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Re: Dinosaurs and birds
T. Michael Keesey writes:
> > But that's about it. I have trouble believing that the first
> > sauropods lived in trees, or even the first tyrannosaurs. Then
> > again, as Mike Taylor says, "I have a hard time believing" is not
> > admissable evidence. :-)
> True, and I think his case would be more for the first
> sauropodomorphs being arboreal, which is slightly easier to imagine
> (although still not backed by any evidence). (Then again, I seem to
> recall him doubting the monophyly of Sauropodomorpha, but I'll
> leave that alone for now.)
For avoidance of doubt: "his" and "him" here still refer to George
Olshevsky, not to me!
Regarding the monophyly of Saurpodomorpha (i.e. sauropods being either
descended from or sister group to prosauropods): I don't think anyone
has seriously doubted it since the days of Huene, although the precise
arrangement of basal taxa within Sauropodomorpha is still very much up
for grabs -- see for example Upchurch's and Yates's papers in the
recent _Special Papers_ volume.
Olshevsky's (1991) idea was not that sauropods were polyphyletic, but
that segnosaurus (therizinosaurus) were derived prosauropods -- an
idea that had other supporters back then, but which has subsequently
been thoroughly overturned by the discovery of more basal
therizinosaurus which show them to be coelurosaurs. (I know you know
all this, Mike, it's for the benefit of the original questioner :-)
For this reason, Olshevsky proposed the name Brontosauria for a group
uniting Sauropodomopha with Segnosauria, but thankfully this name has
not been used much (in fact, at all, so far as I can tell). In this
formulation, Sauropodomorpha would be paraphyletic, which I guess may
be what Mike (Keesey) was referring to. But AFAIK George has never
proposed separate origins for sauropods and prosauropods.
Regarding sauropodomorph origins: there is no reason at all to suppose
an arboreal lifestyle for the earliest and most basal known members.
Rather, it seems clear that they were aquatic.
Oops ... three days late. Sorry.
/o ) \/ Mike Taylor <firstname.lastname@example.org> http://www.miketaylor.org.uk
)_v__/\ "Leopards break into the temple and drink the sacrifical chalices
dry; this occurs repeatedly, again and again: finally it can be
reckoned upon beforehand and becomes a part of the ceremony" --