Subsequent dating of Pacific rat bones sampled from both laughing owl (32) and archaeological sites (33–38).The most telling criticism of the original dates is that they fall into two distinct groups according to when the bones were processed in the same dating laboratory (22, 36, 37) (see Fig. The early series of rat bone dates processed in 19 are all older than the oldest-dated archaeological evidence (≈1280 A.D.), but all bones dated after 1996 are younger (36, 37) (Fig. Moreover, some rat bones from archaeological assemblages that were processed in 19 are significantly older than consistent dates on diverse materials from the same stratigraphic contexts (34, 35).Critics argued that this unusual bimodal distribution of ages according to when the bones were processed was due to inadequate pretreatment of small bones (33, 35 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).Our earlier dates on 32 rat-gnawed seeds from the North Island (22) (Fig.
ages from previous studies (20, 21) also shown in their laboratory processing order (1995–19–1998) (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. The contentious early series of old rat bone dates (20, 21) is the only direct evidence in support of an early human presence in New Zealand. We also dated 13 rat bones selected from the same collections of bones originally excavated and now held in museum collections, representing seven of the 1995–1996 series of rat bone sampling sites (20, 21): Predator Cave, Hawke's Cave, Earthquakes #1, Gordon's Valley (sites 2a, 4, and 7), Hanging Rock, Ardenest, and Timpendean (Fig. The calibrated ages of rat bones from these museum collections are also all younger than 1280 A. and overlap only with our reexcavated rat bone dates and with other rat bone dates processed in 19 (Fig. Locations of laughing owl bone sites, seed deposits, and seed test pits in New Zealand.
Our method exploits the fact that the omnivorous rat was transported throughout the Pacific by prehistoric people and multiplied rapidly after its initial introduction.
Consequently, introduction of rats to previously rat-free islands is unlikely to remain invisible in the palaeoecological record for any length of time.Thus, suggestions of dietary-related offsets (39, 40) are untenable as an explanation for the old rat bone dates processed in 1995–1996.