Sexual dimorphism in moas

["Tim Williams" <twilliams_alpha@hotmail.com>]

A sobering reminder of the perils of separating extinct flightless theropod 
species based on size:


Huynen, L. C.D. Millar, R.P. Scofield, and D.M. Lambert (2003).  Nuclear DNA 
sequences detect species limits in ancient moa.  Nature 425, 175 - 178.

"Ancient DNA studies have typically used multi-copy mitochondrial DNA 
sequences.  This is largely because single-locus nuclear genes have been 
difficult to recover from sub-fossil material, restricting the scope of 
ancient DNA research. Here, we have isolated single-locus nuclear DNA 
markers to assign the sex of 115 extinct moa and, in combination with a 
mitochondrial DNA phylogeny, tested competing hypotheses about the specific 
status of moa taxa.  Moa were large ratite birds that showed extreme size 
variation both within and among species.  For some taxa, this large 
variation was hypothesized to represent sexual dimorphism, while for others 
it was argued to reflect the existence of different species.  Our results 
show that moa were characterized by extreme reverse sexual dimorphism and as 
a result we have been able to clarify the number of moa species. For 
example, we show that the three recognized 'species' of _Dinornis_ comprised 
only two monophyletic groups and that two of these 'species' comprised 
individuals of one sex only.  This study also illustrates that single-locus 
nuclear DNA sequences can be consistently recovered from ancient material."


The study determined that only two _Dinornis_ species existed in the 
Holocene of New Zealand - one on the North Island, one on the South Island.  
Also, females are estimated to have been almost twice as massive and males, 
based on femoral length.  The study also confirms a previous interpretation 
that the smaller dinornithid species _Euryapteryx curtus_/_E. exilis_, 
_Emeus huttonii_/_E. crassus_, and _P. septentrionalis_/_P. mappini_ 
generally represent males and females of the same species in each case.



Tim

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