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Re: Massospondylids (long)



> << For instance Plateosaurus has 25 presacrals and a caudosacral in the
> sacrum whereas Massospondylus and Lufengosaurus have 24 and a dorsosacral.
>>
>
> All very interesting observations; please publish a.s.a.p.! Meanwhile,
watch
> out for sexual dimorphism in sacral vertebral counts among prosauropods
(see
> Galton's recent paper on Sellosaurus, as I recall), although the above
seems
> to be a pretty big difference.

Peter M. Galton: Are *Spondylosoma* and *Staurikosaurus* (Santa Maria
Formation, Middle-Upper Triassic, Brazil) the oldest saurischian dinosaurs?
Paläontologische Zeitschrift 74 (3), 393 -- 423 (December 2000)

Discusses, among other things, why 2 and not 3 sacrals are basal for
dinosaurs, and announces what Galton thinks was going on in *Sellosaurus*:

"Note added in press

A reexamination this summer shows that in some sacra of the prosauropod
dinosaur *Sellosaurus gracilis* the third vertebra is a caudosacral (so
S1+S2+CS), in the others it is a dorsosacral (so DS+S1+S2), and no complete
sacrum consists of only two vertebrae (S1+S2) (GALTON in press).
Furthermore, a cladistic analysis shows that S1+S2+CS is the plesiomorphic
state for Prosauropoda (and Sauropodomorpha) and DS+S1+S2 is the derived
state that occurred more than once, as did apomorphic reversals to the
plesiomorphic condition (GALTON & UPCHURCH in press a, b). These changes
probably represent several homeotic transformations or 'frame shifts'
[hooray!!! :-( ], both anteriorly and posteriorly, that are dependent on the
autonomy during vertebral development of early morphogenesis (involving
segmentation genes) and the development of character identity (involving
homeotic genes). In *Sellosaurus gracilis* the frame shift from DS+S1+S2 to
S1+S2+CS appears to be occurring as an individual variation (GALTON in
press).

GALTON, P. M. In press. Prosauropod dinosaur *Sellosaurus gracilis* (Upper
Triassic, Germany): Three vertebrae sacra [?] in middle of a homeotic
transformation or "frame shift". Neues Jahrbuch für Geologie und
Paläontologie, Monatshefte 2000, Stuttgart.
[Has been published meanwhile, as something like "Sex, sacra, and
*Sellosaurus*, or why the character 'two sacral vertebrae' is plesiomorphic
for Dinosauria". I just can't find the paper :-( ]
GALTON, P. M. & UPCHURCH, P. In press a. Basal Sauropodomorpha -
Prosauropoda. -- (In:) WEISHAMPEL, D. B., DODSON, P. & OSMÓLSKA, H. (eds.)
The Dinosauria, Berkeley (University of California Press). (2nd. edn.).
GALTON, P. M. & UPCHURCH, P. In press b. Prosauropod dinosaurs: homeotic
transformations ("frame shifts") with third sacral as a caudosacral or a
dorsosacral. -- Journal of Vertebrate Paleontology 20 (3), Chicago."

Well, the latter should be released pretty soon! :-)