甲壳虫特点
Beetle fossils are commonly preserved as disarticulated skeletal fragments (fig. 2) in organic sediments such as clays, peats, sands and silts (Porch & Elias,2000).Beetles preserve well due to their robust nature and structural details can often be distinguished allowing them to be identified to species level. In most cases identification has revealed fossilized beetles to be extant species indicating a great degree of morphological constancy throughout the Quaternary. This constancy includes that of key characters, such as genitalia, used in the identification of species.
As morphology does not appear to have evolved it is generally assumed that the physiological requirements of beetles have also remained constant. Evidence to support this assumption exists in the fact that the composition of beetle communities has, like morphology, remained relatively constant throughout the Quaternary and that host-specific phytophagus species can be sometimes be found in association with macrofossils of their host plant. Due to this observed constancy and the ectothermic nature of beetles – and thus their reliance on environmental conditions – beetle fossils can therefore make excellent indicators of pale environment. The first climate and environmental reconstruction using beetle fossils was published by Coope. Since this time beetle fossils have been increasingly used for reconstructing past environments and the associated climate. Initially this work was restricted to the United Kingdom but soon spread to continental Europe and North America. Since then the number of studies utilizing beetle remains to reconstruct the pale environment has continued to increase, primarily in the Northern Hemisphere, but also in South America and recently there has been discussion of the potential for this research in Australia. In 2002 the first New Zealand study using beetle fossils to reconstruct pale climate and pale environment was completed proving that this technique is usable in New Zealand and laying the groundwork for this study. While the use of beetle fossils for pale climatic and pale environmental reconstruction has increased over the last four decades it is still little used when compared to other biological proxies, and in New Zealand palaeo environmental analysis is dominated by palynology even though the flora of New Zealand is temperature-tolerant making quantification of palaeo climate difficult. Other methods of environmental and climatic reconstruction used in New Zealand are tree rings, phytoliths, aerosolic quartz influx, glacial equilibrium-line estimates, speleothems and diatoms. Fossil beetle analysis has a number of advantages over other biological proxies such as pollen. Beetles are the most diverse group of organisms filling a large range of ecological roles and habitats from deserts to rainforests to the littoral zone. Beetles, and insects in general, respond rapidly to environmental change by dispersal, rather than undergoing speciation, and fossils are generally identifiable to species level in contrast to New Zealand palynological studies where some genera contain species with different ecological requirements, but with indistinguishable pollen.
Predatory and scavenging beetles are able to take advantage of recently modified areas (along with pioneer plant species) before the trees and shrubs with similar climatic requirements. Trees and shrubs can therefore lag behind the actual period of climatic change and the resultant spread of beetles. This ability to rapidly respond to climatic change has also revealed short-term climate fluctuations that are not observed in the pollen record. Beetles fossils also avoid the problem of contamination of the local pollen rain (and hence local climate signal) by long-distance wind dispersed pollen Until the development of the Mutual Climatic Range (MCR) by Atkinson et. al. (1987) studies using beetle fossils were, like palynology, predominantly qualitative in nature. MCR is a method of quantifying paleoclimateand has further increased the usefulness of beetle fossils in reconstructing the past climate of the Quaternary. This quantitative method has enabled studies of beetle fossils to be compared to, or combined with, other proxydata to provide a more complete paleo climatic and paleo environmental reconstruction.
MCR uses the modern distribution of a species found within a fossil beetle assemblage to construct a climate envelope for that species. This is based on the observation that the contemporary distribution of a beetle species is seen to measure its climatic tolerances. Only predators and scavengers are used to calculate MCR as the distribution of some herbivorous species may be limited by the range of a host plant rather than by direct climatic influences. The climate envelopes of all applicable species in the assemblage are overlapped to find the mutual intersection of the climatic ranges. This provides a quantitative measure of the paleoclimate at the time of the assemblage deposition. While providing a quantitative measure of temperature MCR has been found to underestimate maximum temperatures (TMAX) and overestimate minimum temperatures (TMIN) in extremely cold environments. TMIN can also be underestimated in areas with milder winters. However these errors can be corrected for using regression equations. Currently these equations have been calibrated for Europe and North American sites. The recent work by Marra(2002) has also formulated a method of establishing quantitative measures of paleoclimate for the smaller datasets normally extracted from New Zealandsites. Herbivorous beetle species, while excluded from MCR analysis due to their potential relationship to host-plants, are extremely useful in paleoenvironmental reconstruction. Some phytophagus beetle species, such as some scolytids (bark beetles), are restricted in their distribution to certain species of trees. When discovered in a fossil assemblage these beetle species therefore indicate that the required host-plant was present at the study site at the time of deposition. The application of phytophagus beetle fossils for this purpose is possible in a New Zealand context as previously shown by Marra.
老鼠化石研究
An international team of researchers, led by Dr Janet Wilmshurst from Landcare Research, spent 4 years on the project which shows conclusively that the earliest evidence for human colonialization is about 1280-1300 AD, and no earlier. They based their results on new radiocarbon dating of Pacific rat bones and rat-gnawed seeds. Their results do not support previous radiocarbon dating of Pacific rat bones which implied a much earlier human contact about 200 BC.
The original old rat bones dates have been hotly debated ever since they were published in Nature in 1996. The ages are controversial because there is no supporting ecological or archaeological evidence for the presence of kiore or humans until 1280-1300 AD and the reliability of the bone dating has been questioned. This is the first time that the actual sites involved in the original study have been re-excavated and analyzed.
Dr Wilmshurst and her team researchers re-excavated and re-dated bones from nearly all of the previously investigated sites. All of their new radiocarbon dates on kiore bones are no older than 1280 AD. This is consistent with other evidence from the oldest dated archaeological sites, Maori whakapapa, widespread forest clearance by fire and a decline in the population of marine and land-based fauna. “As the Pacific rat or kiore cannot swim very far, it can only have arrived in New Zealand with people on board their canoes, either as cargo or stowaways. Therefore, the earliest evidence of the Pacific rat in New Zealand must indicate the arrival of people” Dr Wilmshurst said.
The dating of the rat bones was also supported by the dating of over a hundred woody seeds, many of which had distinctive tell-tale rat bite marks, preserved in peat and swamp sites from the North and South Islands. “These rat-gnawed seeds provide strong additional evidence for the arrival of rats, and therefore humans, and are an indirect way of testing the veracity of the dates we have done on rat bones,” said Dr Tom Higham, Deputy Director of the Oxford Radiocarbon Accelerator Unit at Oxford University.
Rats leave rows of narrow grooves or bite marks on woody seed cases when they gnaw open the seed, and these distinctive teeth marks can be seen with the naked eye. “The width of the teeth marks left on the woody seeds exactly match those of a rat's two front teeth, and cannot be mistaken for any other seed predator. We have dated over 100 individual seeds, some rat-gnawed, others intact or bird-cracked, which show that rat gnawed seeds only occur in both the North and South Islands of New Zealand after about 1280 AD”, Dr Wilmshurst said.
With over 165 dates on seeds and bones from a large number of sites, the overwhelming evidence suggests that rats and their human carriers did not reach New Zealand until about 1280 AD.
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发表于 2012-12-23 12:57:25
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