13 May 2010, by Sara Coelho

An amateur geologist from Scotland has found a hoard of exquisitely preserved, 350 million year old fossil tree trunks. The findings reveal the wood's delicate inner structure, including the growth rings that suggest an irregular climate.

Fossil wood

A fossilised wood section photographed through a microscope.

The fossils were discovered by Mrs Elsa Henderson, local resident of Montford in the Isle of Bute and keen fossil hunter, who then contacted Dr Howard Falcon-Lang, a palaeontologist from the Royal Holloway, University of London.

'This shows that geology is a discipline where amateurs can still make a huge difference,' says Falcon-Lang, who researches ancient fossil trees.

Falcon-Lang visited Mrs Henderson in Bute to examine her collection of more than 300 fossil wood fragments. Most specimens occurred as beach pebbles up to 20cm in diameter, but some larger trunks were still in their original position attached to the bedrock.

The wood was preserved for 350 million years due to the substitution of its organic matter by carbonate and silica minerals. 'This happened very early on, possibly in just a few months,' explains Falcon-Lang, adding that the speed of the process allowed the exceptional preservation.

Falcon-Lang selected the best silicified fossils and sliced them into thin sections to reveal the wood's inner cell structure under the microscope. The fossils were classified as wood from the extinct Pitus primaeva tree, thanks to the high level of detail preserved.

'These were big, woody trees, up to 40–45 meters tall,' says Falcon-Lang. 'They are a primitive type of tree related to conifers and an ancestor of modern pines and spruces.'

The thin sections also revealed the trees' growth rings, which can give hints about the growth environment. 'The rings show growth interruptions that suggest a degree of climate irregularity,' says Falcon-Lang, who published the findings in the Scottish Journal of Geology with Mrs Henderson as a co-author.

At the time, Scotland was located near the equator, on the south-east coast of the ancient continent of Laurasia. The climate was warm, with tropical monsoons and dry seasons. 'The growth interruptions probably reflect monsoonal seasonality with occasional droughts,' he says.

Mrs Henderson's findings are not the first fossil tree trunks discovered in Scotland, 'but they are one of the best preserved examples of fossil wood yet found,' concludes Falcon-Lang.