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Brontosauria (was Re: Graves museum exhibits)
T. Mike Keesey wrote:
Since DinoGeorge's Brontosauria is essentially Prosauropoda + Sauropoda, I
have on the Dinosauricon cladistically translated it as a node containing
the stem-based groups Prosauropoda and Sauropoda (as defined by Wilson and
Sereno, respectively anchored by _Plateosaurus_ and _Saltasaurus_). Thus
Brontosauria would be a group containing advanced sauropodomorphs,
possibly excluding things like _Thecodontosaurus_.
Surprisingly, things like _Thecodontosaurus_ and _Anchisaurus_ may actually
be CLOSER to the origin of sauropods than the big "broad-footed"
prosauropods like _Plateosaurus_ and _Riojasaurus_. At least, that's what
Sereno and others have found recently. For example, the cervical vertebrae
of _Riojasaurus_ actually show very little elongation (a very
un-sauropodomorph character). If melanorosaurids (like _Riojasaurus_) were
obligate quadrupeds then this posture probably evolved in prosauropods
independently of the sauropods. Maybe more than once, judging from
_Blikanasaurus_'s curious (and extremely heavily-constructed) hindlimbs.
The trouble is too, with certain prosauropod specimens (maybe
_Thecodontosaurus_) is that their bipedalism may be a juvenile character.
Young prosauropods may be slender-footed and bipedal, adults more
broad-footed and quadrupedal. (This is also seen in _Tenontosaurus_ among
ornithischians - young'uns were a lot like dryosaurs in cursoriality, adults
more like iguanodontids.) Certain "primitive" characters seen in
_Thecodontosaurus_ may be juvenile traits. (Remember _Efraasia_...?) A
re-description of _Thecodontosaurus_ is apparently on the way (in _JVP_ I
think) which hopefully will sort all this out.
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