Tuesday, 23 October 2012

Ancient Hitchhikers Preserved In Amber

Mayflies are some of the most bizarre insects on Earth. They hatch from eggs which develop quickly into adults with wings. They flutter around for just 24 hours. They feed. They mate. And then die.

The 16 million year old mayfly from the Dominican Republic.
The springtail is the white blog at the base of the  wings
All of their characteristics are hard wired in their DNA, pre-loaded for maximum efficiency in life. We know almost everything about them, but occasionally they throw up some surprising things. Their fossil record extends all the way back into the late Cretaceous some 80 million years ago. Yet some fossils have been found in Carboniferous strata almost 250 million years previously.

New behaviours and body structures have been documented, most recently in a 16 million year old piece of amber from the Dominican Republic. In 2011, an arachnid preserved in Baltic amber was found to have five springtails, segmented arthropods closely related to the insects, clinging to the hooked hairs which covered its legs. They had used the spider as a free ride.

This was the only documented example of phoresy - in which one organism uses another for transportation - in springtails. It inspired Dr David Penney, an expert on amber fossils from the University of Manchester, to examine his own specimens. He had in his collection an example of insect phoresy which consisted of a mayfly with what appeared to be a pseudo-scorpion riding on its back. 'I had initially thought the creature on the mayfly may have been a tiny nymphal pseudo-scorpion, as they are known to use other creatures for transport, and this behaviour is not uncommon to see in amber,' said Dr Penney.

'I didn't truly appreciate the significance of my find until I used the CT scanner and was able to identify the animal as a springtail.' This is the first time phoresy has been recorded in adult mayflies and only the second in the case of springtails. 3000 individual x-rays were used to build up perfect, 3D images of the fossil, revealing a series of details which were invaluable in interpreting the remains.

Using its prehensile antennae, it was hooked into a v shaped depression at the base of the wings. Intriguingly, a 50 micrometre gap between the two suggests that the springtail was in the process of leaping off when it was entombed in the tree resin. The perfect conditions of both animals showed that they died instantly. 'The images are really impressive. This pioneering approach to studying fossils has allowed us an insight into the behaviour of one of the world's most prevalent organisms,' Penney continued.

The ability to use scanning techniques which cause no damage to the fossils has revolutionized our understanding of the Earth's prehistory. The organisms in an ecosystem are important, but the way they interacted with each other is of paramount importance. Only by understanding the subtle connections between the creatures which once existed on the planet, can we truly understand where they came from. The fossils preserved in amber are the closest we will get to seeing into the past.