Ancient DNA studies showed the female moa (Dinornis) was much larger than its male counterpart. A pigeon skeleton (bottom right) is included for scale.
The extinct Haast's eagle attacking a moa. Image: John Megahan
80 million years ago the landmass that constitutes New Zealand separated from the southern “super-continent” called Gondwana. Following the extinction of dinosaurs 65 million years ago New Zealand did not “follow” the evolutionary path of other landmasses, in that birds rather than mammals became the dominant herbivore. Prior to human settlement 700 years ago New Zealand had no terrestrial mammals - apart from three species of bats - instead approximately 250 avian species dominated the ecosystem half of which are now extinct.
The lack of mammals is thought to of prompted the evolution of many flightless birds, the most striking of which is the herbivorous moa (pictured) - approximately 10 species of which lived in different habitats in New Zealand's North and South Island (pictured). Moa were ill-adapted to deal with the introduction of humans and rodents, and were driven to extinction about 500-800 years ago.
Human males have an X and a Y chromosome, whereas females are XX, therefore the DNA on the Y chromosome can positively identify DNA as being male. Researchers have employed a similar approach with ancient moa DNA to identify the sex of moa bones (Bunce et al. 2003 and Huynen et al. 2003) - this research was some of the first use of ancient nuclear DNA to determine characteristics of extinct fauna. The data conclusively demonstrated that females were substantially larger than males (up to 3 times the mass), a phenomenon known as reversed sexual dimorphism. The image on this page compares an averaged sized male and female with a pigeon as a scale. Research using ancient DNA and isotopes to understand the taxonomy, evolutionary history and diet is ongoing. In 2006 we secured a 3 year Marsden grant (for $825,000) to AMS 14C date and profile (with stable isotopes and DNA) moa from two North Canterbury swamps. The goal of the research is to increase our understanding of moa ecology and the environment which they occupied.
Among other extinction events in New Zealand was the Haast's eagle (Harpagornis moorei). Haast’s eagle (10-15kg, 2-3 m wingspan) (Holdaway 1994) was 30-40% heavier than the largest extant eagle (the Harpy eagle,) and hunted moa up to 15 times its weight (pictured). In a dramatic example of morphological plasticity and rapid size increase, we show that the Haast’s Eagle was not related to the Australian wedge-tailed eagle but very closely related the world’s smallest extant eagles (the Australian Little Eagle), approximately 1/10th its mass. This spectacular evolutionary change illustrates the potential speed of size alteration within lineages of vertebrates, especially in island ecosystems.