Dear Paleonet-ers
Let's turn the thermostat down a bit and closely examine John Jackson's rhetoric.
First up, JJ says:
JJ says: "Norell's insipid warm-over of his half-baked ideas"
OK, this tone could be a little more respectful. Mark Norell is a respected and highly qualified professional paleontologist who has examined a huge number of theropod fossils, including primitive birds and dromaeosaurs. You are welcome to criticize Norell's ideas, but ad hominem attacks don't help anyone.
To continue, JJ avers: "Czerkas is not the only person who believes Norell's use of cladistics is “one of the biggest mistakes ever made in paleontology”.
Czerkas may not be alone, but he is certainly part of a rapidly shrinking minority. Cladistics actually has a pretty darn good record when it comes to assessing dinosaur relationships. From Gauthier (1986) onwards, the phylogeny of theropods (including the relative position of the bird clade) has remained very stable; and many of the more "controversial" relationships posited by cladistic analyses have been verified by recent fossil discoveries. Remember when the notion that segnosaurs (therizinosauroids) were theropods was decried as cladist-generated rubbish? Now we have basal segnosaurs like _Falcarius_ that cement the relationship of segnosaurs within the Theropods. There are other examples, too numerous to mention.
It is also interesting to note (I think) that the most virulent opponents of cladistics have yet to come up with an alternative method for evaluating evolutionary relationships. There's a lot of heat from these folks, but not much light. What's your method, John?
JJ continues: "One assymmetrical feather doesn't prove powered flight, but a set of all-round
bodily attributes ideally suited to flight including perfect and very large thrust-producing primary
feathers as seen on some dromaeosaurs is best explained by an ability to fly."
So, fill me in here. What "all-round bodily attributes ideally suited to flight" to these dromaeosaurs have? These attributes have certainly escaped my attention. From my perspective, these aerial dromaeosaurs are even less equipped than _Archaeopteryx_ for powered flight. All you've mentioned is the feather arrangement and morphology, and not explained why large primary feathers MUST be used for thrust. You should be aware that large primaries also allow for improved maneuverability during passive aerial locomotion (e.g., parachuting or gliding).
AFAIK, nobody doubts that basal dromaeosaurs like _Microraptor_ (?=_Cryptovolans_) were capable of some form of aerial locomotion. But we cannot say whether this aerial locomotion took the form of parachuting, gliding, powered flight - or even a strategy that opportunistically employed two or more of these.
JJ goes on: "For example, birds are closely related to dinosaurs, but in all likelihood were neither a descendant nor a sister group."
What else is left?
"And although Czerkas is almost certainly right to say early dromaeosaurs flew,"
He is? Then let's see his evidence!
> and to dispute Norell's theory that dromaeosaurs were nonavian ancestors of birds, they
> probably were the ancestors of modern birds!)
Actually, as Norell himself points out in his letter, this is NOT what Norell or any other paleontologist is saying (see the letters, which you kindly include in your message). John, you have completely misunderstood their arguments. They are NOT saying that dromaeosaurs were the "ancestors" of birds. This is like saying that chimpanzees are the ancestors of humans. Paleontologists are saying that the clade Deinonychosauria(dromaeosaurs+troodontids) is the *sister group* of birds. If you cannot grasp the crucial difference between "ancestor" and "sister group", then you have no business editorializing on the evils of cladistics.
And to wrap this up, JJ tells us: "A sound and honest appraisal of the evidence supports few of Norell's claims, in particular that of having "an open mind".
I guess this "sound and honest appraisal" is in the eye of the beholder. I certainly do not see any compelling evidence that basal dromaeosaurs were capable of powered flight. I certainly believe that _Microraptor_ could climb trees and glide - but this is a long way from saying it was a powered flier. When it comes to the ecomorphology of domaeosaurs and basal birds, I believe Norell is infinitely closer to the mark than Czerkas, and I cannot think of one paleontologist who would believe differently.
