Wednesday, March 1, 2017

March of the Moa Part 1: Evolution and History on New Zealand

The moa (Dinornithiformes) are a group of flightless birds which lived on New Zealand from the middle Miocene and survived until the late 14th to early 15th century: around the time Europe was transitioning out of the Middle Ages and into the Renaissance period. They were the largest and most influential vertebrates within New Zealand’s terrestrial ecosystems and there were 9 species within 6 genera and 3 families by the arrival of the first human settlers 700 years ago. More information is known about moa than arguably any other completely extinct animal group with everything from complete skeletons and eggshells to preserved soft tissues containing ancient DNA being collected. This post will, therefore, serve as the first entry in a 5-part series summarizing our current understanding of these great birds.

Skeleton of the South Island Giant Moa (Dinornis robustus)
on display at the Yorkshire Museum, England. Wiki.

Prior to 2010, it was believed that moa were most closely related to Australian emus and cassowaries among modern birds. It has since been realized, however, that the closest living relatives to moa are the tinamous (Tinamidae): a family of small South American ground birds which resemble gamefowl. It is a mystery how these South American birds, which are relatively poor flyers, managed to cross the 12,304km (7,645.2 miles) of open ocean to reach the islands of New Zealand. Perhaps they arrived by island-hopping or by rafting over the course of millions of years. Another possibility is that tinamous, or a close relative, already existed on New Zealand by the early Oligocene when there was less distance between New Zealand and Antarctica with only a shallow sea separating them, while Antarctica itself was still connected to South America. This latter hypothesis is supported by the presence of meiolaniid and pleurodire turtles, mekosuchine crocodiles, and mystacinid bats living in New Zealand during the early Miocene, all of which share South American or Australian origins and are unlikely to have arrived by crossing deep ocean. Once established in New Zealand, however, ancestral moa underwent a remarkable adaptive radiation taking on the role of mid-sized to large terrestrial herbivores in the absence of mammalian competitors. 

An Elegant-crested Tinamou (Eudromia elegans), one of many species
of volant, ground-dwelling birds from Central and South America. Tinamou
are the closest living relatives of the moa. Wiki.

The exact timing of when the moa ancestor first arrived in New Zealand is up for debate, but the earliest definitive moa fossils are known from the early to late Miocene Saint Bathans Fauna. By this period, moa were already large-sized, flightless, and had similar skeletal anatomy to that of their more recent relatives, implying that their origin and arrival to New Zealand was much earlier than this. The radiation of the 9 Holocene species occurred primarily in South Island and was influenced by the accelerated uplifting of the Southern Alps during the late Miocene (6mya), an event which altered New Zealand’s climate and created new biomes which encouraged the evolution of new species to exploit themSouth Island, the larger of the two main islands of New Zealand, has three main habitat zones:
  1. The colder highlands of the Southern Alps run from the north to the south of the island, influencing the rainfall and vegetation on either side.
  2. The land to the west of the Southern Alps is densely-forested with high rainfall,
  3. To the east of the mountains lay drier woodlands, shrublands, and grasslands which comprise much of the lowland area.
North Island experiences high rainfall and is dominated by deciduous forest habitat much like the western lowland area of South Island, while the land closer to the southern coast is drier and more open. The more diverse range of habitats of South Island combined with its larger land area (150,437km² to North Island's 113,729km²) explains why moa diversity is highest on South Island: 7 of the 9 species lived (5 of which being endemics) lived on South Island while just 4 species (with 2 endemics) inhabited North Island.

New Zealand split from the supercontinent of Gondwana during the late Cretaceous
and is currently situated about 1,500km east of Australia and 5,000km north of Antarctica.
 Because of its remoteness, it was the last habitable landmass to be colonized by humans.
Most of its endemic animals descended from taxa that colonized it during the
late Mesozoic or early Cenozoic when it was still relatively close to larger landmasses. 
In later Cenozoic times, volant birds from Australia periodically flew here and 
radiated into new endemics.

