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Thoughts on the new Czerkas book (long)
Got my copy of it last night. A very nice volume: excellent illustrations
and (especially) photographs. Very surprising in terms of the published
format: with the glossy pages, dust slip (complete with "questions answered
in this book" on the back), hard cover, and larger print it is visually more
like a general audience coffee table or a top-of-the-line "kid's book" (like
Thom Holmes recent series) in format than it is a serious scientific
journal. However, if kids pick this up they will be disappointed: this is
clearly a scientific text in content.
However, I have issue with some of the science. In general the anatomical
descriptions seem right on target (with a few, perhaps, that I question).
However, it is in the interpretation that I have some issue.
I'll post my notes taxon by taxon, and limit it to the dinosaurs (however, I
agree with Tracy: Pterorhynchus might be a reasonable sister taxon to
I) Archaeovolans: no real issues here. Apparently they only heard about
Yanornis after the paper had been submitted, so they were naming
Archaeovolans in good faith.
II) Scansoriopteryx (likely = Epidendronosaurus: they might be from the same
time unit, as the stratigraphy of the newly discovered Daohugou locality is
questionable): okay, having seen this guy, I agree that the identification
of the various parts of Epidendronosaurus were correct. Scansoriopteryx's
mandible is highly reminiscent of oviraptorosaurs in terms of the region
around the external mandibular fenestra; tail is more like eumaniraptorans
in details of the centra size and shapes.
The "Discussion" is where the science gets iffy. A quote (p. 85):
"However, this terminology [i.e., calling Scansoriopteryx an
theropod"] is an apparent contradiction in terms as according to definition,
"theropods" do not climb. Also, according to Gauthier (1986), theropods are
united as a group by having the second digit of the manus as being the
longest. Since the third digit in the manus of Scansoriopteryx is much
longer than the second, it must either represent a highly derived
specialization from that of typical theropods, or must represent a
pre-theropod status. The combination of the third digit having a more
elongate and robust third metacarpal; together with phalanges that become
progressively shorter distally, as well as the numerous primitive
characteristics throughout the body collectively suggest that these are not
aberrant reversals but reflect true plesiomorphic conditions. Therefore,
Scansoriopteryx is more parsimoniously regarded as being a saurischian of
"pre-theropod" status, instead of as a true theropod".
Spurious thinking involved here, and especially typological rather than
evolutionary thinking! To take it from the top:
a) Theropods (or "theropods" or whatever punctuation you put around
are not prohibited from climbing by definition!!! That was a remarkably odd
b) In Gauthier's (and other) analyses, Theropoda or Neotheropoda are
united by a second digit as the longest. However, like any trait, such
characteristics can and are modified by subsequent evolution within members
of that clade. Snakes and caecilians and whales are not excluded from
Tetrapoda for lacking the full compliment of limbs!! Or, sticking within
the same clade and character state, Alvarezsauridae is not excluded from
Theropoda even though its second digit is not the longest.
c) The elongate and robust third metacarpal occurs in other specialized
theropods (e.g., ornithomimids), which are not then eliminated from
d) What "progressive shortening of the phalanges distally"? They seem
subequal in digit III, and digits II and I show typical maniraptoran
e) What "numerous primitive features"? None are documented as such, and
indeed most of the anatomical details are described by the authors as
considered similar to Archaeopteryx, Sinornithoides, maniraptorans in
general, Compsognathus, or birds.
f) Consequently, the authors have absolutely no support for their
of a pre-theropod status of this taxon.
I am going to be interested in seeing where it DOES fall out, though!
Also, the authors once again conflate the "cursorial therory" of the origins
of bird flight with the "theropod position of birds"; as some of us have had
to say again and again and again, the two are NOT synonymous, and there
these authors even quote Chatterjee (who explicitly describes an arboreal
theropod origin) on numerous occasions.
Cryptovolans: The type specimen was previously described in Nature (Norell
et al. 2002 Nature 416: 36-37; see DML archives at
http://www.cmnh.org/dinoarch/2002Mar/msg00268.html). Oddly, both slab and
counterslab are listed in Czerkas et al. as being at the Liaoning
Paleontological Museum (LPM), but by Norell et al. at tehe Beipiao Museum
(BP); maybe two different names (and codes? annoying!!) for the same
insititution. A second specimen is also described.
Czerkas et al. correct some anatomical errors in Norell et al.'s
description: I agree with some of their corrections, but disagree with
others. The new description clearly demonstrates a fused sternum in this
form (contra Norell et al.). Czerkas et al. demonstrate the presence of
some long feathers on the forelimbs. I disagree with their idea that the
long feathers near the legs are unquestionably NOT attached to the leg: the
base of all these long feathers, where preseverd, are fully consistent with
this critter having long leg plumage. (I think that this is a case of the
authors being 'the pot that called the kettle black'; they accuse Norell et
al. of not seeing things that are their due to preconceptions, yet they
themselves miss this anatomical detail (figured on Fig. 11) due to their
own). One can falsify me by demonstrating that these feathers extend
anterior to the tibia and fibula.
