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RE: Hoatzin & Archaeopteryx

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.