Genetic evidence suggests that the 9 Holocene species of moa radiated from a common ancestor during the late Miocene with the Upland Moa (Megalapteryx didinus), the sole member of the family Megalapterygidae, being the most basal. The two species of Dinornis within the family Dinornithidae were the largest and tallest of the moa very slender skeletons and elongated limbs adapted for mobility. The family Emeidae is the most diverse, containing the remaining 6 species within 4 genera: 3 species within Pachyornis and the genera Anomalopteryx, Euryapteryx, and Emeus containing a single species each. Contained within this family are the smallest, as well as some of the most heavily-built moa.

Reconstructed skulls of the 9 species of moa shown to scale, alongside
silhouettes of each species. Restored skulls are drawn from specimens from 

the online collections of Museum of  New Zealand Te Papa Tongarewa. 
Scale bar in lower left corner equals 3cm.

Part 3: Paleoecology
Part 4: Behavior
Part 5: Extinction

References & Further Reading
Huynen L, Suzuki T, Ogura T, Watanabe Y, Millar CD, Hofreiter M, Smith C, Mirmoeini S, Lambert DM (2014). "Reconstruction and in vivo analysis of the extinct tbx5 gene from ancient wingless moa (Aves: Dinornithiformes)". BioMed Central Evolutionary Biology 14:75 <Full Article>

Allentofta ME, Hellerd R, Oskamb CL, Lorenzena ED, Halec ML, Gilberta TP, Jacombg C, Holdawayc RN, Bunce M (2014). "Extinct New Zealand megafauna were not in decline before human colonization". PNAS 111(13): 4922–4927 <Full Article>

Brassey CA, Holdaway RN, Packham AG, Anne´ J, Manning PL, Sellers WI (2013). "More than one way of being a moa: differences in leg bone robustness map divergent evolutionary trajectories in Dinornithidae and Emeidae (Dinornithiformes)". PLoS ONE 8(12): e82668. doi:10.1371/journal.pone.0082668 <Full Article>

Hand SJ, Worthy TH, Archer M, Worthy JP; Tennyson AJD, Scofield RP (2013). "Miocene mystacinids (Chiroptera, Noctilionoidea) indicate a long history for endemic bats in New Zealand". Journal of Vertebrate Paleontology 33(6): 1442-1448 <Full Article>

Rawlence NJ, Metcalf JL, Wood JR, Worthy TH, Austin JJ, Cooper A (2012). "The effect of climate and environmental change on the megafaunal moa of New Zealand in the absence of humans". Quaternary Science Reviews 50: 141-153 <Full Article>

Morten A, Rawlence N (2012). “Moa’s ark or Volant ghosts of Gondwana? Insights of nineteen years of ancient DNA research on extinct moa (Aves: Dinornithiformes) of New Zealand”. Animals of Anatomy 194: 36-51 <Full Article>

Worthy TH (2011). "Terrestrial turtle fossils from New Zealand refloat Moa's Ark". Copeia 1: 72-76 <Full Article>

Tennyson AJD, Worthy TH, Jones CM, Scofield RP, Hand SJ (2010). "Moa’s Ark: Miocene fossils reveal the great antiquity of moa (Aves: Dinornithiformes) in Zealandia". Records of the Australian Museum 62: 105–114 <Full Article>

Buncea M, Worthy TH, Phillips MJ, Holdaway RN, Willerslev E, Hailef J, Shapiro B, Scofieldi RP. Drummond A, Kamp PJJ, Cooper A (2009). "The evolutionary history of the extinct ratite moa and New Zealand Neogene paleogeography". Proceedings of the National Academy of Science 106(49): 20646–20651 <Full Article>

TH Worthy (1990). "An analysis of the distribution and relative abundance of moa species (Aves: Dinornithiformes)". New Zealand Journal of Zoology 17(2): 213-241 <Full Article>

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