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

RE: Two "new" papers and a query for Thomas Holtz

--- "Williams, Tim" <TiJaWi@agron.iastate.edu> wrote:
> Thomas Holtz wrote:
> > Quite so!!  As I stated in my review, the Czerkas
> et al. papers suffer
> > from a very typological mode of systematics rather
> than a phylogenetic 
> > one 
> The Czerkas papers have achieved something quite
> rare in the annals of
> paleontology: the proposed phylogeny has the
> potential to be offensive to
> both those who favor the origin of birds from
> theropods, and the BAND/ABSRD
> camp.  Czerkas et al. hold that dromaeosaurids are
> not true theropod
> dinosaurs, but secondarily flightless birds; and
> that birds and dromies (and
> _Scansoriopteryx_) share a "pre-theropodan" origin. 
> The similarities
> between dromies and "true" theropods is attributed
> to convergence.  No, I'm
> not making this up.
> The volume features some superb illustrations,
> though.  (Except, maybe, the
> model of _Deinonychus_ on p.98, which looks like Big
> Bird's evil cousin.)
> Tim
BRIEF RESPONSE: "secondarily flightless birds" and
"true theropods" are -- let me be diplomatic -- a
combination of alliterations without  links to
phylogenies. A "secondarily flightless bird" IS a
theropod dinosaur secondarily flightless, because ALL
"birds" are theropod dinosaurs. I have yet, in 47
years of being enveloped in these taxa, to encounter a
"true" theropod. Stephen Czerkas's taxa are
fascinating, but I do not believe an elongate manus
digit III (the primary definition of the taxon itself)
on a secondarily flightless dinosaur (although, since
it is a nestling, how does one know Scansoriopteryx's
flight capabilities?), makes it a non-theropod or a
non-dinosaur. In all respects,  Scansoriopteryx is a
dinosaur, not a remote non-dinosaur outgroup, not a
sister taxon to a pterosaur, or an aetosaur, or a
phytosaur, etc., etc. (why Stephen uses "thecodont" is
beyond me, I'm afraid; the word has no scientific
meaning), but is a non-ornithischian dinosaur, i.e., a
saurischian.It is not a sauropod, nor "prosauropod"
(whatever that means), nor a Patagonian Triassic
taxon...and remains a secondarily flightless theropod.
 The "numerous primitive characters" Stephen insists
are there -- allegedly making it "a saurischian of
'pre-theropod' status, instead of a true theropod" --
I do not discern: the specimen itself is judged to be
a 2-3 week old nestling, and, like Kierkegaard,
Stephen is asking one to make a "leap of faith", as he
says the "primitive characters" presumably "were
retained throughout the life of the animal. Query:
what characters?          Only the discovery of a
fully mature specimen may resolve this issue". Indeed.
A subadult or adult specimen might render the nestling
meaningless; he calls it a "juvenile", I would iterate
it is a "baby", a 2-3 week old dinosaur, and I would
honestly hesitate, if I had been Stephen, to give the
animal a name (it is akin to attempting to diagnosis a
sauropod on the basis of an embryo, e.g.). What I am
attempting to say, I suppose: to remove a nestling
from Theropoda on the basis of a long digit is...not
especially parsimonious. Why? Because I have NEVER, in
47 years (oh, how I wish Sam Welles were alive to
contribute here) seen a diagnosis predicated upon so
many "ifs". I have never seen Theropoda defined as
taxa being unable to climb or fly, and I am a heretic,
I suppose, in thinking that there are ORIGINS of
flight among theropods, not an ORIGIN, different
lineages taking to the air, or jumping from trees
(after having run/climbed up them, because I have not
seen evidence of generations of small dinosaurs
spending their entire lives in trees without coming
One final comment in this diatribe: Stephen states
"While neither fully volant or strictly terrestrial in
its habits, Scansoriopteryx appears to represent the
arboreal 'Proavian' stage of bird origins of which
Heilmann (1927), Abel (1911) and Osborn (1900)
speculated upon so long ago". How does he know on the
basis of an animal which had only hatched 2-3 weeks
earlier? With no other known specimens, how can
Stephen claim that any of this, and that it is a
"proto-maniraptoran", and that the nestling supports
the idea that "birds" came "from the trees down", or
that "The cursorial theory has maintained that all
theropods, including maniraptorans were strictly
terrestrial"? I have NEVER seen Theropoda diagnosed on
this criteria in any of the primary literature since
Ostrom's work in the 1970s, nor in Jacques Gauthier's
pioneering 1984/1986 cladistic analyses.
I think Stephen's baby dinosaur is quite fascinating,
just as his Cryptovolans is a dinosaur (although I am
not sure what he means -- since he does not specify --
by "primary flight feathers"). On page 70 he uses
Archosauria Saurischia Maniraptora
Scansoriopterygidae, on page 101 it is now Aves
Maniraptora Dromaeosauridae. I'm afraid he has
misplaced the converted clade name Aves, and should
have used, I presume, Dinosauria instead of
Archosauria, and the phylogeny on page 120 is
incorrect. I agree with Greg Paul some dromaeosaurs
could fly, but the discussions on pp. 120-122 are not
I apologize, Tim, for the lengthiness of this, perhaps
not warranted. But the thoughts, like children, were
clammering for birthing.

Do you Yahoo!?
New DSL Internet Access from SBC & Yahoo!