Palaeoclimate across an altitudinal gradient in the Oligocene - Miocene of northern Tasmania: an investigation of nearest living relative analysis

An examination of the nearest living relatives (NLRs) of macrofossil taxa that occur in at least two of five Oligocene-Miocene fossil sites in northern Tasmania indicates that those with mesothermal affinities are restricted to the low altitude sites. Since this occurs over a wide range of taxa, it is clear support for the hypothesis that an altitudinal temperature gradient occurred during the Oligocene-Miocene in Tasmania. Among the high diversity of Dacrycarpus macrofossils present in the deposits, there is morphological evidence that the species found at the highest altitude site (Monpeelyata) grew in a climate that is outside the range encompassed by extant species, suggesting that there has been selective extinction within this genus, resulting in a narrowing of the climatic range in which it occurs today. Two subgenera of Nothofagus Blume (Lophozonia (Turcz.) Krasser and Nothofagus) show a trend in leaf size among Cenozoic localities in Tasmania, but the rate of change apparently varies between the two. In both cases the trend is towards smaller leaves in higher altitude and/or more recent (i.e. cooler) deposits. Nearest living relative analysis is shown to be an extremely valuable technique in palaeoclimate reconstruction if it is applied in sufficient detail, although at present it is best applied qualitatively.