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Re: Sauropod ancestry?
In a message dated 7/18/00 7:37:09 PM EST, firstname.lastname@example.org 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).