Re: EARLY EVOLUTION OF 'BIRDS'

["John V Jackson" <jjackson@interalpha.co.uk>]

--Original Message-- From: Matthew Troutman <m_troutman@hotmail.com>Date: 06
November 1998 01:23



> [Siriraks Arrathrakorn said...]
>>>After I have read some papers. I see that many fossils have feather
>>>and may be origin of bird.
>
>>[JJ said]This is what many people say.  But many people are often wrong!
>
>[MT said]I agree to an extent with this if I understand your standing
correctly.
>
>>Yes - they come after the first bird.  Not just some of them but all of
>>them.  This means probably the origin is the other way round - these
>>feathered dinos are *descendants* of birds.
>
>This could just be an example of a preservation bias.  Anyway, you
>cannot use the fact that the birdlike dinosaurs came after
>_Archaeopteryx_ as proof that they are descendents of _A._.  More
>evidence should be gathered.  Thus far, I think that the evidence shows
>that these creatures are long-surviving relicts that were close to the
>ancestry of birds.

As absolutely no-one commented on my post of last month which dealt with
this, I'm repeating it now.  One or two temporal anomolies can be expected;
50 or 100 or 200 look like evidence: [For 'maniraptorans', read
'Arctometatarsalia + Maniraptora', as used by TMKeesey in his web site]

[[start of inclusion...
Matt Troutman: 4/10/98:

>Another weakness of your hypothesis is its interpretation of secondary
flightlessness in maniraptoriforms. A far better interpretation is that
they are avian ancestors not avian descendents.
<

Just for a moment considering the chronological order of appearance in the
fossil record (I?m referring to the non-pre-Archaeopteryx appearance of
maniraptorans), how many paradoxical instances make a piece of evidence?

Jurassic fossils are rarer than Cretaceous fossils; it is also
hypothetically possible that if we assume maniraptorans gave rise to birds,
it may have been early in maniraptoran existence (though the more this is
true, the weaker the case ? see below).

(By chance, only a small fraction of the evidence appears between
Archaeopteryx and the end of the J (assuming the China stuff is K) so the
principle needs only slight re-phrasing to refer to either ?Pre-Archae? or
?Pre-K?).

Say the ratio of maniraptorans living in the K to those living in the J was
A:B;
Say the ratio of the chances of an indiv living in the K ever being found to
that of one in the J is C:D;
The ratio of the chances of a maniraptoran we have found coming from the K
to from the J is (A/B)*(C/D).
The probability of any maniraptoran we have found coming from the K is  1/(1
+ 1/ ((A/B) * (C/D)) ).

The chance of N maniraptoran fossils all appearing after Archaeopteryx is
this expression raised to the power of N.

It is interesting to plug various values into this:

A/B=3.01; C/D=2; N=30;  gives a probability of 0.01  .   Very unlikely, and
bad news for BADD.

However, perhaps a more friendly set of inputs would be if K mani?s were 100
times as numerous as J ones, and the the K was 5 times as fossiliferous as
the J:

A/B=100;  C/D=5;  N=30;  gives a probability of 0.941  . Fine for BADD ?
sort of.  However this combination assumes maniraptorans hardly existed
pre-Archaeopteryx!!  And maybe N should be much bigger than 30.

Perhaps the hypothetical pre-Archae maniraptorans were difficult to find
because they were very small, and/or lived in conditions unhelpful for
fossilisation ? they were living in forest trees for example. . . !!!
Whatever assumptions we make, a BCF-type explanation is the only answer,
using these probability calculations.  Maniraptorans therefore did not give
rise to birds since they all postdate the first bird ? unless they were
effectively early birds already.

To return to the original quote, a far better interpretation is that
maniraptorans *are* avian descendents (though not necessarily pterosaur
descendents).

There have been claims of pre Archae. Jurassic maniraptorans, largely in the
form of teeth, often unusually small.  You may call them maniraptoran but
they will probably be small aerial forms, or larger non-arborial descendents
of them.

JJ
...end of inclusion]]

Plug in your choice of parameter for preservational bias.  There's a PhD in
there somewhere, by the way!


>You cannot look at _Archaeopteryx_ and get a perfect
>dromaeosaur, _A._ is too birdlike and derived.

Reversible derivations for flight.

>
>>This is not what I think because there were two very big explosions,
>>both just after the first bird known:  other birds, and bird-like
>>dinosaurs. I would expect this - feathers give an animal great
>>advantages no other animal has, and drives evolution in new
>>directions.
>
>Of course, you have to show that the birdlike dinosaurs evolved from the
>first-known bird.

We..ell, it cannot be proved positive until an unbroken pavement of
undeniable links is discovered - but the same goes for either theory.  Of
course, if one wanted to be sniffy one could say one didn't have to prove
anything (again)  :-).


>
>>All birds are descended from a very close relative to >_Archaeopteryx_.
>Many so-called "dinosaurs" are also.  The fact >that cladistics doesn't
>agree with this will be evidence that cladistics >is bad (when proof
>appears).
>
>Where is your proof other than the temporal 'problem' (?) ...

That's a lot more proof than one usually gets.  Most scientists would say
those statistics were pretty damn convincing.


>...and the existence of feathers?  Here's what I see;
>
>_Archaeopteryx_ is extremely birdlike with the hooked ectopterygoid, no
>serrations on teeth, etc, birdlike braincase, single sternum, etc.
>etc...
>
>Advanced birdlike dinosaurs show few of these features.


All reversible flight adaptations.  (We've been here before ... many, many
times!)

JJ