'Smallest fossil' scanned by University of Manchester

The CT scan has allowed biologists to "digitally dissect" the mite

An X-ray scan of Baltic amber at the University of Manchester has revealed what scientists have said is the "smallest arthropod fossil ever".

The 50 million-year-old mite, which was found on a fossilised spider, is just 170 millionths of a metre long.

The find, published in the Royal Society's Biology Letters, was made using computed tomography (CT) which builds up a 3-D image from flat images.

Biologist Dr David Penney said the fossil was "extremely rare".

Baltic amber, the fossilised resin of trees from the area around the Baltic Sea, can contain fossilised arthropods - insects, arachnids and crustaceans - within it, which Dr Penney said were "preserved with lifelike fidelity".

'Remarkable specimen'

The size of the mite means it is barely visible without a microscope and Dr Penney said the team at the university's Faculty of Life Sciences would not have been able to identify it without the CT scan.

"CT allowed us to digitally dissect the mite off the spider in order to reveal the important features on the underside required for identification," he said.

"The specimen, which is extremely rare in the fossil record, is potentially the oldest record of the living family Histiostomatidae.

"Most amber fossils consist of individual insects or several insects together, but without unequivocal demonstrable evidence of direct interaction.

"The remarkable specimen we describe in this paper is the kind of find that occurs only once in, say, a hundred thousand specimens."

The detail of the mite cannot be made out using an optical microscope

Fellow biologist Dr Richard Prezoisi said the CT technology had allowed the team to discover how long species such as the mite had been using larger organisms for transportation.

"Such behaviour is common in several different groups today," he said.

"The study of fossils such as the one we described can provide important clues as to how far back in geological time such behaviours evolved.

"The fact that we now have technology that was unavailable just a few years ago means we can now use a multidisciplinary approach to extract the most information possible from such tiny and awkwardly positioned fossils, which previously would have yielded little or no substantial scientific data."