[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Let's find the basal Ornithodire - part 2
... and now for part two ...
<DP: Whoa! Where did this come from?? They hold their arms like
gunslingers do. Or like bipedal lizards do. Or like birds and bats do.>
Hmm ... I was referring to quadrupedal stance. Birds do NOT use their
arms in the same manner I described, nor in the "gunslinger" pose Dave
mentions, and to my knowledge, bats in a quadrupedal walk have the humerus
at about 45 degrees outward from the parasagittal.
<do you mean laterally (while standing)? or dorsally (while flying)?>
<DP: Inboard, you mean proximally? Proximal of the ulna? A little confused
by terminology here.>
Inboard I mean by along the caudal margin of the ulna when the
radioulnar unit is horizontal and outstretched, as the pterosaur would be
when flying. The carpus acts in the same orientation during quadrupedal
posture (as in Kellner/Wellnhofer's drawing of a quadrupedal
<DP: True. But then, all I'm looking for is a longer fourth than third.
Impossible to find in Archosauriformes and especially Archosaurs. That's a
Not impossible, just unlikely. We have not found such an archosaur, but
this does not mean one does not exists.
<Someone had to be first. I have been very open and public about what to
look for and where to find it (pterosaurinfo.com). No one is currently
working on this problem as far as I know. No one has disputed or come up
with a more precise tracing. Again, both are difficult, otherwise they
would have been found before.>
Bennett has, as I am now, disputed this method, that being specifically
on the skull of *Anurognathus,* which shows VERY visible elements, series
of preserved areas, and preparation artifacts in tool scratches, etc. This
refutation will not occur in print until the method is described in detail
in print, with step by step examples, which I suggest you do to ligitimize
the method and allow it to be tested. Then, practice your methods TO THE
LETTER as described, unless you then change it, and make note of exactly
what settings, tools, numbers, etc., were used to derive the traceable
image, and the method by determining, objectively, how to find such
ephemeral traces. Others have suggested blind tests and means to reconcile
issues of others not finding the material, but I have not seen results of
these in agreement with Dave, at least as reported.
<I'd be glad to review your Sharovipteryx tracings. Maybe you found
something I missed.>
I'd have to get a VERY detailed photo of this material, for such a
I have made a tracing of a very complex crushed skull with masses of
unidentifiable yet discolored material identified as cranial in
*Protarchaeopteryx*, marking slab cracks, "escarpments," foramina, bone,
and dentition. My tracing, which includes a layer of the tracing, the bone
itself, and my verbal description of the "key" to the lines I use to mark
bone, impression, etc., is available at request. Mickey Mortimer has done
a similar technique, and both of our works are largely concordant with one
another. I did NOT use his layer as a source for mine, and we were
independant on this matter. I learned of him making his tracing before I
prepped mine, but did not see his till after mine was completed. Thus, it
operated as a blind test. We DID differ in how we identified some of the
same features, however, but that's become universally understood in this
forum, I think. ;) But, I bring up *Protarchaeopteryx* because this was
based on a VERY large photo (made by an analogue light-exposure camera,
not digital) of a single small region of the slab, 1867x1468 in size. A
similarly defined, but not equal in size or proportion, photo would be
preferred if such exists, so that the issue of pixellation (brought up by
many others as well as Bennett) does not become a problem.
<Not sure that I remember this or espouse it now. In flight I do suggest
that the humeri were held about 40- 55º from the sagittal plane, a little
closer than others suggest (pterosaurinfo.com).>
This refers to Dave's illustrations of skeletons standing on two legs
with the humeri held parallel to the spines.
<Again, I'm not aware of any published, web or print, dorsal views that
you're referring to.>
See above. The humerus is shown at length in the illustrations. If this
was done to "save space," I can understand, or provide an adequate scaling
mechanism for the obersver, I can also understand, and should have asked
for a clarification.
<The great thing about the new technique is that in messy cases like
Longisquama, the various visual layers one can construct can help visually
segregate this from that. The irregular and massive portion you refer to
Ah. On a tangent, a question to Dave: how did you deliminate the margin
between the lachrymal and frontal/prefrontal complex, and not idenfify a
postfrontal, on the *Tanystropheus* skull that appears at
http:www.pterosaurinfo.com? (The dorsal cranium shows innumerable
fractures and cracks in the mineralized bone that in the photo appears to
obscure finding margins of a lot of bones in this.)
<Tell me more. I can't imagine how, but I'm willing to learn.>
I wrote previously at http://dml.cmnh.org/2004Sep/msg00458.html:
"However, the more critical issue, and which has eluded paleontology --
and even Dave's techniques and researches -- has been a "pro-pterosaur"
that shows a long arm with modifications towards flight, as in
broadening of the sternum, formation of a keel, elongation of the arm,
solidification and expansion of the sacrum, "locking" of the dorsal
spine, closure of carpal contacts into sutures or fusing of the
elements, reduction of the proximal metacarpals (I-III) relative to the
fourth, elongation of the fourth metacarpal and digit, lateral rotation
of the scapulocoracoid and thereby also the humeral glenoid...."
