Every biologist has a gateway species. The taxon you had never heard of before that just looked so weird and unusual that you had to learn more. So, you looked up a few books, searched some library holdings, maybe photocopied a few journal articles (if you’re an old). From that small hook, a wider, more wonderful world opened up. You caught a glimpse of the tangled bank; the tapestry of life with its many threads that cross like warp and weft through space and time.
For me this was the moa. I remember it very clearly. I had read of recent attempts to generate ancient DNA from the extinct giant ratites of New Zealand and was instantly intrigued. I was in my third year of an undergraduate degree in biology and considered myself fairly au fait with the global biota. But these creatures were like nothing I’d encountered before. In reconstruction they were like fluffy pom-poms, with ten-foot necks, dragon legs, and tiny heads. An ostrich drawn by a two year old. The skeletons were just as impressive. Ribcages on legs with endless vertebrae. I think what blew my mind was that this whole family of birds (Dinornithiformes) had survived in their overlooked Eden until the time of William Wallace (very recent indeed, for a Scotsman), but had gone extinct due to overhunting and introduced predators. This was my first inkling of a fact that has become a lifelong theme: extinction is not a thing of the remote past of dinosaurs and mammoths, but is happening right now! Now! This very minute! It was a watershed moment for someone who until then had blindly believed in the ability of ecosystems to be self-regulating and stable, excepting meteors and ice ages. It was more like a coming of age. A realisation that if humans are going to claim dominion, then we have a fundamental responsibility towards our fellow species.
The moa (singular and plural, taken from Mãori) were an incredible family of birds. Part of the ratite group, familiar to us in the modern day ostrich (Struthio camelus), emu (Dromaius novaehollandiae), kiwi (Apteryx sp.), cassowaries (Casuarius sp.), and rhea (Rhea sp.), they are also kin to the extinct elephant birds (Aepyornithidae). When I first read about the moa, they had just been taxonomically culled from a couple dozen species down to a more manageable twelve or so. There were a complex bunch of genera and species: some turkey sized, others larger. The most impressive of the group were the Dinornis sp. which could be nearly two metres tall at the back, with a potential reach of up to four metres, thanks to their hosepipe necks. All fitted into the wide variety of New Zealand ecosystems: rainforest, alpine, coastal, plains. Since New Zealand, famously, has no native mammals, the moa had evolved into a broad spectrum of niches. Some were browsers, some grazers, some specialised, some catholic in their food choices. There is evidence that some of the native flora co-evolved with moa a unique form of browsing defence (“divaricating”) where the tender growing heart is protected by a mass of wide-angled branches and thorns. Like the Osage orange and Honey locust in the New World, the ghosts of evolution with megafauna are still around.
Since the New Zealand extinction event is so recent, the evidence it has left behind is much greater than that found in Australia, America, or Europe. Moa bones, eggshell and other detritus are everywhere. My PhD supervisor (a caver, and native Kiwi) told an amusing story about using a moa tibiotarsus to loop his rope around when exploring underground. The first moa bones to be identified had a very prominent place in 19th century geology: they were shipped over by Walter Mantell (son of the revered Gideon Mantell, finder of the first dinosaurs) and identified from the merest scrap by the nefarious Richard Owen. This set off a mad scramble for everything moa, with huge numbers of bones being uncovered by interested amateurs.
As the extinction was relatively recent, there are many remains of moa that speak more forcefully than bones ever could. There are mummies of some species of moa. Preserved in dry alpine caves, we can look at the face of an extinct giant and imagine what it would have been like when alive. We can admire the beautiful feathers. Soft and downy in muted browns and greens. Used in ceremonial robes and cloaks by Mãori leaders. Coprolites of moa have been found and studied and give an insight into diet and ecology. The enormous eggs (only slightly smaller than those of the Malagasy Elephant bird) have been recovered in archaeological contexts and abandoned nests. Even preserved footprints have been found, showing how the birds strode over the land they once owned. The Mãori even depicted them in art. As a complex and multifaceted society, the Polynesians who travelled to New Zealand and became the Mãori must have incorporated the many species of moa into their culture. At least until they became extinct. 19th century European ethnologists who quizzed Mãori elders about moa may have hopelessly contaminated their source with leading questions and nonsensical pet theories, but some scraps of genuine knowledge appear to have come through. Most poignant to me is a proverbial Mãori expression of loss and regret: “Ka ngaro i te ngaro o te moa”. This translates as “Lost, as the moa is lost”.
Moa have really come into their own as a subject of study with the advent of ancient DNA methods. Being large, extinct, unique, and not very old they were the perfect source of DNA. In fact the first genome from any extinct species was from a pair of moa (the study that started me out on my current trajectory…). Despite a century’s worth of work on skeletal morphology and how it related to moa taxonomy, the greatest revelation about living moa came from a fantastically elegant study conducted by my friend and mentor Professor Mike Bunce, all the way back in 2003. Here, genetic study of three putative species of moa uncovered conclusive evidence that the three different sizes of moa were actually two sexually dimorphic species. Basically, there were super-large, large, and medium animals on the North and South island of New Zealand. On the North Island, the large bones were identified as females and the medium bones as male. On the South Island, the super-large bones were the females and the medium bones were males. By sequencing DNA from the sex chromosomes Mike and colleagues were able to identify female moa (in contrast to mammals, bird sex chromosomes are heterogametic in the females, usually identified as ZW). Like ostriches, for moa the smaller males were probably in charge of egg care.