Once again, typological thinking shows up in their description, but such
statements as "By definition, the fingers of all theropods have reduced
proximal phalanges and elongated penultimate phalanges" (p. 110) (in this
case, they show that ph. I of digit III is longer than any other non-ungual
phalanx in that digit, as in Sinornithosaurus). Throughout they confuse (or
are at least do not clearly distinguish) 'sister taxon', 'ancestor', and
'precursor'. They accuse cladists of requiring non-flying dromaeosaurs
(incidentally, don't recall anyone ever coding "Character XXX: 0,
non-volant; 1, volant" in a matrix!!). Consequently, they misunderstand
cladistic methodology, leading to statements like (pp. 119-120):
"Not acknowledging that there is such a strong tendancy towards
flightlessness among birds has remained a major flaw in the current
methodology of cladistics which does not sufficiently account for such
reversals. Without such considerations of terrestrial forms possibily being
secondarily flightless, no method of phylogenetic analysis can present an
accurate interpretation of avian relationships. Not only has this failed to
have been properly employed, but by not doing so, cladistics has presented a
highly misleading interpretation of the evidence by arbitrarily insisting
that the ancestral origins of avian flight must have been from an
exclusively ground dwelling theropod dinosaurs. Since dromaeosaurs can no
longer be regarded as terrestrial precursors of birds, using them as the
evolutionary link between dinosaurs and birds in the manner that cladists
have proposed is shown to be invalid."
Yikes! Not quite as many errors per sentence as some papers on bird
origins I've read, but getting up there!
(Among other things, would someone please demonstrate how an analysis
(especially genus/species level one like the AMNH ones, Mickey's, Jaime's,
or my forthcoming ones) PREVENTS the recovery of secondarily flightless
dromaeosaurs? Such a demonstration would not be "but that's not the answer
you get", because not one us knows the True Answer (tm). The demonstration
would have to be showing how the analysis could not, under any circumstance,
yeild dromaeosaurs nested within known volant forms.)
The discussion on p. 120-122 is riddled with misunderstanding of cladistic
taxonomic methodology (not in this case the analytical techniques, but the
naming of names). Additionally, so that others might learn from this
example: if you want your professional published scientific work to be taken
seriously, it is generally best to refrain from the use of terms like
"politically correct" (which, incidentally, has such a dated early 1990s
sound to it: might as well throw in a "groovy" and "daddy-o" to keep the
terminology current... ;-S) and "dogma". Scientific discussions work best
when soberly and clearly put forth, at least in my opinion.
And the biggy: is this thing a flier? I have no problem per se with volant
dromaeosaurs. However, how does one demonstate it? You can't just pick up
the specimen and toss it to see if it flies: if it does, then trilobites
were also volant! ;-) Mere presence of feathers, even large ones on the
arms, might be necessary but not sufficient. My (admittedly quick)
measurements of the best preserved feathers they show (i.e., ones where the
shaft and the edges are both clearly present) finds an asymmetry of only 0.9
at best: they assert these feathers are asymmetrical but do not show
measurements to back up their case. Fully powered flight would require
sufficient mobility at the shoulders, in the arms, etc.: that MIGHT be
possible, especially in basal deinonychosaurs. Still, the case is far from
established, and the use of conditional words like "may" or "possibly" would
actually strenghthen their case.
Omnivoropteryx: An extremely cool animal: can't wait to see more details on
it. Skull similar to Caudipteryx (although unfortunately that is mostly
profile: would like to see this thing either prepped out or (better yet) 3-D
CAT scanned to get a handle on the various sutures between the skull bones.
Postcranium is similar to Sapeornis (for which, as they point out, the skull
is not known). They attempt to distinguish the two by body proportions, but
unfortunately use the dubious method of rescaling Omnivoropteryx to the same
femur length as Sapeornis. To demonstrate the fallaciousness of this idea,
imagine taking a 9 year old boy, measuring his limb bones, scaling the
measurements up so that the femur was the same as that of an adult man, and
then using the differences between the rest of the rescaled limb
measurements to demonstrate that the boy and the man are different taxa...
Yes, others have done what they are doing in the past, but that doesn't mean
that they were justified in so doing.
A final note on peer-review: There is nothing in the above comments that
couldn't have been corrected by serious peer review. It's not a perfect way
of doing things: errors (both technical and philosophical) can and do still
make it through. However, there is a better chance that some of these
aspects *might* be caught and modified so that the paper as a whole stands
better in the end. Does that mean that you might not wind up saying exactly
what you wanted to say to begin with? Sure. However, this MIGHT be because
your reviewer caught some logical flaw in your arguement or some
less-than-professional comment in your text: are these bad things?
Thomas R. Holtz, Jr.
Department of Geology Director, Earth, Life & Time Program
University of Maryland College Park Scholars
College Park, MD 20742
Phone: 301-405-4084 Email: firstname.lastname@example.org
Fax (Geol): 301-314-9661 Fax (CPS-ELT): 301-405-0796