The conga was the world鈥檚 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 , 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.
鈥淚t鈥檚 showing that, 525 million years ago, we鈥檝e got really quite sophisticated and potentially complex interaction between different animals,鈥� says , of the University of Oxford, who analysed the fossil along with colleagues at the University of Leicester, UK.
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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.
鈥淲e 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,鈥� 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鈥檚 mouth appears blocked by its neighbour鈥檚 tail.
鈥淭he simplest explanation for this is that it is some kind of collective behaviour coming together for migration, perhaps associated with defence in numbers,鈥� he says.
, 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 鈥渟napshot scenes of 鈥榥ormal鈥� life鈥� in the Cambrian, he says.
鈥淔inding an example of collective behaviour so long ago is really eye opening to us,鈥� 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.
鈥淐ollective behaviour is all around us and it鈥檚 also within us, the function of cells within in the body is a form of collective behaviour.鈥�
Journal reference: (DOI: 10.1126/science.1162794)
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