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Extreme reversed sexual size dimorphism in the extinct New Zealand moa Dinornis


The ratite moa (Aves; Dinornithiformes) were massive graviportal browsers weighing up to 250 kg (ref. 1) that dominated the New Zealand biota until their extinction approximately 500 yr ago. Despite an extensive Quaternary fossil record, moa taxonomy remains problematic1,2,3,4 and currently 11 species are recognized. Three Dinornis species were found throughout New Zealand and differed markedly in size (1–2 m height at back) and mass (from 34 to 242 kg)1. Surprisingly, ancient mitochondrial DNA sequences show that the three species were genetically indistinguishable within each island, but formed separate North and South Island clades. Here we show, using the first sex-linked nuclear sequences from an extinct species, that on each island the three morphological forms actually represent just one species, whose size varied markedly according to sex and habitat. The largest females in this example of extreme reversed sexual size dimorphism were about 280% the weight and 150% the height of the largest males, which is unprecedented among birds and terrestrial mammals. The combination of molecular and palaeontological data highlights the difficulties of analysing extinct groups, even those with detailed fossil records.

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Figure 1: Size and distribution of the three currently accepted Dinornis species.
Figure 2: The maximum a posteriori tree of Dinornis mitochondrial DNA sequences generated from the posterior distribution using Metropolis–Hastings MCMC and control region sequences (525 bp) of 32 specimens, with protein-coding sequences (1,435 bp) from 7 specimens (see Methods).
Figure 3: Molecular sex determination of Dinornis.
Figure 4: Occurrence of Dinornis skeletal remains from swamp and cave deposits across New Zealand.


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We thank the Museum of New Zealand Te Papa Tongarewa (A. J. D. Tennyson, J. A. Bartle), Canterbury Museum (P. Scofield), Auckland Museum (B. Gill), Otago Museum (S. Michelsen-Heath), B. Reeve, Bell Hill Vineyard (M. Giesen, S. Veldhuizen), Pampas Poultry (H. Macfie), B. Shapiro, T. Gilbert, R. Holdaway, J. Binladen and T. Brand for samples and assistance with analysis. The Oxford University Museum of Natural History provided laboratory space. We thank NERC (A.C. and M.B.), Wellcome and Leverhulme Trusts (A.C.), BBSRC (T.F., W.H., A.D., A.C.), EPSRC (A.D.), Villum Kann Rasmussen Fonden, Denmark (E.W.) and the New Zealand FoRST (T.H.W.) for financial support.

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Correspondence to Alan Cooper.

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Bunce, M., Worthy, T., Ford, T. et al. Extreme reversed sexual size dimorphism in the extinct New Zealand moa Dinornis. Nature 425, 172–175 (2003).

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