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Re: WHAT are segnosaurs?



Ken Kinman wrote-

>       What I envision is therizinosaurs as stem tetanurans (perhaps small
> unknown primitive forms being stem neotheropods), and eventually grading
> into primitive coelurosaurs and even primitive bullatosaurs (ornithomimids
> and troodontids).
>        Therefore instead of comparing therizinosaurs to prosauropods, it
> might be more interesting to compare them to Guaibasuarids, Coelophysids,
> Sinraptorids, and/or basal coelurosaurs such as Ornitholestes.  I suspect
> that Beipaiosaurus may be a rather advanced therizinosaurian (whether the
> latter is a paraphyletic group or polyphyletic).
>       If therizinosaurs (as now envisioned) are actually polyphyletic or
> even highly paraphyletic, splitting them into a number of separate OTUs
may
> become necessary (but then the fragmentary nature of most forms would
become
> extremely problematic).  But I would especially like to see some concerted
> attempts to compare various therizinosaurians particularly with sinraptors
> and primitive coelurosaurs (as opposed to prosauropods which are probably
> more primitive).

How can therizinosaurs "start as stem tetanurines, then grade into basal
coelurosaurs or bullatosaurs"?  Coelurosauria is not a level of advancement
or similarity, it's a phylogenetic group.  Therizinosaurs cannot start as
non-coelurosaurs and grade into coelurosaurs unless they are the
paraphyletic grade that forms the backbone of the tetanurine tree (which is
ridiculous).
In any case, several studies have already compared therizinosaurs with
non-coelurosaurs.  For instance, both Holtz (2000) and Rauhut (2000) have
therizinosaurs along with basal coelurosaurs, carnosaurs, ceratosaurs,
herrerasaurids, etc..  It's been done and they still clade with
oviraptorosaurs.  Incidentally, Xu et al. (1999) has Beipiaosaurus,
Alxasaurus and Therizinosauridae as separate OTU's, as I'm doing with the
prosauropod experiment.

Mickey Mortimer