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, 105 (22), 7676-80

Dating the Late Prehistoric Dispersal of Polynesians to New Zealand Using the Commensal Pacific Rat


Dating the Late Prehistoric Dispersal of Polynesians to New Zealand Using the Commensal Pacific Rat

Janet M Wilmshurst et al. Proc Natl Acad Sci U S A.


The pristine island ecosystems of East Polynesia were among the last places on Earth settled by prehistoric people, and their colonization triggered a devastating transformation. Overhunting contributed to widespread faunal extinctions and the decline of marine megafauna, fires destroyed lowland forests, and the introduction of the omnivorous Pacific rat (Rattus exulans) led to a new wave of predation on the biota. East Polynesian islands preserve exceptionally detailed records of the initial prehistoric impacts on highly vulnerable ecosystems, but nearly all such studies are clouded by persistent controversies over the timing of initial human colonization, which has resulted in proposed settlement chronologies varying from approximately 200 B.C. to 1000 A.D. or younger. Such differences underpin radically divergent interpretations of human dispersal from West Polynesia and of ecological and social transformation in East Polynesia and ultimately obfuscate the timing and patterns of this process. Using New Zealand as an example, we provide a reliable approach for accurately dating initial human colonization on Pacific islands by radiocarbon dating the arrival of the Pacific rat. Radiocarbon dates on distinctive rat-gnawed seeds and rat bones show that the Pacific rat was introduced to both main islands of New Zealand approximately 1280 A.D., a millennium later than previously assumed. This matches with the earliest-dated archaeological sites, human-induced faunal extinctions, and deforestation, implying there was no long period of invisibility in either the archaeological or palaeoecological records.

Conflict of interest statement

The authors declare no conflict of interest.


Fig. 1.
Fig. 1.
Calibrated age ranges of rat bone dates from New Zealand. New calibrated age ranges of AMS dates on R. exulans from Earthquakes #1, Predator Cave, and seven other South Island laughing owl sites from which the original 1995–1996 rat bone dates were derived (20, 21). Blue circles, our reexcavations; red circles, museum collections (see Table S1 for stratigraphic and other details). R. exulans ages from previous studies (20, 21) also shown in their laboratory processing order (1995–1996 and 1997–1998) (40): open diamonds, archaeological sites (36); black diamonds, laughing owl sites (21), showing unusual bimodal distribution (36). Symbols, median age; bars, upper and lower limits of 2σ age range. Vertical dashed lines, 1σ age range of oldest archaeological site in New Zealand (1280–1382 A.D.) (25).
Fig. 2.
Fig. 2.
Locations of laughing owl bone sites, seed deposits, and seed test pits in New Zealand. Symbols show location of redated laughing owl bone sites (20, 21) (blue), seed deposits (red) mentioned in text, and test pits (black) examined during the search for seed sites, but which did not contain preserved seeds.
Fig. 3.
Fig. 3.
Calibrated age ranges of seeds, earliest archaeological evidence, and our oldest rat bones from New Zealand. Horizontal bars represent 1σ calibrated age ranges for seeds (from the oldest to the youngest seed dates) at South Island (this study) and North Island sites (22), including sites with rat-gnawed seeds present and sites with only intact or bird-cracked seeds present. Red circle is the pooled mean age of oldest rat-gnawed seeds from three sites (1σ range with median). Vertical dashed lines represent the 1σ calibrated age range of the oldest archaeological evidence from New Zealand (1280–1382 A.D.) (25). Vertical red bar is the 1σ calibrated age range of our oldest rat bone (OxA 14472), and n, number of dates within each range limit (see Table S2 for details). (Inset) Typical rat-gnawed endocarp (Elaeocarpus dentatus) showing distinctive incisor bite marks (length 8 mm).

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