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Re: Sauropod ancestry?



In a message dated 7/18/00 7:37:09 PM EST, tmk@dinosauricon.com writes:

<<  Didn't some icthyosaurs re-evolve the sixth, seventh and eigth digit? >>

These are scarcely digits in ichthyosaurs; more like collections of 
supernumerary phalanges. As far as evolving new structures goes, euhelopodid 
sauropods seem to have evolved five or more new cervical vertebrae (rather 
than, as in diplodocids, taking them into the neck from the back). The 
evolution of new or supernumerary structures does happen among tetrapods, but 
it's quite rare--and I've yet to read about a genuine instance where a 
complete manual or pedal digit, with phalanges and ungual, is reevolved 
within a lineage (as opposed to hyperdactyly, which is a pathological 
condition that can afflict individuals within a species).