An Ancient Hitch-Hiker

The fantastic computer model of the 50 million year old,
amber preserved spider with a mite hitch-hiking on its back

In recent times, samples of amber have revealed many fantastic specimens. They have given us  fantastic new knowledge about the evolution of everything from arthropod groups to feathers. Sometimes the fossils which they give up are not exciting new species or revolutionary insights into evolutionary history, but are instead curious specimens which are simple snapshot of a single moment in time, perfectly preserved for millions of years.

Such a piece was recently unearthed at the world famous, 50 million year old Baltic Sea deposits. A team from the University of Manchester analysed the amber fossil, using the most advanced computer scans and modelling available. In recent years, advances in computing power and innovative new analysis techniques have allowed palaeontologists to study fossils and extract a greater wealth of detail than ever before. A couple of decades ago, fossils required a physical study utilising arduous and inaccurate processes which risked damaging the specimens.

Now CT scans, MRI imaging and synchotron x-ray analysis can collect vast amounts of data to create 3D digital models, which are accurate to scales of hundredths of micrometres, with no damage to the specimens themselves. Inside this particular piece of amber, they found a spider, barely 156 micrometres in length, just visible to the naked eye. What made it special was that there was an even smaller mite, a type of arachnid, hitching a lift upon its back.

The specimen was described as 'one in a hundred thousand.' The hitch-hiking, better known as phoretic behaviour, is used by small creatures as a means of getting a free ride to a new and potentially food-rich environment. Fossil mites themselves are incredibly rare, making the discovery of this specimen a fantastic find. The scientists also believe that it is the oldest known member of the modern day mite family, Histiostomatidae.

They were able to draw this conclusion by using the computer to dissect the models, removing the mite from the spider's back, allowing them to view its underbelly. Professor Phil Withers, co-author of the paper published in the Royal Society journal Biology Letters, from Manchester's School of Materials, said: 'We believe this to be the smallest amber inclusion scanned anywhere to date. With our sub-micron phase contrast system we can obtain fantastic 3D images and compete with synchrotron x-ray systems and are revealing fossils previously inaccessible to imaging. With our nano-CT-lab systems, we are now looking to push the boundaries of this technique yet further.'