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In a message dated 95-12-14 13:41:38 EST, martz@holly.ColoState.EDU (Jeffrey
> They list the
>following dinosaurian synapomorphies for Herrerasaurus: "absence of the
>prefrontal...extension of the abductor musculature onto the frontal,
>lateral exposure of the quadrate head, and a reduction of the
>posttemporal opening to a foramen...addition of the dorsal vertebrae to
>the sacrum, an elongate deltopectoral crest on the humerus, loss of ungal
>on the fourth digit of the hand, a brevis fossa on the illium, a
>subrectangular femoral head, a cnemial crest on the tibia, and an
>ascending process on the astragalus." Science, p. 1138)
Right off the bat, "addition of the dorsal vertebrae to the sacrum" is a
character absent from most (though not all) prosauropod dinosaurs.
Prosauropods generally had three sacrals: the two primitive for Dinosauria
plus one more taken up from the tail. (This gave prosauropod ilia their
characteristic "backward tilt.") So that's _not_ a dinosaur synapomorphy
unless you believe most prosauropods _lost_ a sacral to the dorsal series
(far-fetched but not as impossible as reacquiring a lost pedal digit).
Melanorosaurids (which I think were not prosauropods but very primitive
sauropods), _Massospondylus_, and the undescribed _Roccosaurus tetrasacralis_
(possibly a melanorosaurid) gained one additional sacral from the dorsal
series for a sacral count of four.