Re: thanks and a note about _Alxasaurus_

[Dinogeorge@aol.com]

In a message dated 2/2/99 1:14:24 AM EST, qilongia@yahoo.com writes:

<< Therizinosauroids, dromaeosaurs, and basal birds are opisthopubic,
 oviraptorosaurs are propubic. There are two equally parsimonious
 explanations for this distribution: EITHER opisthopuby evolved in the
 common ancestor of all these, and oviraptorosaurs reverted to propuby;
 OR the common ancestor of all these was propubic and opisthopuby
 evolved separately in theriz.s and dromaeosaurs+birds. Each requires
 two evolutionary steps. Additional, more complicated scenarios are
 possible, but require additional evolutionary steps for which there is
 no evidence at present.> >>

Opisthopubic pelvis in segnosaurs has nothing to do with opisthopubic pelves
in theropods; it's derived from an intermediate condition between the propubic
pelvis in prosauropods and opisthopubic pelvis in ornithischians. Once it is
understood that segnosaurs are >not< theropods but are derived from lineage
linking prosauropods with ornithischians, the mystery surrounding their
opisthopubic pelves (and prosauropod-like feet) evaporates. If you imagine
that segnosaur opisthopubic condition is homologous with, say, opisthopubic
condition in velociraptorines and birds, you must then also explain why
segnosaurs share so few other features with these taxa.