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Newly Found Fossils Show Origin Of ‘Curling Up’ Defensive Strategy

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Rolling in the deep past: a struggle for life.

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You’re under attack! Quick, what do you do? One of the options is to curl up and protect your vulnerable parts, to roll your body into a little ball and prevent as much damage as you possibly can. From woodlice to hedgehogs, this is a defensive strategy that’s widely used throughout the animal kingdom. Now, a new discovery, published in Biology Letters, exposes the earliest known example of this behavior.

Researchers from Cambridge University and the Chinese Academy of Sciences have found rolled up trilobite fossils of about 510 million years old, predating remnants of other curled up critters by several millions of years. The unearthed fossils of small olenellid trilobites show the first steps towards the refinement of the ‘curling up’ defensive strategy, eventually leading to what is known as encapsulating enrolment in their later cousins.

The symmetrical curling and perfect articulation of body segments are strong hints that the fossils weren’t just squashed together, but in fact represent an early snapshot of the implementation of what would become a highly efficient way of bodily resistance against attackers. Indeed, later trilobites, roaming ancient seas filled with ferocious predators, would go on to perfect the technique and become able to encapsulate themselves completely. The development of body segments that covered each other more effectively and a large tail shield, coupled with locking mechanisms that prevented them from being pried apart easily, meant that these later trilobites could fully cover their precious heads and protect their vulnerable legs.

These newly found older fossils, however, did not possess the improvements mentioned above. They probably relied on good old muscle power to remain rolled up. After death, their muscles would relax and they’d unroll again, which explains why it’s been so hard to find early evidence of the curling up ability. Only early trilobites that were covered quickly after their demise in a defensive, rolled up position would leave a fossil trace like the one discovered by the researchers, providing us with glimpse of life in the dangerous early seas and the arms race between prey and predator that took place there.

Reference

Photo: Flickr, FurLined
Source: Ortega-Hernández J, Esteve J, & Butterfield NJ (2013). Humble origins for a successful strategy: complete enrolment in early Cambrian olenellid trilobites. Biology letters, 9 (5) PMID: 24068021

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