And so to their extinction. As an enormous, flightless bird with no natural predators (except perhaps the enormous Haast’s eagle, Harpagornis moorei), moa probably invested a lot of their effort into a few offspring, which took a long time to reach maturity. Juvenile moa may not have attained maturity until they were at least a decade old, according to growth rings recorded in their bones. This strategy, known as K-selection, is often found in large animals as the best method for reproductive success. Unfortunately, it also means that very little interference was needed to irrevocably condemn the moa to extinction. Numerous modelling studies have shown that from the arrival of the Polynesians in the first fleet to total extinction of the moa could have taken as little as 150 years. Up to 100,000 moa from 11 different species wiped out by hunting, land clearance, dogs and rats in a century and a half:
Ka ngaro i te ngaro o te moa.
Written by Ross Barnett (@DeepFriedDNA)
Allentoft, M. E., & N. J. Rawlence. (2012). “Moa’s Ark or Volant Ghosts of Gondwana? Insights from Nineteen Years of Ancient DNA Research on the Extinct Moa (Aves: Dinornithiformes) of New Zealand.” Ann Anat 194, no. 1: pp.36-51. [Abstract only]
Bunce, M., T. H. Worthy, T. Ford, W. Hoppitt, E. Willerslev, A. Drummond, and A. Cooper. (2003). “Extreme Reversed Sexual Size Dimorphism in the Extinct New Zealand Moa Dinornis.” Nature 425, no. 6954: pp.172-75. [Full article]
Bunce, M., T. H. Worthy, M. J. Phillips, R. N. Holdaway, E. Willerslev, J. Haile, B. Shapiro, et al. (2009). “The Evolutionary History of the Extinct Ratite Moa and New Zealand Neogene Paleogeography.” [In eng]. Proc Natl Acad Sci U S A 106, no. 49: pp.20646-51. [Full article]
Cooper, A., C. Lalueza-Fox, S. Anderson, A. Rambaut, J. Austin, and R. Ward. (2001). “Complete Mitochondrial Genome Sequences of Two Extinct Moas Clarify Ratitie Evolution.” Nature 409. pp.704-07. [Full paper]
Holdaway, R. N., M. E. Allentoft, C. Jacomb, C. L. Oskam, N. R. Beavan, and M. Bunce. (2014). “An Extremely Low-Density Human Population Exterminated New Zealand Moa.” Nat Commun 5. pp5436. [Abstract only]
Mitchell, K. J., B. Llamas, J. Soubrier, N. J. Rawlence, T. H. Worthy, J. Wood, M. S. Lee, and A. Cooper.(2014). “Ancient DNA Reveals Elephant Birds and Kiwi Are Sister Taxa and Clarifies Ratite Bird Evolution.” Science 344, no. 6186: pp.898-900. [Full article]
Oskam, C. L., J. Haile, E. McLay, P. Rigby, M. E. Allentoft, M. E. Olsen, C. Bengtsson, et al. (2010). “Fossil Avian Eggshell Preserves Ancient DNA.” Proceedings Of The Royal Society B-Biological Sciences 277, no. 1690: pp.1991-2000. [Full article]
Perry, G. L. W., A. B. Wheeler, J. R. Wood, and J. M. Wilmshurst. (2014). “A High-Precision Chronology for the Rapid Extinction of the New Zealand Moa (Aves, Dinornithiformes).” Quaternary Science Reviews 105: pp.126-35. [Abstract only]
Rawlence, N. J., J. R. Wood, K. N. Armstrong, and A. Cooper. (2009). “DNA Content and Distribution in Ancient Feathers and Potential to Reconstruct the Plumage of Extinct Avian Taxa.” Proceedings of the Royal Society of London: Series B. [Full article]
Rawlence, N. J., J. R. Wood, R. P. Scofield, C. Fraser, and A. J. D. Tennyson. “Soft-Tissue Specimens from Pre-European Extinct Birds of New Zealand.” Journal of the Royal Society of New Zealand (2012): 1-28.[Full Article]
Turvey, S. T., O. R. Green, and R. N. Holdaway. (2005). “Cortical Growth Marks Reveal Extended Juvenile Development in New Zealand Moa.” Nature 435, no. 7044: pp.940-3. [Abstract only]
Wood, J. R. (2008). “Moa (Aves: Dinornithiformes) Nesting Material from Rockshelters in the Semi-Arid Interior of South Island, New Zealand.” [In English]. Journal of the Royal Society of New Zealand 38, no. 3: pp.115-29. [Full article]
Wood, J. R., N. J. Rawlence, G. M. Rogers, J. J. Austin, T. H. Worthy, and A. Cooper. (2008). “Coprolite Deposits Reveal the Diet and Ecology of the Extinct New Zealand Megaherbivore Moa (Aves, Dinornithiformes).” Quaternary Science Reviews. [Abstract only]