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Re: Hoatzin & Archaeopteryx



----- Original Message -----
From: "Tim Williams" <twilliams_alpha@hotmail.com>
Sent: Thursday, December 30, 2004 7:37 PM

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

The name Archaeopterygidae exists. It just wasn't used for decades because it was thought to contain nothing but Archie itself. Now that *Wellnhoferia* is thought to be separate, this might change.


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,

Interestingly, Chatterjee himself thinks (or at least thought in 1997) that *P.* is more closely related to the living birds than (to) *A.*. There are indeed several features that individual bone fragments referred to *P.* share with living birds while *A.* lacks them. Some can't even be found in Cretaceous birds.


Besides, you probably don't know _how_ fragmentary some of the parts are. The ilium was glued together from a dozen individual crumbs that don't always have fitting edges.

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?

The head and neck are certainly drepanosaurid. Part of the rest seems to come from a coelophysid or so. Other parts have not yet been investigated... but I'm in any case sure that the animal is chimeric because the lower legs are much too big for the femur and pelvis.


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.

One at least was found in a clump. But it includes the drepanosaurid head and neck as well as seemingly coelophysid limb parts.


There may be maniraptoran (and perhaps even avialan) material among the
bones referred to _Protoavis_.

The foot is a good candidate for belonging to a bird... if we trust Chatterjee's drawings. Chatterjee usually doesn't make clear how much of each bone is actually preserved.


If there were Early Jurassic therizinosaurs,
why not Late Triassic birds?

Oh yes. But then *Eshanosaurus* shared only one character with therizinosaurs and not with prosauropods last time it was discussed here.


However, _Archaeopteryx_ still holds the honor as the oldest
undisputed bird.

If we define "bird" in a way that potentially includes dromaeosaurs and probably oviraptorosaurs... and if we can keep *Epidendrosaurus* out. Otherwise I don't agree with "undisputed". :-)


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.

In addition, these vertebrae are heterocoelous, large and numerous. (This is interpreted as an adaptation to high neck mobility -- drepanosaurids are thought to have been similar to chamaeleons, but while the latter shoot only the tongue forward, drepanosaurids apparently used with the entire head and neck. The likewise highly mobile necks of birds are thought to replace the missing hands for grasping.) They are, in fact, more heterocoelous, large and numerous than in most or all Early Cretaceous birds (and fit drepanosaurids in these respects).