The soft tissues of ancient animals rarely survive in fossils but how do you preserve them when they do?
That was the puzzle faced by Oxford's Derek Siveter and colleagues investigating a remarkable collection of fossils dug up in Hertfordshire, which date back 425 million years to the Silurian period.
They report their research in this month's American Scientist.
The fossils were preserved in nodules of rock and, remarkably, show soft appendages such as eyes, legs, antennae and gills.
Yet precisely because of the amazing 3D detail preserved in these tiny fossils conventional extraction using dentists drills, needles and chemicals wasn't possible.
After discussing all the options the team came up with a radical approach: grinding away thin layers of the fossils and recreating them as 3D computer models.
The fossil layers start out like the image on the left, which shows the ancient sea spider Haliestes.
'They're not even slices,' explains Derek. 'We grind off 20-30 microns taking photos every time we grind.'
Almost all soft bodied animals are 'flattened' before or during fossilisation. Yet this Haliestes fossil is one of the very few preserved in 'full 3D'. This has enabled the team to reconstruct it in unprecedented detail - it's the upper image of the two below:
'There are sea spiders swimming in our seas today,' Derek tells us [the lower of the two images above shows the living sea spider Nymphon]. 'However, in the fossil record there are less than 100 specimens of these ancient creatures and ours is quite possibly the oldest (seven larval specimens attributed to the sea spiders are known from older, Cambrian rocks, but this attribution has recently been doubted), and it is certainly fair to say the best preserved.'
The method, whilst destructive, makes it possible to extract much more scientific data from such deposits.
The hope is that this data will shed fresh light on the evolution of many species, helping us compare the fauna of millions of years ago with the animals we see around us.
*All fossil images are copyright Derek Siveter & colleagues, the team included Derek Briggs (Yale), David Siveter (Leicester) and Mark Sutton (Imperial).