in my work, I find that some taxa have extraordinarily long arms
relative to wings in the radio/metacarpal measurement, and some don't. And
there doesn't seem to be much of a phylogenetic signal: Taxa showing
nearly horizontal postures include *Beipiaopterus,* *Dimorphodon,*
*Eosipterus,* *Pterodactylus,* *Dorygnathus,* *Scaphognathus,*
*Austriadactylus,* *Dendrorhynchoides,* and I am betting one or two others
based on relatively good skeletons (including *Quetzalcoatlus* sp., but
this is based on Paul's skeleton and not my measuring). Taxa that incline
upwards of about 5-10 degrees include: *Anhanguera,* *Dsungaripterus,*
*Jeholopterus,* *Anurognathus* and a few more I'm sure. I found that
*Pterodaustro* as well as *Nyctosaurus,* incline at or above 45 degrees
(*Pteranodon* and *Nyctosaurus* share a nearly 60 degree angle). I looked
at *Gallodactylus*/*Cycnorhamphus* (the Quentstedt specimen), and it looks
like it may include up about 5 degrees or so, based on the arm to femur
morphology. Because of this, I can safely infer that more than half the
pterosaurs known were likely horizontal in orientation.

  The problem: I did these measurements from scaled figures I drew based
on measured specimens. Most specimens were measured by using photographs
and scaling everything exactly to the size I needed for the skeletal
reconstruction itself, rather than numbers in a book. So my estimates for
*Q.* sp. and *Pteranodon* are based off Paul's reconstruction, the latter
being a composite, but there are specimens with both arms and legs so I am
confident it's accurate; and the latter based on a single specimen
according to Paul. I have the cranial quetz paper, not the postcranial
one, so that would have to do for now.

  This is why I generalized.

<Specific matching of prints with printmakers is almost always good. When
you do match print to printmaker and you find a horizontal backbone, let
me know.>

  Horizontal backbones, see above.

  Matching sub-phalangeal cushions: tricker if you're a lizard and a
mammal, seems fairly secure in birds with the typical pedal formula
represented as pads in some, but not all, species. Some species, I think,
do merge pads, and Emma Rainforth (2003, in _Palaeontology 46(4)) showed
that inter-phalangeal joints of various prosauropods don't always
correspond to tracks normally considered to be theirs by relationship of
digit orientation, extent, arrangement, phalangeal divisions, etc., even
when in the same formation. Other research from Rainforth (including her
MSc thesis, 1997) shows similar conditions in bird tracks. So a reasonable
course of action in applying track maker and track is to find vertebrate
fossils of the applied taxon in relation to the tracks, as well as
determining how much variation in phalangeal pad position there is and its
correspondence with the interphalangeal joints. In some pterosaurs the the
two medial phalanges of the fourth digit are so small, they may likely
just form a single pad for all effective purposes, and the four joints of
the third digit with a tiny median phalanx could possibly sport just ONE
pad instead of two, because of the size of the digit.

  Cheers,

=====
Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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