[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]


Peter Buchholz (whose name I misspell nearly every week) wrote:

>There are in fact three very subtle characters present in _Archaeopteryx_
>that clade it closer to modern birds than either is to dromaeosaurs.  They

>1) loss of the cranial process of the pubic boot making it look like a J in
>lateral profile.  This feature is also found in "Linsterosaurus", the flying
>raptor, _Adasaurus_, _Unenlagia_ and modern birds.  It is not found in other
>tetanuran theropods including dromaeosaurs or alvarezsaurs.
        Are you sure? Last time I looked, I thought several non-avian
coelurosaurs had rather j-like pubes... I think GSP restored _Compognathus_
with one. I also cannot recall any modern birds with a j-like pubis offhand,
but then, I ain't no avian neontologist. :)

>2) appearence of the proximodorsal process of the ischium (incidentally, a
>defining feature of the clade Saurirae, thus indicating it is probably
        Don't even bother *trying* to use Hou, Martin, Zhou and Feduccia's
1996 paper. The "cladistics" in it are beyond poor.
        If I interpret the data correctly (and I'm not so sure I do), this
process is what eventually fuses to the ilium, producing the fenestra seen
in modern birds. Just so everyone knows, those authors miscode that
character, presuming (a priori) that the unfused version is non-homologous
to the fused version. They establish two characters (22 and 32 in their data
matrix, which does not use the same numbering system as the cladogram
presented in the paper) based on the presence of the unfused process. This
contributes to the erroneous results of their study.
        Character 22, presence of the process, is coded as 0 for all birds
with the illia and ischia fused. Character 32, size of the "fenestra" formed
by the process, the shaft of the ischium, and the illium, is rather poorly
defined, and the polarity is doubtful. It is hard to concieve of how this
fenestra could have been small before it became large, as its size is in
part determined by the degree of retroversion of the ischium.
        However, the coding of these characters conveniently results in the
(demonstrably paraphyletic) grouping seen on their cladogram.
        (Just so Charger knows, Chatterjee believes that this fenestra is
present in _Protoavis_).

>3) distal migration of the obturator porcess of the ischium.  This feature is
>seen only in _Archaeopteryx_ and modern birds, not in any other known taxon
>(including alvarezsaurs).
        1. Isn't the *presence* of an obturator process in _Archaeopteryx_
        2. The obturator process is certainly distally placed in
dromaeosaurs, a therizinosaur, an oviraptorsaur, and perhaps a troodontid (?).
        3. If you mean what I think you mean on archaey, yeah, that would be
an *extremely* distally placed obturator process, but could you ref. this
(at least with some good pics so I know what you mean).

>Please people.....  Feathers do not define birds, ancestory does.

>So what do we have that is a good diagnostic character of the Avialae/Aves
>clade?  Yes, that's right, loss of the cranial process of the pubic boot,
>appearence of the proximodorsal process of the ischium, and distal migration
>of the obturator process of the ischium.
        First is rejected pending evidence (and is present in non-avian
_Unenlagia_), second is pretty good (but also present in _Unenlagia_), third
needs some justification.

>not kinetic skulls,
        Streptostylic quadrate? Chatterjee thinks so...

>not uncinate processes.
        *Ossified* uncinate processes might diagnose a more inclusive clade...

>Just three simple pelvic characteristics.
        Pelves rule!
    Jonathan R. Wagner, Dept. of Geosciences, TTU, Lubbock, TX 79409-1053
        "Chimp here does the killing." - Doug Mackenzie