(Image: Derek Siveter, Oxford University)
Four hundred and twenty-five million years ago, a strange creature shaped like a Christmas tree roamed the Earth – which makes it surprisingly young.
This 2-centimetre-long fossil arthropod, named Enalikter aphson, was found in rocks in Herefordshire, UK. It is the most recent addition to the megacheira, an extinct group of marine arthropods – and finding it in the 425-million-year-old rocks could indicate that megacheirans were distant ancestors of all arthropods alive today, including lobsters and spiders.
Soft-shelled animals like this don’t fossilise easily. But this one was exceptionally well preserved, nestled in a nodule of calcite inside the rock. It is the first time that a megacheiran has been seen in layers of rock younger than from the middle of the Cambrian period, which was between about 540 and 480 million years ago.
“It is incredible that it survived,” says Derek Siveter of the University of Oxford, who led the research. “The nodule acted like a womb.”
The researchers used a technique called optical tomography to examine the fossil in 3D. By imaging sequential slices of the fossil just 20 micrometres thick, they were able to build up this detailed portrait.
The image shows a creature only a couple of centimetres long. It has no eyes, a primitive tail and spiny limbs sticking out all along its body. A whip-like appendage by its mouth was probably used to catch marine animals even tinier than itself.
Journal reference: Proceedings of the Royal Society B, DOI: 10.1098/rspb.2013.2986