News in Science

Lost relative of Gondwanan relic found

Gondwana plants Fossil remains of an ancient relative of one of Australia's 'living fossils' have been found in New Zealand, supporting the idea that the lineage was once widespread across the southern hemisphere.

Palaeobotanist Dr Ray Carpenter, of University of Adelaide, and colleagues, report their findings in a recent issue of the American Journal of Botany.

"It's quite exciting to us that we've got some material that's 20 million year old and it's in New Zealand," says Carpenter.

The shrubby conifer Microcachrys tetragona only grows in the alpine areas of Tasmania.

"They're often found creeping across and among boulders," says Carpenter.

The shrub is believed to be a 'living fossil' - part of an ancient lineage dating back to the time of the dinosaurs.

"It's the last representative of a group that had a common ancestor," says Carpenter.

Microcachrys is a member of the Podocarpacae family, which is in the same group as the Huon pine. Another well known living Gondwana fossil, the Wollemi pine, is a member of the Araucariaceae family, to which Norfolk pines belong.

Pollen evidence

Pollen evidence suggests microcachrys-type plants were once widely distributed across the southern hemisphere.

Microcachrys-type pollen grains are tiny and spherical, with three wings on them to aid in wind dispersal.

Such pollen grains have been found dating back 150 million years in sediments from Tasmania and Patagonia to southern Africa and Antarctica.

But, says Carpenter, to date no microcachrys-type leaves or cones have been found in the fossil record.

It should be possible to recognise them because of the unique square arrangement of its leaf, he says.

"If you were to take a cross section through a leafy shoot of microcachrys you would see the leaves are arranged in a square manner," says Carpenter.

Now, with the help of colleagues in New Zealand and Tasmania, Carpenter has found evidence of microcachrys leaves in a layer of leafy material embedded in coal taken from a mine in southern New Zealand.

The fossil leaves not only had the square ranking, but microscopic studies of the waxy leaf cuticle found it had characteristic features of microcachrys.

"So we were confident that it's microcachrys," says Carpenter.

Dated as 20 million years old, these are the oldest fossil of microcachrys leaves to be found, and the first to be found outside Australia.

The fossil plant is a new species and has been called M. novae-zelandiae.

The findings confirm microcachrys plants sometimes lived in swampy habitats - the conditions required for preservation of plant fossils.

They also confirm suggestions from the pollen record that in the past microcachrys had a much wider distribution across the southern hemisphere.

And they emphasise the importance of Tasmania as a refuge for such plants. The island is home to a number of Gondwanan relics, including other conifers and flowering plants.

Carpenter explains why Tasmania's could be a good place to preserve Gondwanan lineages.

"There's lots of landscape and microclimatic variation within a small base in Tasmania so it gave plants the opportunity to change their distribution to adapt to climate change," he says.