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re: Jaime's ptero comments
Dave Peters <davidrpeters@earthlink.net> wrote:
<I'm not saying that the new found creature is not a pterosaur. It is one.
And I'm not saying it's not an egg. I believe it to be so. Scratch your
heads for awhile and come up with another possibility. I have, and the
bones are confirming it.>
Then the suggestion would be this is an adult and the LARGE chunks of
eggshell around it in it's periphery would be reference to the cracked
eggs of other animals, perhaps not pterosaurs.
<Regarding juvenile cartilage vs. bone: in the little reading I've done on
pterosaur histology one point is made by the authors and that is pterosaur
bone develops differently than that of any other vertebrate. The details
are in the literature. What is happening in the juvies I cannot say, but
apparently it is not quite like that of any other diapsid clade.>
But similar perhaps to non-diapsids? The argument of "unlike other
diapsids" being an allusion that can make the animal form bone material
from the osteoblasts in the cartilage skeleton AFTER hatching is hardly
parsimonious. Similarly, pterosaur growth was different, indeed, from that
of birds and mammals, but hardly so out of the ordinary as to suggest that
it, unlike any other amniote, could not form bone prior to maturization.
In fact, ALL amniotes derived the calcium for their bones in only two
ways, and this is true for all viviparous animals as well as oviviviparous
and oviparous animals: calcium is either derived from the decaying bone of
the mother, or from the shell of the egg, as the foetus developes. By the
time the foetus is ready to emerge from the egg or womb, this animal
should have all of its vertebral centra, most of its limbs, and all other
endochondral bone as ossified to most extents. This leaves only the dermal
and epipophyseal portions of the skeleton to ossify, for the simple reason
that this is where 50% of the growth of the limb occurs during
matriazation. This pattern of growth, with replacement of cartilage during
growth, is found in sharks, as well. Pterosaurs should be considered to
have such a growth development system regardless of "birth" or "hatching"
a priori to any arguments that this was not so.
Arguments that this embryo was NOT an embryo depend on matters of
maturization of bone, epipophyseal development, fusion of sutures, and the
lack fo adult traits that cannot be explained as paedomorphic. In the case
of paedomorphosis, this must be shown to develop from a series in one way
or another, including comparison to another series. One cannot just say
that any juvenile features would therefore be paedomorphic as an excuse to
bat away a contradicting thoery: this is not positive evidence.
So far, NO one has corroborated, looking at the same photos and slabs as
Dave has, the existence of these juveniles. In most cases, these appear as
natural effects of multi-colored ash (as in Liaoning/Liaoxi beds and at
Daohugao), pedestalling of the matrix during splitting (as occurs
frequently in the Solnhofen material), preparation artifacts (the entire
preserved surfaces of the KJ1 and KJ2 slabs are wholly unnatural, being
remnants of preparation providing that the material encased in the hard
chalk was "raised" up and that more material was not found below the
bedding plane), or via taphonomic effects (as in displaced carbonaceous
material, shattered then scattered bone, displacement, etc.) that are then
interpreted as parts of a different animal. This is why personal
examination, CT or X-ray study, and weeks to months of double-checking
tend to occur before any specimen sees print. I am told that Mark Norell
and Xu Xing have material recovered almost a decade ago between them that
still has yet to see print, largely because of time constraints and study
length, nothing like the week of time between notice and publication for
some of Cope's and Marsh's work that shows how hasty and erroneous they
were, forcing years of backtracking and synonymy because of the excessive
nomenclature that resulted from anything other than a monograph.
However, back to the embryo itself: there has yet to be a reason for any
amniote to alter from the observed trend of short snout/large orbit/huge
skull compared to skeleton with tiny limbs early in ontogeny to an
allometric reduction is skull and braincase/orbit size with an allometric
increase in limb and snout size. Rather, the models Peters offers show
that the babies are perfect miniatures of the adults. Often, segmentation
of vertebral series or phalangeal series is completely unfounded in the
tracings done, suggesting these are "completist" actions: making the
skeleton more "perfect" and complete than is actually observed. This
easily becomes an artifact of wishful thinking, like astronomers looking
into the heavens and just "knowing" that there were chariots pulling each
sphere and star through the heavens, despite not seeing them, or Percival
Lowell's observing canals and cities through the blur and obscurity of
Mars' atmosphere.
In many cases, as with portions of the Ediacaran, Burgess or Chengjiang
faunas, the "animals" represented tend to suggest more than they show, and
the observer starts to put what he thinks should go there once they have
an idea of the animal is seems to represent. In many cases, blobs can
represent soft-bodied animals or material debris that has since decayed
away. All logic suggests that the bony animal will leave a trace, often a
bone, or at least a definite impression of this shape (as in
*Scleromochlus,* in which every single one of the eight specimens is
preserved as a distinct impression, down to the last tiny palatal feature,
gastral rod, or dermal plate, and showing exactly how many haemal arches
were present during burial), but the artifacts on the slabs often only
show a patch of discoloration, common to all the slabs of the formation,
as well as occasionaly scarring, also common to most slabs.
So the challenge is this:
Rather than trying to get someone to corroborate the findings, we shall
try to find such artifactual organims in the slabs of other specimens
found at Solnhofen or Liaoning. No reasoning about what one should expect
to find, but anything that might be an impression should be noted. We can
even expand the search to other lagerstätten as in Chengjiang or Messell
or the Quercy deposits.
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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