Re: "Common ancestor" in cladistics

[Nick Pharris <npharris@umich.edu>]

Quoting Phil Bigelow <bigelowp@juno.com>:

> Depending on how one defines the informal group "fish", your students may
> have a right to balk.  If you mean that we had an ancestor that was a
> member of the clade [Pices + Chondrichthes], then I would think not.  But
> I've been wrong before.
>
> Aren't  "fish" paraphyletic??

"Pisces", as traditionally used--including chondrichthyans, ray-finned and
lobe-finned fishes, and often lampreys and hagfish for good measure--is
paraphyletic, yes.

And yes, we are most definitely part of the clade arising from the common
ancestor of chondrichthyans and other "fish".

Nick Pharris
Department of Linguistics
University of Michigan