Re: Sphenochians and birds

["Zoe Heraklides" <z_heraklides@hotmail.com>]

Jean-michel BENOIT" <Jean-Michel.BENOIT@gemplus.com> writes:


> I was re-reading recently a _quite_ old but interesting book written by the 
> Cserkases with help from Olson. It spoke of a possible origin of birds 
> within the sphenosuchians,

This theory (which walker supported for a time) is now widely discredited.   
Sphenosuchians like Terrestrisuchus (which you mention) are basal 
crocodylomorphs.

> the fossil called *protoavis*, having elongated forelimbs thus thought to 
> have had a arboricole ( is this the correct word? ) life but found with no 
> evidence of feathers.

Protoavis is thought by Chatterjee to possibly arboreal and undoubtedly 
volant (i.e. able to fly).  The idea that Protoavis is a bird has received 
very little support in the paleontological community.  The true identity of 
Protoavis is still uncertain - it may be made up of bones from more than one 
species.

> It was thought to be derived from animals like *terretrisuchus* placing the 
> first bird-like reptiles back to the triassic period.

Even Chatterjee believes birds to have evolved from dinosaurs, not 
crocodilians.

> The text said that embryology showed that the missing fingers in birds were 
> not the same as in theropods but were the same to those of crocodilians.

This is probably not correct.  Certain opponents of the birds-from-dinosaurs 
theory claim that the homology of the fingers differs betewwn theropods and 
birds (I-II-III vs II-III-IV).  The embryological basis for this in birds is 
controversial, but I think it's fair to say that the embryological evidence 
is reconcilable with the I-II-III origin of the digits in birds (as in 
theropods).  There are some recent papers which discuss this.


> I'm not very sure I've understood all the scientific explanations but it 
> seemed very convincing to me. How about this theory? Is it still debated or 
> has it been abandonned for ever?

It has been largely abandoned, but never say forever!

ZH



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