The Pacific rat – an earlier arrival?
The Pacific rat, known to Māori as kiore, is a poor swimmer and could only have arrived in New Zealand with humans. In the mid-1990s a scientist radiocarbon-dated Pacific rat bones excavated from caves in both the North and South islands, and came up with dates as early as 50–150 AD. This meant that humans must also have arrived by this time, some of them with rats on board. The discovery was a scientific bombshell and the possibility of such an early arrival caused hot debate.
In a Hawke’s Bay cave known as the Hukanui rock overhang, a single rat bone, reportedly found beneath the ash layer from the Taupō eruption of 232 AD, returned a radiocarbon date of 134–320. This was consistent with its position below the ash layer. The bone, which was excavated in 1959 by an amateur archaeologist, lay in a matchbox in the Dominion Museum for 40 years before it was dated. How the bone got beneath the 232 Taupō ash layer is still in dispute.
However, a second rat bone from the Taupō ash layer at the Hukanui rock overhang was dated at around 1300, and a pigeon bone from the same layer was dated at 3,000 years old. As bones in undisturbed sediment layers should be about the same age, this raised some difficult questions. The veracity of the ‘matchbox bone’ is still being debated.
Can rat bones be trusted?
Researchers such as Atholl Anderson haved raised questions about the reliability of rat bones for radiocarbon dating, including:
- Could burrowing animals have moved the rat bones beneath sediment layers?
- Bones from some cave sites gave dates that differed by hundreds of years from the known dates of the layers from which they were unearthed. This suggested that there was something wrong with the rat dates.
- Laboratories might not have prepared the rat bones correctly before dating them or the bones were somehow contaminated during the dating procedure.
- The bones might contain old carbon that the rat had intercepted through the food chain.
If people did arrive as early as 50–150, and introduced the rat, they either died out or did not stay, as there are no other traces of human settlement until 1250–1300.