Cheers
Tim
John Jackson <strangetruther@yahoo.com> wrote:
My contribution (which I am sure "Discover" will
undoubtedly print in their next edition) following on
from Norell's insipid warm-over of his half-baked
ideas, is as follows:
Czerkas is not the only person who believes Norell's
use of cladistics is “one of the biggest mistakes ever
made in paleontology”. One assymmetrical feather
doesn't prove powered flight, but a set of all-round
bodily attributes ideally suited to flight including
perfect and very large thrust-producing primary
feathers as seen on some dromaeosaurs is best
explained by an ability to fly. Perhaps the world's
most respected philosopher of biological science,
Elliott Sober, and probably the world's top expert in
cladistics, Joe Felsenstein, both agree Norell's
conclusions are unjustified. They would not agree
that cladistics is "an empirical method", and
they
would appreciate that just being used throughout
systematic biology doesn't mean it is always used
properly. They understand the role of cladistic
analysis in palaeontology better than Norell, and they
believe his use of simplistic cladistics is wrong
because dino-bird evolution was so complex. (For
example, birds are closely related to dinosaurs, but
in all likelihood were neither a descendant nor a
sister group. And although Czerkas is almost
certainly right to say early dromaeosaurs flew, and to
dispute Norell's theory that dromaeosaurs were
nonavian ancestors of birds, they probably were the
ancestors of modern birds!) A sound and honest
appraisal of the evidence supports few of Norell's
claims, in particular that of having "an open mind".
Original letters:
1:
For the record, the claim that dromaeosaurs “could not
fly” in June’s “The Dragons of Liaoning” is false. I
was the first to publish on
dromaeosaurs from Liaoning
having asymmetrical flight feathers on their hands,
which confirmed that these dromaeosaurs had actual
wings and the ability to fly. The paper describing the
fossils of these flying dromaeosaurs was one of
several regarding fossil birds and pterosaurs included
in The Dinosaur Museum Journal, Volume 1, August 1,
2002. For the past two decades, scientists using
cladistics have claimed that dromaeosaurs were
nonavian ancestors of birds, representing the best
examples of how ground-dwelling dinosaurs supposedly
evolved into birds. This has been one of the biggest
mistakes ever made in paleontology. Perpetuating this
mistake does a disservice to your readership.
Stephen Czerkas
Director, the Dinosaur Museum
Blanding, Utah
2:
It is not so easy to make a simple correlation between
asymmetrical feathers and flight. Many flightless
living birds display these feathers, but they are
only
one small part of a multipart flight apparatus. What
does Czerkas mean by flight? Is it powered flight as
in birds, gliding, or even parachuting? Asymmetrical
feathers may confer an aerodynamic advantage in any of
these, but whether the second two are necessarily
homologous to bird flight is a complex question. Where
are the data (like wind-tunnel or biomechanical
studies) that support his claim that these animals
were winged? Czerkas’s assertion that the use of
cladistics is “one of the biggest mistakes ever made
in paleontology” is laughable. Cladistics is an
empirical method that estimates genealogy and is used
throughout systematic biology. If Czerkas understood
cladistic analyses, he would realize that none of us
ever said that dromaeosaurs were the ancestors of
birds. Rather, the current hypothesis places
dromaeosaurs and troödontids together in a group that
shares a common ancestor with birds. Could some
basal
dromaeosaurs fly? I have an open mind, but I await
data and evidence rather than simplistic wing-waving.
Mark Norell, curator of paleontology, American Museum
of Natural History
Finally (me again) I forgot to say that Norell et al
wouldn't know evidence if they fell in a tub of it.
John V. Jackson
____________________________________________________
Start your day with Yahoo! - make it your home page
http://www.yahoo.com/r/hs
__________________________________________________
Do You Yahoo!?
Tired of spam? Yahoo! Mail has the best spam protection around
http://mail.yahoo.com