Fossilised shrimp show earliest group behaviour
- 19:00 09 October 2008
- NewScientist.com news service
- Ewen Callaway
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The conga was the world's first dance, it seems. A newly discovered caravan of crustaceans from half a billion years ago shows that group behaviour evolved not long after animals themselves.
Palaeontologists led by Hou Xian-Guang, of Yunnan University, China, discovered fossilised chains of up to 20 crustaceans linked head-to-toe, the earliest record of any collective animal behaviour and perhaps an adaptation to a migratory ocean lifestyle.
"It's showing that, 525 million years ago, we've got really quite sophisticated and potentially complex interaction between different animals," says Derek Siveter, of the University of Oxford, who analysed the fossil along with colleagues at the University of Leicester, UK.
They concluded that the undulating procession of ancient arthropods, each about 2 centimetres long, represents more than a quirk of fossilisation. Though none of their arms, legs or antennae survived a half billion years in stone, the animals probably interlocked appendages to stay together.
"We hypothesise that the chain was in the water column and it met its demise by whatever reason or forces, then it sunk to the bottom," he says.
Modern creatures called tunicates, or sea squirts, form long chains to boost mating opportunities, but Siveter doubts that his crustaceans engaged in a carnal dance because no modern crustaceans show this behaviour. Group feeding is off the table, too, because each animal's mouth appears blocked by its neighbour's tail.
"The simplest explanation for this is that it is some kind of collective behaviour coming together for migration, perhaps associated with defence in numbers," he says.
Nigel Hughes, a palaeobiologist at the University of California, Riverside, agrees that the parade represents more than the death throes of ancient arthropods. Rather, the fossils provide "snapshot scenes of 'normal' life" in the Cambrian, he says.
"Finding an example of collective behaviour so long ago is really eye opening to us," says Iain Couzin, a biologist at Princeton University. He and colleagues are now creating computer models to understand the evolution of group action, which seems to arise often and with little individual complexity needed.
"Collective behaviour is all around us and it's also within us, the function of cells within in the body is a form of collective behaviour."
Journal reference: Science (DOI: 10.1126/science.1162794)
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