Re: Dinosaurs with Pygostyles

["Mickey Mortimer" <mickey_mortimer@email.msn.com>]

Nick Longrich wrote-


In a number of ways
>oviraptorosaurs are less birdlike than dromaeosaurs- the sternum is
>shorter, they haven't completely lost the anterior portion of the pubic
>boot, the transverse processes in the anterior tail are placed fairly
>dorsal, the posterior tip of the ilium lacks the typical pointiness seen
>especially in archaeopteryx, rahonavis, modern birds, and somewhat in
>dromaeosaurs.

I agree.  Other characters shared by dromaeosaurids and Archaeopteryx
(though not neccessarily exclusive to that clade), but absent in
oviraptorids are:
- frontal nearly twice as long as parietal
- lateral temporal fenestra dorsoventrally shorter than orbit
- distal ends of paroccipital processes twisted to face posterodorsally
- reduced number of caudal vertebrae with transverse processes
- proximal caudal centra rectangular in section
- reduced number of elongate chevrons
- laterally directed glenoid
- slender third metacarpal
- manual ungual I smaller than manual ungual II
- opisthopubic pelvis
- ischium reduced in length
- obturator process placed distally
- prominant posterior trochantor
- sickle claw

> But in a number of other ways they are disturbingly advanced. The
>separated acromion, the shortening of the distal tail, the fan instead of
>frond in the tailfeathers. And of course that pygostyle. There appears to
>be a lot of convergence and reversal and I'm not sure where they all
happen.


What do you mean by "shortening of distal tail"?  Archaeopteryx and
Rahonavis have very elongate distal caudal vertebrae compared to other
coelurosaurs, especially oviraptorids.  The separated acromion also occurs
in Sinornithosaurus, which many believe is a dromaeosaurid.  The pygostyle
is only known in the one form, not in three oviraptorids or Caudipteryx,
which (if the pygo ovi is identified correctly in the new article as a
caenagnathid) surround the pygostyled species phylogenetically (Caudi
(Caenag+Ovirap)) and point to convergence.

How many studies actually *test* whether dromaeosaurs and
>oviraptorosaurs are inside an Archaeopteryx+modern birds clade?  Gauthier
>1986? Nope. Holtz 1994? Nope. Makovicky and Sues 1998? Nope. Sereno 1999?
>Forster et al (1998) and Novas' works are the only ones that actually allow
>for the possibility. What is generally done is to either code only
>Archaeopteryx, or to assume that Archaeopteryx and modern birds form a
>clade exclusive of everybody else. This is not testing hypotheses of avian
>evolution, it is assuming them.

Just for the record, in my analyses I do test for paraphyly in Aves.  I use
Archaeopteryx, confuciusornithids, enantiornithines, Patagopteryx and
ornithurines as separate OTU's.  As an interesting note, in a preliminary
analysis I didn't add any of the characters that are normally used to
support the ornithothoraces (enants+ornithurines) and they still came out as
sister groups (confuciusornithids and Patagopteryx weren't added yet).
Also, I recall Tom saying something in the past involving
confuciusornithids' placement in one of his newest phylogenetic analyses, so
at least he must also treat various birds as OTU's.  As far as I know, all
of his cladograms also come out with Aves monophyletic.

Mickey Mortimer