Small Shelly Fauna

The small shelly fauna or small shelly fossils, abbreviated to SSF, are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the Late Ediacaran and Early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.

Some of the fossils represent the entire skeletons of small organisms, including the mysterious Cloudina and some snail-like molluscs. However, the bulk of the fossils are fragments or disarticulated remains of larger organisms, including sponges, molluscs, slug-like halkieriids, brachiopods, echinoderms, and onychophoran-like organisms that may have been close to the ancestors of arthropods.

One of the early explanations for the appearance of the SSFs – and therefore the evolution of mineralized skeletons – suggested a sudden increase in the ocean's concentration of calcium. However, many SSFs are constructed of other minerals, such as silica. Because the first SSFs appear around the same time as organisms first started burrowing to avoid predation, it is more likely that they represent early steps in an evolutionary arms race between predators and increasingly well-defended prey. On the other hand mineralized skeletons may have evolved simply because they are stronger and cheaper to produce than all-organic skeletons like those of insects. Nevertheless it is still true that the animals used minerals that were most easily accessible.

Although the small size and often fragmentary nature of SSFs makes it difficult to identify and classify them, they provide very important evidence for how the main groups of marine invertebrates evolved, and particularly for the pace and pattern of evolution in the Cambrian explosion. Besides including the earliest known representatives of some modern phyla, they have the great advantage of presenting a nearly continuous record of Early Cambrian organisms whose bodies include hard parts.

Read more about Small Shelly Fauna:  History of Discovery, Occurrence, Mode of Preservation, Minerals Used in Shells, Evolution of Skeletons and Biomineralization, Evolutionary Significance

Famous quotes containing the words small and/or fauna:

    the small town big shot who, although very short,
    who although with a cigarette-stained mustache,
    who although famous for lobster on the rocks,
    left me here, nubkin, sucking in my vodka
    and emphysema cigarettes, unable to walk
    your walks, unable to write your writes.
    Anne Sexton (1928–1974)

    The whole fauna of human fantasies, their marine vegetation, drifts and luxuriates in the dimly lit zones of human activity, as though plaiting thick tresses of darkness. Here, too, appear the lighthouses of the mind, with their outward resemblance to less pure symbols. The gateway to mystery swings open at the touch of human weakness and we have entered the realms of darkness. One false step, one slurred syllable together reveal a man’s thoughts.
    Louis Aragon (1897–1982)