RE: paleonet Origin of birds

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The debate is very one-sided. The evidence that supports birds arising from dinosaurs is very compelling. Recent finds (especially in northeast China) have lent strong support to the birds-are-dinosaurs argument.

I would add that the birds-are-dinosaurs phylogenetic argument has remained virtually unchanged over the past 30-40 years. Back in the late 1960's / early 1970's Prof. John Ostrom argued that birds evolved from theropods close to dromaeosaurids. He based this on the large number of shared anatomical traits between _Archaeopteryx_ (the first known bird) and _Deinonychus_ (a well-known dromaeosaurid). Since then, a long list of fossil discoveries have reinforced the bird-dinosaur link, including feathered theropod dinosaurs and sickle-clawed birds.

For a long time, opponents of the bird-dinosaur link argued that the similarities between early birds and dromaeosaurids was due to convergent (or parallel) evolution. Alan Feduccia and Larry Martin were particularly passionate about this. They claimed that _Archaeopteryx_ and dromaeosaurids were not at all closely related, and that _Archaeopteryx_ spent almost all of its time in trees, and dromaeosaurids spent all their time on the ground. The discovery of tree-climbing gliding dromaeosaurids (such as _Microraptor_) defeated that claim. Feduccia and Martin were forced to change their position. Now they argue that dromaeosaurids and birds ARE related after all - but that neither are theropods! They claim that maniraptorans (the group that includes birds, dromaeosaurids, oviraptorosaurs and related groups) evolved separately from the theropods (such as ceratosaurs, carnosaurs, coelurids, and tyrannosaurids)! They further argue that the similarity between maniraptorans and other theropods is due to convergence. I've yet to meet a single paleontologist who buys this argument. It's like arguing that humans evolved directly from lemurs, and have a separate ancestry to chimpanzees and gorillas.

In short, I find it very difficult to take the Feduccia-Martin view of theropod/bird evolution seriously.

Cheers

Dr Tim Williams

resperante <resperante@univ.llu.edu> wrote:

That is still an interpretation. In addition, many paleontologists and ornithologists do not agree with such interpretation.

Raul

-----Original Message-----
From: paleonet-owner@nhm.ac.uk [mailto:paleonet-owner@nhm.ac.uk] On Behalf Of Tim Williams
Sent: Wednesday, April 13, 2005 3:55 PM
To: paleonet@nhm.ac.uk
Subject: RE: paleonet Origin of birds

Larry Martin's "landmark" analogy is sidestepped when you realize that _Archaeopteryx_ is BOTH a bird and a dinosaur. Birds are dinosaurs, so the issue is moot.

Cheers

Tim

resperante <resperante@univ.llu.edu> wrote:

So, how can the study of MODERN organisms provide clues about the evolution
of flight millions of years ago? I wonder if the amount of inference and
assumptions is higher than the actual evidence bones provide to answer the
question.

A few months ago I read Larry Martin's statement cited in Pat Shipman's book
Taking Wing (p. 102), which is very relevant to this issue:"The very first
thing you do, when you look at a map or anything unknown, is that you
recognize all the familiar landmarks that you've already seen. Now if you've
never worked on birds, and you've worked on dinosaurs, when you look at
Archaeopteryx, you're going to see the dinosaur. And if your primary work is
on birds, then when you look at Archaeopteryx, you're apt to see the bird."

If that is the case with Archaeopteryx, I wonder if the same is applied to
inferring evolutionary trends through comparative studies of modern or other
ancient birds. The issue is that evolutionary inferences (interpretations)
are as subjective as the evidence from the specimens is.

Raul Esperante

-----Original Message-----
From: paleonet-owner@nhm.ac.uk [mailto:paleonet-owner@nhm.ac.uk] On Behalf
Of Dinogeorge@aol.com
Sent: Tuesday, April 12, 2005 11:16 PM
To: paleonet@nhm.ac.uk
Cc: Dinogeorge@aol.com
Subject: Re: paleonet Origin of birds

In a message dated 4/12/2005 9:19:46 P.M. Pacific Standard Time,
jpenkethman@ispwest.com writes:

>>If anyone has time for this: How can you tell whether it was the
>>ancestor
of
the flightless bird that could fly, or it will be the descendants that
would become capable of flight. In other words, how can you tell the
direction of evolution from a fossil?<<

You can't. You can't even tell from a cladogram. You have to reason from
physical principles, and from known evolutionary trends in modern
organisms.

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