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Re: The Two Principal Dinosaur Clades Defined



In a message dated 95-12-09 20:32:22 EST, longrich@phoenix.Princeton.EDU
(Nicholas R. Longrich) writes:

>       What's the consensus (or the arguments) on where sauropodomorphs 
>fit in? Are people pretty much agreed that they are closer to Iguanodon, 
>or if not, why not? 

Most people still see sauropodomorphs as closer to theropods than to
ornithischians, but the characters they cite in support of this can in all
cases also be viewed as plesiomorphies and convergences. When I finish
_Mesozoic Meanderings_ #2, I'll include the characters that I think support
descent of sauropods, prosauropods, segnosaurs, and ornithischians from a
common phytodinosaurian ancestor (a small [1-2 meters long], probably
arboreal herbivore with leaf-shaped teeth, a forwardly declined chin, large
eyes, 10 cervical vertebrae, 15 dorsal vertebrae, three sacral vertebrae of
which two are primitive for Dinosauria and the third is added from the tail,
dozens and dozens of caudal vertebrae, powerful manual digit I, pentadactyl
manus and pes, not quite fully erect hind limbs, perhaps pre-feathers, and a
double row of dorsal scutes).