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Re: Synapsids are NOT reptiles!



In a message dated 95-12-13 19:10:36 EST, martz@holly.ColoState.EDU (Jeffrey
Martz) writes:

> I would think that unless those marine and freshwater 
>critters that led to tetrapods was an example of amazing covergant 
>evolution starting with those basal vertebrates, you would have to say 
>we are descended from fish.

Since cladistic taxonomy is done on the basis of descent rather than
evolutionary novelty, the cladist can take one of _only_ two positions on the
relationship between tetrapods and fish. (1) If "fish" is defined broadly,
then it must take in all of Tetrapoda, and all tetrapods _are_ fish that
simply adapted to life on land. (2) If "fish" is defined narrowly (to include
only extant bony fish, for example), then tetrapods are not fish, nor are
they descended from fish; rather, tetrapods and fish descended from a common
ancestor that (most likely) lived, swam, and breathed in the water very much
like extant fish do today.

The fact that the common fish-tetrapod ancestor would undoubtedly be called
and classified as a fish by any rational observer had the tetrapods never
evolved makes no difference to cladistic taxonomy. The dogma of monophyletic
taxa produces some pretty contorted neologisms.