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Sexual dimorphism in moas

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.


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