[Taxacom] Underlying synapomorphies

Torbjørn Ekrem Torbjorn.Ekrem at vm.ntnu.no
Thu Mar 5 02:18:58 CST 2009

I am not sure I understand your specific question here, but the idea is 
that if a proportion of unrelated members of a larger group show the 
plesiomorphic character alternative for a complex character (indicating 
multiple secondary reductions), the most parsimonious solution will be 
if the apomorphic character alternative is regarded as a underlying 
synapomorphy for the group as a whole. Thus - the potential of having 
the complex character is what counts. As far as I know it was intended 
to be used on closely related groups to ensure homologous structures. 
Underlying synapomorphies certainly are problematic to use as arguments 
in phylogenetic analyses a priori, although there are examples where 
using them as explanations a posteriori perhaps is not too bad (for 
instance the multiple development and loss of wings in stick insects, 
see Whiting et al. 2003, 

Also, some authors have argued that the plesiomorphic character 
alternative should be used when coding polymorphic characters for 
phylogenetic analysis (e.g. Kornet & Turner. 1999. Syst. biol. 48: 
365-379). Is this really different from accepting underlying synapomorphies?

For those intersted, here is the abstract of Sæther's 1979 work: 


Dr. Torbjørn Ekrem
Vitenskapsmuseet, NTNU		
Seksjon for naturhistorie	
7491 Trondheim			

Museum of Natural History and Archaeology
Norwegian University of Science and Technology
NO-7491 Trondheim, Norway

Tel: +47 73 59 78 12
Email: Torbjorn.Ekrem at vm.ntnu.no
Web: www.ntnu.no/~torbjoe

Bob Mesibov skrev:
> Can you tell us more? For example, could a cephalopod-and-vertebrate
> style of eye be regarded as an underlying synapomorphy in Gastropoda -
> unexpressed, but possible within the lineage including both cephalopods
> and vertebrates?

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