Turvey Samuel T, Green Owen R, Holdaway Richard N
School of Biological Sciences, University of Canterbury, Private Bag 4800, Christchurch 8020, New Zealand.
Nature. 2005 Jun 16;435(7044):940-3. doi: 10.1038/nature03635.
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 tetrapods. However, the growth periods of ornithurines (the theropod group including all modern birds) are usually apomorphically shortened to less than a year, so annual growth marks are almost unknown in this group. 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.
成年体型达到之前在皮质骨中沉积的周期性生长标记，反映了由年度节律引起的成骨变化，是非鸟类变温动物和恒温四足动物中的普遍现象。然而，今鸟型类（包括所有现代鸟类的兽脚亚目类群）的生长周期通常特化为短于一年，因此该类群中几乎不存在年度生长标记。在此我们表明，皮质生长标记在新西兰恐鸟（鸟纲：恐鸟目）的长骨中很常见，恐鸟目是最近灭绝的平胸总目目。恐鸟表现出过去在新西兰鸟类区系中常见的夸张的K选择生活史策略，在某些情况下需要近十年才能达到骨骼成熟。这表明相对于所有现存鸟类，恐鸟的生殖成熟极度延迟。目前认可的两个恐鸟科（恐鸟科和艾氏恐鸟科）也表现出不同的出生后生长速率，这与它们体型的相对差异有关。与体型较小的艾氏恐鸟科物种相比，两种巨型恐鸟属恐鸟通过加快幼体生长速率而非延长骨骼生长周期来达到其巨大的体型（活体质量可达240千克）。