*Confuciusornis* shows all these features save those I listed that are
clearly only present in pterosaurs, the last three:
"...reduction of the proximal metacarpals (I-III) relative to the
elongation of the fourth metacarpal and digit, lateral rotation of the
scapulocoracoid and thereby also the humeral glenoid...."
6 out of 9, a 1:1.5 ratio, so pretty good, eh? No protorosaur shows
these many supportive features.
Okay, just to show how much I am NOT against prolacertiform ancestry,
note that I am FULLY aware of the fossil record and being incomplete, so
the possibility of such an ancestral series as we see for birds among
dinosaurs for pterosaurs themselves is still likely.
<DP: Why are you ignoring Peters 2000 and 2001? I found four.>
Dave's "proto-pterosaurs" show only "ephemeral" features that make them
so pterosaur-like. Others who study these animals, including Renesto,
Wild, Rieppel, Li, et al., have not corroborated these to my knowledge.
These four organisms do not, in my opinion, have as close to the
"proto-bird" situation in bird ancestry as coelophysids have to
ornithuromorph birds. And coelophysids even have furculae (they have five
metacarpals, open sutures in tarsals with two sets of "locked" carpals, a
short arm compared to leg and dorsum, a flexible dorsum, an elongated
ilium, expanded sacrum compared to THEIR ancestors, and so forth, present
in birds, but the intervening taxa, even the HUGE ones like *Allosaurus,*
share MORE features with birds). In the series, Dave has not found this
critical "proto-bird," the "*Archaeopteryx*" or the "dromaeosaur" of
prolacertiforms. Instead, Dave offers that his ephemeral identifications
approximate these, thus placing these taxa "closer" than any one else has
agreed they are by looking at the same material. The difference? Dave's
<At present it is the only tool we know that takes the bias out (as much
as that is possible), perhaps not when it is originally constructed by the
biased scientist who built it, but it can bias can easily be dissected
from it via review by others.>
Cladistic algorithm crunchers, e.g. PAUP*, MacClade and ilk, do NOT take
bias out. They use mechanisms like likelihood analysis and parsimony to
find short trees and the least reversals possible in a tree. Bias still
exists in what taxa are included, how they are coded, the proportion of
coded taxa to characters, etc. David Marjanovic has talked about this to
<They why didn't Unwin and Kellner get more resolution out of their trees?
They didn't get the result they wanted.>
Because they weren't trying to get A result, they were looking to see
the result of the taxa and characters included. There was no "azhdarchoid"
clade being MADE, nor was there an "ornithocheiroid" or "pteranodontoid"
clade being made, but rather they included characters they felt should be
in the matrix, and the taxa, and they published the result. This is how
they SHOULD have done it.
<DP: I would expect the same. Juveniles should group with adults.>
But they don't. An example may be found in the Bakker, Williams and
Currie analysis of 1988 showed a skull of a small tyrannosaur, now
*Nanotyrannus,* to be clade along with "albertosaurines," despite being
almost universally accepted as a juvenile *Tyrannosaurus.* Examples exist
among the salamanders (best explified among, I should say) -- this tidbit
comes from digimorph (on a quick search, I have not the time to dig
through my boxed up papers ... I'm moving to Portland in a few days):
"*Eurycea waterlooensis* was described by Hillis et al. (2001), and the
specimen featured here is a paratype. It is most closely related to *E.
robusta,* the Blanco blind salamander, and *E. rathbuni,* the Texas
blind salamander. It differs from other species of *Eurycea* in the
following combination of external features: perennibranchiate; external
eyes absent; 12 costal grooves; limbs proportionately short; and tail
fins weakly developed."
The traits listed are larval in nature, and found in basal salamanders,
for example the sirenids. References include:
Chippindale, P. T., A. H. Price, J. J. Wiens, and D. M. Hillis. 2000.
Phylogenetic relationships and systematic revision of central Texas
hemidactyliine plethodontid salamanders. Herpetological Monographs
Hillis, D. M., D. A. Chamberlain, T. P. Wilcox, and P. T. Chippindale.
2001. A new species of subterranean blind salamander (Plethodontidae:
Hemidactyliini: Eurycea: Typhlomolge) from Austin, Texas, and a
systematic revision of central Texas paedomorphic salamanders.
Mitchell, R. W., and J. R. Reddell. 1965. Eurycea tridentifera, a new
species of troglobitic salamander from Texas and a reclassification of
Typhlomolge rathbuni. Texas Journal of Science 23:343-362.
Potter, F. E., and S. S. Sweet. 1981. Generic boundaries in Texas cave
salamanders, and a redescription of Typhlomolge robusta (Amphibia:
Plethodontidae). Copeia 1981:64-75.
I suggest expanding the work of Wilcox and Hillis, among the others, as
most of my found references on the subject of neoteny and paedomorphism in
salamanders derive from their work. How easy is it to ascribe a juvenile
of a species as an adult of a more primitive taxon? I'd say very easy. As
an adult of a more advanced taxon, not so easy, but still possible. I
suggest taking the ID of adulthood without corroboration with a hefty
handful of salt (kosher if anyone prefers).
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)
Do you Yahoo!?
New and Improved Yahoo! Mail - Send 10MB messages!