RE: Hoatzin & Archaeopteryx

[Tim Williams <twilliams_alpha@hotmail.com>]

Amtoine Grant wrote:

> Just thinking, has anybody compared the skeletons of Archaeopteryx. 
> Especially with the controversy regarding manual digits 1,2,3 & 4 in 
> theropods & extant birds, this could prove interesting.

The "controversy" is somewhat of a red herring.  The DML archives should be 
helpful in pining down the references.

> I've been wondering if the Hoatzin could be a late-surviving 
> Archaeopteryid[to coin a phrase] -

If only that were true.  Alas, not a chance.  _Opisthocomus_ is a 
card-carrying member of the Neornithes - although its closest affinities 
(whether cuckoos, seriemas or something else) are still murky.

> As a side note, not much has been said of Protoavis. I understand that the 
> remains are fragmentary. Can it be discerned from what information is 
> available whether Protoavis may have possibly been an ancestor of 
> Archaeopteryx,

One problem is that the total material assigned to _Protoavis texensis_ may 
include parts of several different animals.  For example, some bits look 
like they come from a drepanosaur, other bits look more dinosaurian, and 
others ... who knows?  Chatterjee's reconstructions certainly make 
_Protoavis_ appear very bird-like (and more advanced in form than 
_Archaeopteryx_), but most researchers have grave doubts concerning the 
accuracy of his reconstructions.  Unlike _Archaeopteryx_ and the Liaoning 
maniraptorans, the two specimens of _Protoavis_ (one larger than the other) 
were found dissociated and strewn over a fairly wide geographical area.  
There may be maniraptoran (and perhaps even avialan) material among the 
bones referred to _Protoavis_.  If there were Early Jurassic therizinosaurs, 
why not Late Triassic birds?  The material certainly requires further 
revision.  However, _Archaeopteryx_ still holds the honor as the oldest 
undisputed bird.

> or an example of convergent evolution, as in phytosaurs & crocodilians?

The heads of drepanosaurids (and _Longisquama_) are superficially very 
bird-like - which is why Senter coined the name Avicephala for the clade 
containing these critters.  Drepanosaurids also show narrow neck vertebrae 
that bear hypapophyses - also as in maniraptorans.  Certain features may 
prove to be convergent between birds and _Protoavis_, but first we have to 
determine what _Protoavis_ actually is.


Tim


Tim