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Re: PhyloCode Discussion: Crowns, Panstems, and their Correspondence to each oth


Jaime Headden wrote:

  However, birds such as moa and elephant birds and dodos still belong to
the crown ratites or columbiforms/columbids, so this is not really that
much of a problem.

Actually, whether or not moas (Dinornithithidae+Anomalopterygidae) or elephant birds (Aepyornithidae) are crown ratites hinges on their position relative to extant ratites. It is not a 'given'. True, the molecular (mitochondrial) phylogeny of Cooper et al. (2001) put rheas (Rheidae) as the basal ratite group, and therefore moas and elephant birds are contained within the crown group. But I doubt if this study is the final word on ratite phylogeny. If alternative topologies put moas and/or elephant birds in a basal position relative to extant ratites (kiwis, ostriches, rheas, emus, cassowaries), then moas and/or elephant birds are no longer in the crown group. Under this scenario, moas and elephant birds would be excluded from Ratitae, if this is the crown group.

In this same sense, the extinct sandcoliids within Coliiformes do
not get to be crowns, but are still part of one.

I'm not sure I know what you mean. The crown group Coliiformes comprise only living mousebirds plus all descendents of the most recent common ancestor of living mousebirds. All modern coliiforms belong to two genera (_Colius_+_Urocolius_) in the family Coliidae. Thus the crown-group is limited to a subset of the family Coliidae (all descendents of the most recent common ancestor of _Colius_ and _Urocolius_). The fossil taxa _Selmes_ and Sancoleidae are outside of crown-grou (for phylogeny, see Mayr and Mourer-Chauvire, 2004; J. Vert. Paleont. 24: 366-372). The extinct taxa _Selmes_ and Sancoleidae do not get to be included in the crown group, but would be in the stem clade ("Pancoliiformes").



Tim

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