I am catching up after my 3 months holiday on my scientific journal
reading. I was interested to read in New Scientist of an recent
article in SCIENCE that there is even more evidence that birds did
not come from dinosaurs, because the presumed nearest dinosaurs to
birds, the theropods, are missing different digits:
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Dinosaur theory put to flight
Birds may not be descended from the ancient reptiles after all
Jonathan Knight
TRADITIONAL thinking about the ancestry of birds has been challenged
by biologists in the US. They say that a comparison of dinosaur
claws with bird Willgs and feet contradicts the Widespread theory
that birds evolved from small, flesh-eating or almost vanished,
during evolution.
But now Ann Burke and Alan Feduccia of the University of North
Carolina at Chapel Hill have found that birds and theropods are
missing different digits. "As a result, it's almost inconceivable
that one group week's Science (vol 278, p 666), Burke and Feduccia
show that this holds true across a wide range of species, including
alligators, probable descendants of the first dinosaurs.
Using the primary axis as a guide, the researchers found that the
outermost digit in three very different bird species-chicks,
ostriches and cormorants-corresponds to the fourth digit. In other
words, birds have retained the middle three digits during evolution.
The outer two, numbers one and five, have almost entirely
disappeared.
But dinosaur fossils tell a different story. In theropods, the
fourth and fifth digits are greatly diminished or have disappeared
altogether. Feduccia maintains that animals which had lost these
digits could not then evolve into birds that lack one and five.
Other experts agree. Peter Dodson, a dinosaur palaeontologist at the
University of Pennsylvania School of Veterinary Medicine in
Philadelphia, has long favoured the notion that birds descended from
theropods. "That has been the prevailing faith for the past twenty
years," he says. But the work by Burke and Feduccia is leading him
to reconsider. "They are doing a first-class job of shaking things
up and making us re-examine the evidence."
Feduccia says that dinosaurs and birds have many similar features and
probably do share an ancestor that gave rise to both. But if there
was such an animal, we have yet to find its fossils."
(Knight J., "Dinosaur theory put to flight," New Scientist, Vol. 156,
No. 2106, 1 November 1997, p20)
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I apologise if the above has already been posted (the last I checked
the archive at http://www.calvin.edu/~grayt/mailevolution/ was not
current).
I haven't yet seen the SCIENCE, article, but from the above New
Scientist summary, I presume their respective foot digit pattern is
something like as follows (best viewed with monospaced font):
Dinosaurs Birds
5 4 1 5
\|/ \|/
/|\ /|\
/ | \ / | \
1 2 3 2 3 4
If that is the case, it is a significant difference. If all living
and fossil reptiles and mammals share the dinosaur digit pattern,
then either: a) a radically different digit development pattern can
arise spontaneously-which would play havoc with tracing common
ancestry; or b) it pushes the last common ancestor of all birds back
before the last common ancestor of all reptiles and mammals.
In view of other evidence about the soft anatomy of dinsosaurs being
radically different from birds (see post re "Lung Fossils Suggest
Dinos Breathed in Cold Blood", Science 25-DEC-97 By Ann Gibbons), the
latter seems the more likely scenario.
If it is the case that birds did not arise from dinosaurs, then
evolution has a big problem. Archaeopteryx has since Darwin's day
been hailed as the link between dinosaurs and birds:
"In 1861 the famous early fossil bird Archaeopteryx ("ancient
feather") was discovered in limestone quarries in Bavaria. In the
same year another small (2ft, 60 cm long) complete fossil reptile
skeleton was discovered in the same area of southern Germany and was
named Compsognathus ("pretty paw"). Both Cope and the English
anatomist Thomas Henry Huxley (1825-1897) realized in the early 1860s
that Compsognathus was not just any reptile, but a tiny dinosaur. It
was lightly built, with long, bird-like legs and feet and a similar
posture to that of Hadrosaurus and Laelaps. This suggested that
there were greater similarities between birds and dinosaurs than
between mammals and dinosaurs, as Owen believed." (Norman D.,
"Dinosaur!", 1991, p78)
Leading palaeontological authority Carroll says several time that
Archaeopteryx is essentially a dinosaur with feathers:
"...only a single species, Archaeopteryx lithographica represents the
transition between dinosaurs and birds." (Carroll, R.L., "Vertebrate
Paleontology and Evolution", 1988, p4)
"Were it not for these feathers, Archaeopteryx would not have been
recognized as a bird, as is demonstrated by the fact that one nearly
complete skeleton in which the feathers were not recognized was
initially identified as a dinosaur. In fact, there are no features
of the bony skeleton of Archaeopteryx that are uniquely avian. All
have been described in genera that are classified among the
dinosaurs. If all elements of the skeleton were considered of
equivalent value in classification, Archaeopteryx would certainly be
considered a feathered dinosaur." (Carroll R.L., "Vertebrate
Paleontology and Evolution," 1988, pp338-339)
"The earliest known fossil bird is Archaeopteryx from the Upper
Jurassic of Germany. Its flight feathers were extremely similar to
those of modern birds in their structure and distribution, but the
skeleton was almost identical with those of small theropod dinosaurs
such as Compsognathus." (Carroll, R.L., "Vertebrate Paleontology and
Evolution," 1988, p357).
If Archeopteryx is only distantly related to a dinosaur like
Compsognathus, yet is virtually indistinguishable from it, then how
can evolutionists be sure about the relationship of any fossils?
Dawkins admits that this type of "massive convergence" is "worrying":
"If taxonomists use resemblances to measure closeness of cousinship,
why weren't taxonomists fooled by the uncannily close resemblances
that seem to unite these pairs of animals? Or, to twist the question
round into a more worrying form, when taxonomists tell us that two
animals really are closely related- say rabbits and hares - how do we
know that the taxonomists haven't been fooled by massive convergence?
This question really is worrying, because the history of taxonomy is
replete with cases where later taxonomists have declared their
predecessors wrong for precisely this reason...Who is to say that
future generations of taxonomists won't change their minds yet again?
What confidence can we vest in taxonomy, if convergent evolution is
such a powerful faker of deceptive resemblances?" (Dawkins R., "The
Blind Watchmaker," 1991, p269).
Good question! This discovery should have *very big* adverse
implications for evolutionary theory.
Happy new year.
Steve
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| Stephen E (Steve) Jones ,--_|\ sejones@ibm.net |
| 3 Hawker Avenue / Oz \ Steve.Jones@health.wa.gov.au |
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