[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


Jeez....  it seems like every month or so I have to repeat to people the same
exact thing.....

charger72@juno.com worte:

<< I have to agree (this time). The ONLY thing that makes archeopteryx a
 bird is the feathers. It has NO other bird-like characteristics. The
 wishbone is the only other skeletal feature and that is the same for most
 if not all theropod dinosaurs. Yes, archeopteryx shows a link between
 dinosaurs and modern birds, but whether those features are the result of
 parallel evolution or desendency is yet to be proven. >>

There are in fact three very subtle characters present in _Archaeopteryx_
that clade it closer to modern birds than either is to dromaeosaurs.  They

1) loss of the cranial process of the pubic boot making it look like a J in
lateral profile.  This feature is also found in "Linsterosaurus", the flying
raptor, _Adasaurus_, _Unenlagia_ and modern birds.  It is not found in other
tetanuran theropods including dromaeosaurs or alvarezsaurs.

2) appearence of the proximodorsal process of the ischium (incidentally, a
defining feature of the clade Saurirae, thus indicating it is probably
paraphyletic).  This is a small knob on the dorsal surface of the ischium
near the illiac peduncle.  It is found in _Archaeopteryx_, _Unenlagia_, and
modern birds.  I do not know the condition in "Linsterosaurus" or the flying
raptor.  It is not seen in _Adasaurus_, dromaeosaurs, alvarezsaurs or any
other theropods.

3) distal migration of the obturator porcess of the ischium.  This feature is
seen only in _Archaeopteryx_ and modern birds, not in any other known taxon
(including alvarezsaurs).

Please people.....  Feathers do not define birds, ancestory does.  Feathers
do not diagnose birds either because none of the very close relatives of
_Archaeopteryx_ are found in any kind of sediment that would preserve
feathers (except for the probably non-avian _Mononykus_ :-)

So what do we have that is a good diagnostic character of the Avialae/Aves
clade?  Yes, that's right, loss of the cranial process of the pubic boot,
appearence of the proximodorsal process of the ischium, and distal migration
of the obturator process of the ischium.  Not feathers, not retroverted pubes
(which SVP showed us can be more than variable....), not kinetic skulls, not
tooth loss, not ferculae, not uncinate processes.  Just three simple pelvic

Please look things up in the archives to see if they've been discussed one or
five or twelve times before......   Also check out:

Novas, F E, and Puerta, P F.  1997.  New evidence concerning avian origins
from the Late Cretaceous of Patagonia.  Nature 387:390-392.

and for a bit of an easier read:

Buchholz, P.  1997.  _Unenlagia_: the half bird.  Dinosaur Discoveries 5:2.

And I'm not recommending that second one just because I wrote it.......  :-)

Peter Buchholz

I am Scuzzlebutt!  Lord of the mountain.  Behold!  My Patrick Duffy leg.