The shell was a groundbreaking biological invention, acting both as a support and as protection from

The shell was a groundbreaking biological invention, acting both as a support and as protection from prey. But how exactly did the first shells appear, and what did they look like? This was a difficult question in palaeontology for many years - ancient rocks contained only ghostly imprints of soft-bodied creatures, and shelled fossils seemed to simply appear in the fossil record, fully formed, at the start of the Cambrian (540 million years ago). Their ancestry remained a mystery until the discovery of an odd fossil assemblage in rocks dating from just before the Cambrian period began. These creatures have been nicknamed the SSF, or small shelly fauna.The small shellies appear at the end of the Ediacaran period (the late Precambrian). They form a diverse and non-specific group, with tubes, plates and spikes being the most common forms - dissociated parts of complex skeletons like those of sea urchins, sponges and other armoured slug-like beasts. Some of the earliest shellies are single shells, however, like the tubular Cloudina and some coiled specimens linked to the early molluscs (Helcionellids). There are no close genetic ties between different types of small shelly fossils, however, and the definition of the group is fairly arbitrary. Most of the fossils unique to the small shelly fauna disappear soon after the dawn of the Cambrian.As well as being the earliest examples of mineralised skeletons known, the SSF may hold the key to an even bigger event in the history of life. Some specimens of Cloudina have been found with tiny holes cut through them, and scientists have argued that this may represent the earliest trace of predation, one animal actively feeding upon another. The shells themselves could very well be a wider adaptation to protect organisms from the newly evolved killers, the first step in the evolutionary ‘arms race’ between predator and prey.-TJTThe photo shows Cloudina specimens, some with possible predator borings. It was released along with this paper on the discovery : http://bit.ly/1MuJxi0 -- source link

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