Saturday, October 11, 2008

Collective Behavior in an Early Cambrian Arthropod

Collective Behavior in an Early Cambrian Arthropod. 2008. X.-G. Hou et al. Science 322: 224.

A unique set of fossils indicates that 525 million years ago marine animals congregated in Earth’s ancient oceans, most likely for migration, according to an international team of scientists.
From the press release

Fossil evidence of collective behaviour is extremely rare. But what makes the find even more intriguing is that it indicates that such behaviour was occurring at the beginning of the ‘Cambrian explosion’ – a major event that saw a vast profusion of complex organisms enter the fossil record for the first time.

'What we see in these fossils are shrimp-like animals with a carapace and segmented body, which are similar to arthropods that we know existed in the Cambrian seas,’ said Derek Siveter. ‘What’s unique about the Yunnan [China] fossil material is that it shows individual specimens closely interlocked to form a chain, of which there are several examples.’

These chains may have formed for reproductive purposes, or they may represent a stage in the animal’s life cycle – if so there are no comparable occurrences in modern arthropods.

The team believes the congregation is more likely to be evidence of migratory activity, possibly associated with animals congregating as a defence against predators.

The fossil was preserved in the Chengjian Lagerstatte, a fossil-rich exceptional preservation deposit discovered in 1984 that has been dated to the Lower Cambrian period, 525 million years ago, making it around 10 million years older than Canada’s famous Burgess Shale.