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re: smallest pteros



Dave Peters (davidrpeters@earthlink.net) wrote:

<There is evidence -- the proxies I've mentioned, and the plots by Jouve
-- that it's a juvenile. What evidence is there that says it's adult?>

  My observation tells me this is a fairly well-ossified animal. So given
the previous arguments from Dave regarding juveniles lacking ossified
bones, why is the Jouve *Ctenochasma* a juvenile, if it's ossified?

  Previous posts have asked for a method to determine how you find an
adult versus a juvenile bone, and I have refrained from answering for a
while. But, hasn't the answer been obvious? We have been arguing about
juvenile bone texture and adult smoother, finished bone, for the last
several months. Papers have been cited and work used that shows that
birds, crocs, and lizards, as well as amphibians and mammals, show the
same juvenile to adult ossification patterns in bone texture that supports
that, IF pterosaurs are reptiles even, they _should_ be inferred to have
the same condition, unless otherwise demonstrated. Dave has used evidence
that no one else can corroborate to "otherwise demonstrate" this
condition, and argue that adults also have unfinished juvenile bone
texture, aka, "woven" bone. This evidence MUST be corroborated, or put
aside, as is wont in science.

<show me that a baby 'anything' would show up "in all trees." If you can't
show me, as I have shown you with a cladogram, then this is only cocktail
chatter. Not science. Really, David, I'll wait until your exams are over.
Or send me the refs.>

  In Dave Peters' defense, I must say I've not seen such references
myself. I will shortly be practically testing this, but have used my own
anecdotes to support my argument without actually providing references. In
my argument, cats have been used rather than chimps, in that adult wild
cats and juvenile "big" or pantherine cats have similar proportions,
rather than juvenile feline cats or adult patherine cats being grouped
with their own closest kin. The most ideal test of this theory is to take
a juvenile feline, a juvenile pantherine, and their adult counterparts,
and scale them to one another. Add in, say, an acionychin like *Puma,* and
*Lynx* for scaling adult size, and we should arrive at an adequate adult
and juvenile scaling curve for all major limb and body segment parts to
see if, indeed, juveniles scale together and if the patherines are
peramorphic. This work has been done to some degree, I just don't remember
where, but it should make an interesting project. I will be heading to the
Multnomah County Library in a few moments to look in on this subject.

  Here's an example of instantly relating allometric scaling: horses in
their development range from extremely large-headed, long-legged animals
and become increasing larger-bodied relative to head- and leg-length, as a
result. That means their spine and internal organs have a greater rate of
allometric size increase than do the extremities. There is no isometry
involved, where you just "scale up" in size without a differential
increase or decrease in lengths compared to other portions of your
anatomy. Isometric scaling, in fact, tend to be rare in terrestrial
vertebrates, because of the bone structure versus loading changes as the
bone increases in diameter and size for a given weight. So pterosaur
juveniles looking like "scaled down" adults would also tend to be
unparsimonious.

<David, you've fallen into a classic cladistic trap that Unwin, Kellner,
Senter and many others have likewise fallen into. You've carefully chosen
your characters!  And you've limited the number of characters to a mere
few. What you must do instead, and what all future cladograms should do,
is to look at every body part from rostrum to toe ungual and code as many
'not very carefully chosen characters' as possible (say over 150 to be
safe) and only then will you see that the vast majority of characters in
closely related taxa are indeed the same!>

  Mickey and I have discussed the advisability of using "every character
in the book" for a few years. Since the early 90's when a lot of
"carnosaur" characters turned out to be based on animals reaching or
attaining a large size, it has been considered practical to leave out
characters which change when animals attain large sizes, known as
"size-related characters." Including these characters in a matrix favored
grouping animals merely because they were big, without scoring "big" and
"small," (the original dichotomy of carnosaur versus coelurosaur, in
fact), would skew the analysis away from size-independant characters
[example, "apically vertical fluting on the lingual surface of the first
2-3 mesial teeth"]. For instance, in both *Albertosaurus* and
*Allosaurus,* teeth become relatively thicker given their length above the
root as overall size of the animal increases; this is exaggerated in
adults of "tyrannosaurines" like *Daspletosaurus* and *Tyrannosaurus.*
However, leaving these out leads to a problem: what if the characters
were, while being related to size, ALSO phylogenetically informative?
Could they apply in a phylogenetic sense? Say, that at adulthood, a mean
length of 40 ft. was an informative character in hadrosaurine
hadrosaurids? There are "robusticity" measurements, circumference/length
indeces in limb bones or mean length of skull to femur, that can fall into
this category, but as it is clear with some theropods like spinosauroids,
skull length to femur can be informative, even if its general to other
theropods.

  Dave would be right on one extreme: Use as many characters as you can.
Because they may all be informative. But beware that such will create
varying amounts of homoplasy in some cases, pulling some taxa together
because they are small, or because they are big, or because they are
juvenile, or because they are adult.

<you (and I) don't know what the young were using their nonvolant wings
for, but if you watch baby birds you can see that they indeed use their
wings to communicate their needs long before they can fly with them.>

  Another parallel with cats applies here: my kittens have always clutched
and gripped with their limbs long before they could walk. Oddly enough,
they also have mostly ossified diaphyses.

<not sure, that's why I ask the question of the experts>

  But the "litmus test" is a critical answer, since Dave Peters has called
into questions the identification of juveniles. There must be a metric or
a condition that HE uses to determine adult from juvenile. Just above he
called the Jouve *Ctenochasma* a juvenile, and the "embryo" *Avgodectes*
and adult in a published article. So, the argument must be clarified by
Dave, not other "experts."

<and the alternative is??? voodoo? opinion? dogma?  Stay with science,
David. Cladistics may not be perfect (especially the way some people
practice it,) but it's the best we have. You're free to disagree, but you
better have better evidence>

  There is no "voudoun" opposite to cladistics. Cladistics IS something
that requires interpretation, and massive amounts of it. Why? Because of
your choice of characters, selection of taxa, and how you choose to
interpret features. In many cases, coding from ephemera can be just like
reading tea leaves, or whether that knob on a bone represents a condyle or
just a "bump" that doesn't articulate. Like the varying interpretations of
basal tetrapod humeri.

  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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