A new take on the evolutionary history of the moa was published in PNAS this week. Mike Bunce from Murdoch University in Perth and researchers from Alan Cooper’s lab at University of Adelaide have combined genetic data from over 260 moa bones with anatomical, geological and ecological information, to revise species relationships among moa and suggest a timeframe and origin for their evolution.
Determining how many species of moa there are, and how they are related to each other has been a problem since moa were first described in 1839. Up to 64 different species and 20 genera have been assigned at various times over the last 160 years. Moa taxonomy has been complicated by the extreme size sexual dimorphism of some species, where females were much larger than males. The number of moa species has only been able to be clarified in recent years with the advent of ancient DNA studies, which enable researchers to determine whether subfossil remains of different sizes actually represent different species, or male and female forms of the same species.
The prevailing view of moa taxonomy from the 1980’s through to 2002 had moa divided into 2 families, Emeidae and Dinornithidae, which contain 8 and 3 species respectively. This new study divides moa into 3 families with the most basal moa lineage Megalapteryx (previously part of Emeidae) elevated to sit in its own family. The six genera remain the same, but only nine species are recognised in this new arrangement.
This study also indicates that these moa species are of more recent origin than previously thought. They appear to have begun diverging around 5.8 million years ago, from a single ancestral species living in the South Island. This is about the time the Southern Alps were forming, and Bunce and colleagues suggest that the increase in habitat diversity that followed enabled the evolution of different species of moa. Some of these species began to disperse to the North Island after the formation of periodic landbridges between the North and South Islands from around 1.5 million years ago. Moa species diversity appears to have then been further shaped by shifts in climate during the glacial cycles of the Pleistocene. Bunce and colleagues suggest that this pattern of evolution – recent South Island origin, followed by rapid diversification influenced by tectonic uplift, marine barriers, and glacial cycles – may be common to many of New Zealand’s iconic endemic species.
Bunce, M., Worthy, T., Phillips, M., Holdaway, R., Willerslev, E., Haile, J., Shapiro, B., Scofield, R., Drummond, A., Kamp, P., & Cooper, A. (2009). The evolutionary history of the extinct ratite moa and New Zealand Neogene paleogeography Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.0906660106