Re: MY THOUGHTS ON THE 'DINO/BIRDS'

["Thomas R. Holtz, Jr." <th81@umail.umd.edu>]

At 09:02 PM 6/27/98 PDT, Matt Troutman wrote:

>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.  

However, he has not identified characters found in crocodylomorphs and basal
birds which are not also found in advanced nonavian coelurosaurs.
Furthermore, he has not yet shown a phylogenetic hypothesis explicitly
showing WHERE among the crocodylomorphs (even multiple possible different
origins) he would place the birds.  It would be appropriate to do so, so
that these hypotheses might be fairly tested.

><<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.

Well said!!

>These are the 
>characters that are not found in any dromaeosaur, oviraptorosaur, 
>troodontid, ornithomimid, or tyrannosaur but are found in Archaeopteryx 
>and later birds.

(Although a single sternal unit, one of the features listed, IS present in
Sinraptor and in Baryonyx.  Furthermore, Rahonavis demonstrates many of
these features, which is why I and others are puzzled when Martin has
claimed that this animal is non-avian.).

>Flight characters may not just evolve for flight.  
>Climbing and arboreality can account for the flight chartacters.  

Or, I might add, particular modes of predation.  Not so say any two or more
of these are mutally exclusive behaviors!


>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.

Or, to be fair, that dromaeosaurs are more closely related to neornithines
than was Archaeopteryx.  (Dromaeosaurs are certainly more advanced than
Archaeopteryx in the features which make them dromaeosaurs: the development
of their peculiar tail adaptations, the size and shape of pedal digit II, etc.).

"Bird" does not equal "advanced" among theropods anymore than "horse" equals
"advanced" among mammals: both birds and horses represent particularly
highly specialized clades among their respective groups, but non-avian
theropods and non-equine mammals had plenty of their own specializations in
their own lineages.

>The 
>retention of the ascending process of the jugal, the 
>squamosal-quadratojugal contact, the serrated teeth,

Juvenile dromaeosaurs do not have serrated teeth, and some dromaeosaurs have
a "pinched" or "waisted" toothed form.

>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 
>Archaeopteryx.  
>
As a proud papa, I'd like to remind people that birds ARE maniraptoriforms
*by definition* (i.e., Maniraptoriformes is defined as all descendants of
the most recent common ancestor of Ornithomimus and Neornithes).

On the other hand, I agree with the main point of this statement.  Until
such time as particular derived characters can be found in dromaeosaurs and
birds more advanced than Archaeopteryx, but not in Archie itself; and that
the most parsimonious distribution of these data supports the hypothesis
that dromaeosaurs share a more recent common ancestor with neornithines than
with Archaeopteryx; then we must provisionally go with the hypothesis
currently supported by the data: namely, dromaeosaurs + (Archie + later birds).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661