Message 2001-06-0117: Crown groups

Sun, 17 Jun 2001 16:34:34 +0200

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Date: Sun, 17 Jun 2001 16:34:34 +0200
From: David Marjanovic <>
Subject: Crown groups

In (at least vertebrate) paleontology there is an ever-recurring problem --
how to apply classical names like Aves and Mammalia. One idea is to define
them as crown groups, i. e. as nodes that include all living members of the
traditional groups. This excludes basal members that have traditionally
always been considered members: e. g. *Archaeopteryx* and nearly all other
Mesozoic birds from Aves = (*Passer* [sparrow] + *Struthio* [ostrich]),
*Morganucodon*, *Megazostrodon*, *Sinoconodon* etc. from Mammalia =
(placentals + marsupials + monotremes), *Proterosuchus*, *Archosaurus* etc.
from Archosauria = (*Crocodylus* + *Passer*).

Currently the crown-group definitions of the mentioned taxa have priority;
however, many paleontologists simply reject their usage and often the whole
crown-group concept. No consensus is in sight. The implementation of the
PhyloCode will reset all priority to zero, and these fights will intensify.
The current draft of the PhyloCode has no opinion on this, except
Recommendation 10A, which is inapplicable -- usage is approximately the same
for both methods.

Should the PhyloCode have an opinion about this, and if, which one?


Feedback to <> is welcome!