Fossil blob hints at our ancient ancestors
16 August 2010, by Adele Walker
Scientists have identified the fossil of a previously undocumented ancient creature – a primitive relative of the brachiopods that lived around 425 million years ago.
3-D digital image of Drakozon kalumon
Though just a couple of millimetres long, it has features that hint at possible details of the ancient ancestors of all animal life.
Brachiopods are bivalved sea creatures – they have a two-part hinged shell. But this organism, which the researchers have named Drakozon kalumon, had no hard shell.
It was preserved when it was entombed in volcanic ash under the sea. The animal itself then decayed and was replaced by calcite crystals.
A team of researchers from the UK and US found the 1.7mm-long fossil attached to the fossil of a shelled brachiopod, when they cracked open a nodule of Herefordshire Lagerstätte rock, from near the Welsh border.
They took microscopically thin sections through the sample and photographed them to construct a digital 3-D image. This enabled them to examine the fossil in detail from all angles.
'This is particularly important because of what it could tell us about the ancestors of all animals'
Dr Mark Sutton, Imperial College London
The researchers describe the creature in Biology Letters. It is identified as a lophophorate, which means it fed through a lophophore – a pair of tentacles that surrounded its mouth.
Though it didn't have a shell, D. kalumon had a 'hood' on one side which the researchers interpret as being related to the dorsal valve of a shelled brachiopod. The attachment, which joined it to its host's shell, was a possible precursor of a ventral valve.
But the most significant details are a series of ridges and furrows that suggest it had a serial structure, with a series of repeated 'sections' – a caterpillar would be an extreme example. Later brachiopods do not have this serial structure.
'This is particularly important because of what it could tell us about the ancestors of all animals,' says Dr Mark Sutton of Imperial College London, lead author of the report. 'There are hints in the fossil record and from the study of living animals that their common ancestor built itself in this way. New evidence of serial construction in a primitive lophophorate is another hint in that direction.'
The fossil adds to our knowledge of the different types and ecological range of lophophorates from this period. But, according to Sutton, 'it could be just the tip of the iceberg.'
'We don't know very much at all about soft-bodied lophophorates from this era. The fact that these creatures haven't been found anywhere else most likely reflects their low preservation rates,' says Sutton.
'In fact, there may have been all sorts of different types, they could have been widespread at this time,' he concludes.
The 'articulate' brachiopod Bethia to which D. kalumon was attached was identified by the same research team as being the first known to have fossil soft parts, and was reported in Nature in 2005.
MD Sutton, DEG Briggs, David J Siveter, Derek J Siveter, A soft-bodied lophophorate from the Silurian of Englnad. Biology Letters doi: 10.1098/rsbl.2010.0540
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