This was bounced back. I am sending it again. Sorry if anyone gets it
twice.
On Fri, 26 Dec 1997 21:40:37 -0600, John E. Rylander wrote:
[...]
JR>Lung Fossils Suggest Dinos Breathed in Cold Blood
>
>Science 25-DEC-97 By Ann Gibbons
>
>When John Ruben first laid eyes on a high-quality photo of the
>so-called "feathered" dinosaur from China last yea....the theropod
>dinosaur's innards, which were outlined in the slab of stone....here
>was the first evidence in the soft tissue that theropods had the
>same kind of compartmentalization of lungs, liver, and intestines
>that you would find in a crocodile"--and not in a bird.
Interesting. Perhaps the theropods were not even closely related to
dinosaurs, but shared a more ancient last common ancestor with
crocodiles? If so, the close resemblance of theropods to birds is is
yet another example of convergence, which Dawkins admits is
"worrying" (Dawkins R., "The Blind Watchmaker", 1991, p94), because
if it may be impossible to tell what similarities are due to close
ancestral relationship, and what are due to other factors.
This is yet another salutary lesson that one cannot be sure of what
is descended from what without evidence from the animal's soft
anatomy. This precisely was Denton's claim regarding the origin of
birds:
"The systematic status and biological affinity of a fossil organism
is far more difficult to establish than in the case of a living
form, and can never be established with any degree of certainty. To
begin with, ninety-nine per cent of the biology of any organism
resides in its soft anatomy, which is inaccessible in a fossil.
Supposing, for example, that all marsupials were extinct and the
whole group was known only by skeletal remains would anyone guess
that their reproductive biology was so utterly different from that
of placental mammals and in some ways even more complex? Modern
birds differ greatly from reptiles in many physiological and
anatomical characteristics, particularly, for example, in their
central nervous, cardiovascular and respiratory systems...but,
because information about the soft biology of a fossil form is
difficult to obtain from its skeletal remains, to what extent
Archaeopteryx was avian in its major organ systems will always be
largely a matter of conjecture." (Denton M., "Evolution: A Theory
in Crisis", 1985, p177)
JR>To prove that notion, Ruben and his graduate students sectioned
>crocodiles and other reptiles and found that their lung structures
>resembled the images of several flattened fossil dinosaurs from
>China. On page 1267, Ruben uses this lung evidence to argue not
>only that dinosaurs were incapable of the high rates of gas
exchange needed for warm-bloodedness, but also that their
>bellowslike lungs could not have evolved into the high-performance
>lungs of modern birds. Thus, he challenges two of the reigning
>hypotheses concerning dinosaurs: that they were warm-blooded and
>that they gave rise to birds.
But this lung evidence seems to indicates that "crocodiles and other
reptiles" and "dinosaurs" (but not birds), shared a last common
ancestor, and that the ancestor of birds predated even it. So this
argues not only against birds descending from dinosaurs, but even
from crocodiles, which is one theory:
"A British paleontologist, Dr Alick Walker of the University of
Newcastle, in 1972 proposed that modern birds were more closely
related to a group of Triassic crocodiles. He had been involved in a
detailed study of the Triassic crocodile Sphenosuchus, and was able
to point to a number of unexpected similarities in the form and
arrangement of the skull bones in birds and this fossil. This
provoked him to look in greater detail at the structure of living
birds and crocodiles. Numerous similarities were indeed brought to
light, in the structure, fore limbs, and ankles of embryonic birds
and crocodiles. His principal suggestion based on this careful work
was that the ancestors of birds and crocodiles seem to have adopted
one of two ways of life. One group of rather slender, lightly built
crocodile-like creatures adopted the habit of tree climbing, and
ultimately became birds; while the other became larger amphibious
types and developed into what we would now regard as typical
crocodiles." (Norman D., "Dinosaur!", 1991, p197).
If this is upheld, it means that the earlier theory of Heilmann that
birds may be a separate group which goes right back among the
archosaurs of the late Permian-early Triassic, ie. about 250-230
mya.
"Heilmann selected a more general group of reptiles, which were
ancestors of dinosaurs, crocodiles, pterosaurs, and several other
groups, and which are usually called archosaurs. They were abundant
during the Triassic Period. Some, such as Euparkeria, seem
relatively light and agile and, since they have collar bones, are not
disqualified for that reason from bird ancestry. The choice of such
early creatures as ancestors also suggested that birds go back
farther than Archaeopteryx, as Huxley had believed. This raised the
possibility that Archaeopteryx may have been an early evolutionary
offshoot from the main line of birds, and perhaps not as typically
primitive as was first thought." (Norman D., "Dinosaur!", 1991, p196)
JR>Coming hot on the heels of another controversial paper that
>concludes that digits in bird wings could not have developed from
>dinosaur forelimbs (Science, 24 October, p. 666)
Thanks for this reference too. This is another good point. A
reptile's foreleg is oriented down and forward, whereas a birds'
wing is up and backwards. A series of functionally advantageous
transitional states between these two extremes is difficult to
imagine. Perhaps this is what Gould and Eldredge had in mind when
they wrote:
"At the higher level of evolutionary transition between basic
morphological designs, gradualism has always been in trouble, though
it remains the "official" position of most Western evolutionists.
Smooth intermediates between Bauplane are almost impossible to
construct, even in thought experiments; there is certainly no
evidence for them in the fossil record..." (Gould S.J. & Eldredge
N., "Punctuated equilibria: the tempo and mode of evolution
reconsidered", Paleobiology, 1977, vol. 3, p147)
JR>...Ruben's report is part of a "one-two punch to the dinosaur
>origins of birds hypothesis," says paleontologist James Farlow of
>Indiana University-Purdue University in Fort Wayne. But while many
>dinosaur experts say they welcome Ruben's novel approach, few are
>willing to embrace his conclusions so far. "This is exactly the
>kind of research we need," says Lawrence Witmer, an evolutionary
>biologist at Ohio University College of Osteopathic Medicine in
>Athens. And it's definitely weakening the case for warm-blooded
>dinosaurs. But many researchers, including Farlow and Witmer,
>think there's persuasive evidence that birds are descendants of
>dinosaurs. Says Farlow: "[This] is like a breath of fresh air,
>but it's going to ruffle a lot of feathers."
While I provisionally accept some form of common ancestry between
major groups like reptiles and birds, I would not be surprised if it
does not support a Neo-Darwinian "blind watchmaker" pattern. My
expectation is that the gulfs between major groups will turn out to
be consistently further back in time than first thought (and
hence deeper and wider) and will be better explained by a
Pre-Darwinian "archetypal" (or structuralist) model:
"The reason for this failure is, as we have seen, that the orthodox
theory assumed homologous structures in different species to be due
to the same 'atomic' genes inherited from the common ancestor (though
modified by mutation in the course of their long descent); whereas
there is now ample evidence that homologous structures can be
produced by the action of quite different genes. The only way out of
this cul-de-sac seems to be to substitute for genetic atomism, which
has so drastically broken down, the concept of the genetic
micro-hierarchy, with its own built-in rules, that permit a great
amount of variation, but only in limited directions on a limited
number of themes. This really amounts to the revival of an ancient
idea which goes back to Goethe-and even further to Plato." (Koestler
A., "The Ghost in the Machine", Arkana: London, 1967, p137)
Happy new year!
Steve
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