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MY THOUGHTS ON THE 'DINO/BIRDS'
I have been gone for a few weeks so I am going to put this all in one
<<Andre Elzanowski argues that oviraptors and other theropods with
folding arms are closer to birds than Archaeopteryx, and that they are
Elzanowski has also argued that hesperornithids are the first neognathus
<<It is a fact that many Cretaceous theropods have flight related
characters (folding arms, large furcula), sometimes the flight related
characters are better developed than those of Archaeopteryx (large
sternal plates, ossified sternal ribs, ossified uncinate processes,
shorter tail, tail with pterosaur-like ossified rods).>>
Theses features are not as 'well-developed' as Archaeopteryx.
Archaeopteryx has more avian folding wings due to the shift of the
glenoid socket, a larger furcula with a more acute angle (not in
oviraptors), and a *single* sternal unit (contrasted to the two plated
design of dromaeosaurs). The ossified sternal ribs are not really
relevent to flight. The uncinate processes in dromaeosaurs are
secondary ossifications (not extentions of the thoracic ribs in
ornithurine birds). Archaeopteryx has a tail that is shorter and has
more closely compressed zygapophyses.
<<What are we to make of this? I argue that since the Cretaceous
theropods have both avian nonflight and flight related features not seen
in Archaeopteryx, that it is therefore very possible that they descended
from fliers more advanced, and closer to birds, than the urvogel.
Certainly it is a valid and strong hypothesis, at least as good as the
But you forget the clearly birdlike features of Archaeopteryx:
a) Loss of the ascending process of the jugal bar.
b) Loss of squamosal-quadratojugal contact.
c) Triangular, crocodilian-type teeth without serrations and ventral
d) Dorsally placed, prominent acrocoracoid process.
e) *Single* sternal unit.
f) Heart-shaped cuneiform (according to Martin but not to Rick
g) Dorsal ischial processes.
h) Reversed hallux (anisodactyl foot).
i) Caudal vertebrae number reduced to 25-26.
<<Tom suggested that I favor scenario over phylogentic based hypothesis.
Nyet! Moi strongly disfavors those who prefer scenario over phylogenetic
arguments. That is the methodology of Feduccia and Martin. I would never
argue that some dinosaurs were secondarily flightless unless they had a
number of avian characters not seen in Archaeopteryx. Both aspects of
the problem are crucial.>>
I would argue that Feduccia prefers scenario over phylogeny. larruy
Martin is more evenhanded and has come up with some really strong
evidence for his crocodylomorph hypothesis.
<<As for cladograms and parsimony. I suspect one reason cladograms tend
to plot Archaeopteryx closer to birds is because they do not include all
the relevant characters.>>
Are the features stated above irrelevent characters. These are the
characters that are not found in any dromaeosaur, oviraptorosaur,
troodontid, ornithomimid, or tyrannosaur but are found in Archaeopteryx
and later birds. Flight characters may not just evolve for flight.
Climbing and arboreality can account for the flight chartacters.
<< Also, avian flight characters that are lost along with flight can
bias the results. For example, flying Confuciusornis had a long,
strut-like, retroverted coracoid like that of modern flying birds. A
flightless ostrich has a shorter, broader, procumbent coracoid that
looks like that of a dinosaur. Yet the ostrich is phylogentically much
closer to modern flying birds. In losing flight, the ratite coracoid has
reverted to the dinosaur condition.>>
Lest us not forget that other features support the high position in Aves
that ratites have. Ratites show features that are more advanced than
Confuciusornis, while dromaeosaurs do not show characters that
*definitely* show that they are more advanced than Archaeopteryx. The
retention of the ascending process of the jugal, the
squamosal-quadratojugal contact, the serrated teeth, the *two* sternal
plates, and the dorsal ischial processes all suggest that dromaeosaurs
were more primitive than Archaeopteryx+later birds. These features are
*relevent* characters that do not support the hypothesis that
dromaeosaurs (and other maniraptoriforms) are higher up that
<<Likewise, it is possible that the seemingly less avian - compared to
Archaeopteryx - coracoids of say dromaeosaurs are actually secondarily
reversed to the dinosaur condition. Scored on a cladogram, it would plot
below the urvogel. But maybe its just secondarily flightless.>>
This ignores the features stated above.
<<So far those doing cladistic studies have completely ignored the
potential bias introduced by the possibility of early loss of flight.
Taking steps to negate the bias (by running the character analysis while
including and excluding flight related characters and seeing if there is
a difference) should be the norm.>>
The 'flight characters' in dromaeosaurs can be explained by clibing and
<<Yet there is little doubt that the closest relatives of Archaeopteryx
are dromaeosaurs, they share so many detailed features absent in other
There is little doubt that vultures are related to seriemas but they
went through a touraco clade to get there.
The features that dromaeosaurs share with Archaeopteryx are primitive
for Aves and so far nothing has shown that these are not present in
Caudipteryx. I do not deny the close relation between dromaeosaurs and
Archaeopteryx but Caudipteryx can be easily an offshoot of the
dromaeosaur 'eumaniraptoran' clade.
It was also mentioned that feathers "must have evolved for insulation"
(paraphrasing). From what I have seen so far, the feathers of
Protarchaeopteryx and Caudipteryx seem to be for aerodynamics. They
cannot be for steering during cursorial activities (as suggested by
Padian 1997) because of the drag involved. The aerodynamics were
probably gliding. Feathers can be seen in ectothermic animals because
vultures and kingfishers can raise their body temperature through
featherd skin (Ruben 1991), yet feathers keep in the heat (Ruben 1991).
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