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Cortical growth marks reveal extended juvenile development in New Zealand moa


Cyclical growth marks in cortical bone, deposited before attainment of adult body size, reflect osteogenetic changes caused by annual rhythms and are a general phenomenon in non-avian ectothermic and endothermic tetrapods1. However, the growth periods of ornithurines (the theropod group including all modern birds) are usually apomorphically shortened to less than a year2,3, so annual growth marks are almost unknown in this group4,5,6. Here we show that cortical growth marks are frequent in long bones of New Zealand's moa (Aves: Dinornithiformes), a recently extinct ratite order. Moa showed the exaggerated K-selected life-history strategy formerly common in the New Zealand avifauna, and in some instances took almost a decade to attain skeletal maturity. This indicates that reproductive maturity in moa was extremely delayed relative to all extant birds. The two presently recognized moa families (Dinornithidae and Emeidae) also showed different postnatal growth rates, which were associated with their relative differences in body size. Both species of giant Dinornis moa attained their massive stature (up to 240 kg live mass) by accelerating their juvenile growth rate compared to the smaller emeid moa species, rather than by extending the skeletal growth period.

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Figure 1: Reconstructions of dinornithid and emeid moa species. A 1.8-m tall person is used as a scale.
Figure 2: Transverse undemineralized diaphyseal thin sections through moa long bones.
Figure 3: Ratite phylogeny and histology.

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We are grateful to R. P. Scofield, H. A. Schlumpf, N. Carson, A. J. D. Tennyson, J. A. Bartle, M. Bunce, T. H. Worthy, L. J. Shorey, T. Robinson, R. Spiers, M. Giesen, S. Veldhuizen, A. Chinsamy-Turan, J. Horner, P. Houde and K. Padian. Funding was provided by a Banks Alecto postdoctoral fellowship from the Royal Society of London (S.T.T.) and the New Zealand Foundation for Research, Science and Technology (R.N.H.).

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Correspondence to Samuel T. Turvey.

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Turvey, S., Green, O. & Holdaway, R. Cortical growth marks reveal extended juvenile development in New Zealand moa. Nature 435, 940–943 (2005).

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