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Protoavis & Drepanosauridae (sensu Renesto, 1999)



Patrick Mellor (patrickmellor@hotmail.com) wrote:
 
<When reading the 'portrait of Protoavis' in Chatterjee's The
Rise of Birds, it seems like virtually the whole skeleton is
known (although disarticulated). How is it possible that it is a
chimera when the skeleton seems so complete and so avian?
(unless Chatterjee is 'filling in' missing parts to fit with his
bird hypothesis and not mentioning it).>

  What has happened was that the specimens that Chatterjee has
designated type and paratypes are completely disarticulated but
located near each other in the same quarry. Locations relative
to each other in the quarry are unknown; for the most part, the
specimens were found as part of removal of overburden, not
through quarry mapping and careful excavation, as in the
collection of the *Bambiraptor* material. So the relations of
material are unknown. Whole specimens were designated from
relativity to one another, and apparent prescence of only a
single organism, scattered about, not by articulation. It
happens sometimes. The usual process is to designate them all as
separate specimens, and suggest affinity as a single organism,
designate a syntype series, then select one element as the
holotype. This has not been done. One resolution is to take the
most indicative element (skull of type) that Chatterjee _first_
and best described, and restrict the holotype to this, and
designate all other elements not found truly in articulation as
separate specimen numbers. One can reasonably allocate a set of
elements also found as paratypes to the strict hypodigm (as
paratypes), and still be able to argue for *Protoavis* identity
as a bird. One can then say: "Look, here we have a few elements
that appear to indicate the prescence of a bird, in the Dockum."
One hardly needs a whole specimen....

<....and I would be grateful if a listmember could explain the
basis of the case for the Protoavis remains being a mixture of
different archosaurs jumbled together, and why Protoavis has
remained in this strange position of being generally ignored for
so long.>

  Think about this one: in a single event, several organisms can
be embedded in a riverine mud and be permanently preserved for
210my ... You find such violent acts to dismember the elements
after the mud-dwelling creepers have got done with the
carcasses. So the elements get splayed about. I can think of
only a few autochthonous assemblages at the moment, but the
*Coelophysis* quarry at Ghost Ranch is an example where more
than just C was found in place, including elements of
*Syntarsus,* I believe *Rutiodon,* crocodiliforms, etc., and
these polychthonous assemblages will do precisely this: scatter
the remains to the four winds. *Syntarsus rhodesiensis* is
preserved in a scattered autochthonous assemblage, so that few
other elements besides S are found, and few of these really
articulated. These are deltaic riverine (silt) to lowland
riverine (mud and silt) to flashflood riverine (mud), and as
such make for interesting preservation conditions. The Dockum,
if I remember correctly, at the Post quarry (is *Protoavis*
found here?), is a series of scattered or layered mudstone and
sandstone fascies? Lacustrine typically is mud- and
sandstone....

  Okay, onto drepanosaurids....

  There are a few superficial features noted in the postcrania
and crania of the *Protoavis* paradigm, as Renesto (1999) takes
not in _Revista_. The skull has an extremely narrow parietal
with block like dorsal aspect, very broade, T-shaped frontals
that form the "lateral wings" that Chatterjee applies to the
lack of postorbitals; there are short curved ulnae with
olecranon processes, and a suspicious scapula with bent shaft
(curving forward or back?); and the cervicals have profiles and
aspects to their exterior that are dead-ringer for the
*Megalancosaurus* cervical series. Now, _all_ the cervicals but
the most posterior and axis/atlas have hypopophyses and those
wierd triangular neural spines ... all these are found in
*Megalancosaurus* (specifically, the type has them, and they are
corroborated in other specimens, including a complete,
articulated neck with dorsal series, pectoral girdle, and
forelimb [and a very unusal forelimb it is, too].

  This suggests that portions of *Protoavis* may be
drepanosaurid in nature.... The elements of *Dolabrosaurus* from
the Chinle are not immediately comparable from what I've seen (I
have only the paper by Berman and Reisz in _J. Paleo._), and
there is a partial pectoral girdle in press in _JVP_ from the
Chinle. These may allow us to compare what has been released on
*Protoavis* (which is to say, the scant large, good photos in
publication, not interpretive sketches or little photos, of some
of the lesser elements (manus, pes, ankle, etc.) to see if we
can disprove the idea they are elements of a megalancosaur. As
regards my previous statement regarding restriction of the type,
since the name bearer could be the holotype's cranium, which may
be megalancosaur in nature, the name *Protoavis* could be
applied to that taxon. Unless Chatterjee has other ideas.... :)

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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