Thursday, March 23, 2017

Heavy-footed Moa (Pachyornis elephantopus)

The Heavy-footed Moa (Pachyornis elephantopus) was the largest member of the genus Pachyornis and the third largest species of moa overall. This exceptionally heavily-built species lived in South Island during the Pleistocene and Holocene where it fed on relatively low-quality plant matter.

Heavy-footed Moa skeleton on display at the Exhibit Museum of
Natural History, University of Michigan. Wiki.

The genus name Pachyornis is derived from the Greek words pachys (meaning “thick”) and ornis (meaning “bird”), a reference to members of this genus being particularly heavily-built compared to other moa genera. The species name elephantopus is a combination of the Greek words elephas (meaning “elephant”) and pous (meaning “foot”). Its full scientific name therefore translates as “Elephant-legged Bird” in reference to this species’ robust skeleton with particularly thick limb elements, a trait which is further emphasized by common name “Heavy-footed Moa”.

Habitat & Distribution
Heavy-footed Moa had an extensive late Quaternary fossil record. Their preferred habitat appears to have been lowland to montane grassland, shrubland, herbfields, and forest margin environments in the eastern and southern parts of South Island. The altitudinal limit for this species appears to have been 700m above sea level as no fossils for it have been found above this point. Heavy-footed Moa underwent significant changes in relative abundance and distribution in response to environmental changes during the late Pleistocene and Holocene. Climatic and environmental fluctuations during glacial cycles caused its preferred habitat to expand and contract repeatedly, resulting in two genetically distinct populations in the northern and southern halves of South Island. Like all other moa, it held a relatively constant population size until the arrival of the Maori in the late 13th century.

Physical Attributes
The Heavy-footed Moa is the third largest species of moa behind both species of Dinornis and is the heaviest moa relative to its size. It stood up to 120cm tall at the hips and 180cm tall when fully erect and weighed up to 145kg, with females being larger than the males. The skeleton was robust with relatively thick leg bones and shortened tarsometatarsi (in birds, the foot bone formed by the fusion of the metatersals). This species is known from desiccated soft tissue remains recovered from cave sites which have preserved skin, tendons, and feathers. From these subfossil remains, we know that this species had shaggy, white-tipped feathers which would give the living animal a mottled or speckled appearance and that the skin of its lower legs were covered in non-overlapping scales like those of most birds. The beak was long, sturdy, and downturned and its overall head was shaped somewhat differently from other moa and was adapted to handle particularly tough vegetation.

Ecology & Behavior
Plant remains from within coprolites and among gizzard stones reveal that Heavy-footed Moa were generalized mixed-feeders with a diet consisting of at least 21 species of particularly fibrous grassland, shrubland, and forest margin vegetation. It grazed on various types of herbs and grasses and browsed on the branchlets of trees and shrubs. As with most of the larger moa species, the only predator of adult Heavy-footed Moa was the Haast’s Eagle (Harpagornis moorei) with the smaller Eyle’s Harrier (Circus eylesi) possibly feeding on the smaller juveniles. Evidence from coprolites further shows that this species hosted several types of taxa-specific parasites.

Heavy-footed Moa are thought to have been less abundant than other moa due to its less frequent representation in the fossil record. Females appear to outnumber males at natural fossil assemblages, suggesting that males were even less common in a given population. This relatively low number of males may be due to increased predation by Haast’s Eagles who likely targeted them more regularly due to their smaller size. Heavy-footed Moa eggs were among the largest of any moa and the only known moa embryos are also attributed to this species. The growth rate of this species is not known. It became extinct abruptly due to human overexploitation and habitat alteration.

References & Further Reading
Attard MRG, Wilson LAB, Worthy TH, Scofield P, Johnston P, Parr WCH, Wroe S (2016). "Moa diet fits the bill: virtual reconstruction incorporating mummified remains and prediction of biomechanical performance in avian giants". Proceedings of the Royal Society of London B 283: 20152043 <Full Article>

Wood JR, Wilmshurst JM, Richardson SJ, Rawlence NJ, Wagstaff SJ, Worthy TH, Cooper A (2013). "Resolving lost herbivore community structure using coprolites of four sympatric moa species (Aves: Dinornithiformes)". PNAS 110(42): 16910-16915 <Full Article>

Rawlence NJ, Wood JR, Scofield RP, Fraser C, Tennyson AJD (2013). "Soft-tissue specimens from pre-European extinct birds of New Zealand". Journal of the Royal Society of New Zealand DOI:10.1080/03036758.2012.704878 <Full Article>

Oskam CL, Allentoft ME, Walter R, Scofield RP, Haile J, Holdaway RN, Bunce M, Jacomb C (2012). "Ancient DNA analyses of early archaeological sites in New Zealand reveal extreme exploitation of moa (Aves: Dinornithiformes) at all life stages". Quaternary Science Reviews 52: 41-48 <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>

Allentoft ME, Bunce M, Scofield RP, Hale ML, Holdaway RN (2010). "Highly skewed sex ratios and biased fossil deposition of moa: ancient DNA provides new insight on New Zealand’s extinct megafauna". Quaternary Science Reviews 29: 753–762 <Abstract>

Huynen L, Gill BJ, Millar CD, Lambert DM (2010). "Ancient DNA reveals extreme egg morphology and nesting behavior in New Zealand’s extinct moa". Proceedings of the National Academy of Science 107(37): 16201-16206 <Full Article>

Wood JR, Rawlence NJ, Rogers GM, Austin JJ, Worthy TH, Cooper A (2008). "Coprolite deposits reveal the diet and ecology of the extinct New Zealand megaherbivore moa (Aves, Dinornithiformes)". Quaternary Science Reviews 27: 2593–2602 <Abstract>

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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