Message 2003-03-0001: RE: Note 9.4.1

Tue, 04 Mar 2003 23:41:55 +0100 (MET)

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Date: Tue, 04 Mar 2003 23:41:55 +0100 (MET)
From: David Marjanovic <>
Subject: RE: Note 9.4.1

> Node- and stem-based definitions are most certainly useful tools in
> taxonomy!  This is especially true for those of us who work in fossil
> forms and on large scale evolutionary biology issues.
> For example, complimentary stem-defined taxa have exactly the same time of
> origination *by definition*; in contrast, node-defined taxa within these
> stems could have radically different times of origins (as, similarly,
> would apomorphy-defined taxa within these stems).

To take another example, one that may have more relevance in practice:
Usually in an interesting fossil exactly the part with the defining apomorphy is
not preserved. In order not to take a stupid example like defining birds as
having feathers, I'll take a very interesting apomorphy (or 2) that dinosaurs
have: an asymmetric reduction of the hands, with fingers V and IV shrinking
considerably (IV losing 2 of its 5 bones) but III, II and even I not changing
or even growing. Nobody has, to my knowledge, tried to use it to define
Dinosauria so far, because the _three or four_ closest outgroups (as of end 2002)
don't preserve any hands whatsoever. (You see I'm talking of single specimens.
"This bone is the proof that there is a connection between the dwarf
brontosaurs and the giant brontosaurs", as a Disney comic put it.) We wouldn't be
able to tell if they are dinosaurs or not, driving a good proportion of popular
science book authors crazy, even though the phylogenetic positions of 3 of
them are pretty certain (at the moment).

Why would distance-based (isn't that phenetics?) phylogenies promote nodes &

>                 Thomas R. Holtz, Jr.
>                 Vertebrate Paleontologist
> [...]
>   -----Original Message-----
>   From: peter a. cejchan []
>   Sent: Tuesday, February 25, 2003 8:35 AM
>   To: PhyloCodeList
>   Subject: Note 9.4.1
>   Do we really need node- and stem-based definitions? Perhaps molecular
> phylogenies (seem to) force us to use these. However, adhering solely to
> apomorphy-based definitions would simplify Art. 13. Are there other cases
> for node- and stem-based d's than are the distance-based phylogenies? Just
> my opinion, as usually...
>   ++pac

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