>> Jim
JF>It's worth noting that Martin *may* have a bias towards evidence
>that would indicate an older (than mid-Jurassic) age for birds. He
>is well known as one of the hold-outs against the idea of a
>dinosaurian origin for birds. (I think he is in favor of a more
>crocodilian-type ancestor for birds; yes, I know that sounds silly;
>no, I don't agree with it)
>> Thanks for this background. But why is believing that birds did not
>> evolve from dinosaurs necessarily "bias"? He might be right and all
>> the others biased! :-)
Quite true, I'm trying not to be dogmatic. Believing that birds did not
evolve from dinos is not bias, but it could (I'm not saying it did) bias
his evaluation of the new evidence.
JF>Although Archaeopteryx is considered a superb example of a
>reptile-bird intermediate, I have heard claims that it is *not*
>considered to be a direct ancestor of all later birds (I do not know
>why). Archae and this new find could have a somewhat older common
>ancestor.
>> I understand, that: a) it is contemporaneous with its putative
>> ancestors and b) it is too specialised.
I agree with b), although I don't know which features led to the
conclusion. If a) is true, it has no effect on Archie's relationship
with birds (only with the dinos). There are occasional claims that
Archie is contemporaneous with it's *descendants*. The commonest source
of such a claim is Proavis (or is it Protoavis?), which is a scrappy
fossil over 200 million years old. Few paleontologists accept this as a
bird; I think Larry Martin is one of the exceptions.
JF>This is an over-simplification of evolutionary theory. Assuming
>the beak evolved for some survival value, the later extinction of
>some branches doesn't tell us anything about the beak; it could have
>happened for many other reasons (e.g. disappearing food source).
>> That is not what the article says:
>> "The new discovery suggests that the features we associate with modern
>> birds have probably evolved and disappeared several times, says
>> Martin. Some advanced characteristics, such as true bills, evolved
>> early on in groups that subsequently died out."
I stand by my statement; the above quote says nothing to imply that
these groups died out because the beak lost it's survival value.
JF>Hang on, we're talking *10 million years*, almost twice the time it
>is thought to have taken humans to evolve from apes. Evolving a beak
>seems a trivial change, compared to that. Our sampling density (two
>species, in tens of millions of years) can hardly be expected to give
>us a good handle on the fine details of the evolution of birds.
>> No. We may be talking only of "just a few million years after
>> Archaeopteryx made its debut"
No, the article you quoted said:
These deposits are difficult to date accurately, but the researchers
believe that Confuciusornis lived about 10 million years after
Archaeopteryx, which appeared around 145 million years ago.
>> of a trait that previously was thought to have taken "75 million
>> years after Archaeopteryx".
No, the first beaked bird was found 75 My after Archie. That's very
different from saying it needed, or took, that long to evolve.
-- Jim Foley Symbios Logic, Fort Collins, COJim.Foley@symbios.com (303) 223-5100 x9765 I've got a plan so cunning you could put a tail on it and call it a weasel. -- Edmund Blackadder