[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Paraphyly and sister taxa (was Re: AMARGASAURUS SATTLERI)



In a message dated 9/3/00 1:08:36 PM Pacific Daylight Time, 
jeffmartz@earthlink.net writes:

<< 1. The common ancestor is the same taxon as "A", in which case "A" is
 paraphyletic with regard to "B".
 2. The common ancestor is the same as "B", in which case "B" is paraphyletic
 with regard to "A".
 3.  The common ancestor is neither "A" or "B", in which case it is DOUBLY
 paraphyletic. >>

Not sure what you mean by (3) here.  Let's say "A" and "B" are stem-based 
sister taxa and that both are subgroups of node-based taxon "X", which 
includes both "A" and "B" and their common ancestor.  Then the common 
ancestor is a member of taxon "X" but is not a member of taxon "A" or taxon 
"B".  Where is the paraphyly here?

I guess we need to clarify what we mean by "common ancestor" here.  Are we 
talking about an individual?  A population?  A species?  A family?

Nick P.