2010-05-27 12:02:51
In 1963, two American paleontologists, J. Wyatt Durham, from the University of Berkeley, and KE Caster, from the University of Cincinnati, published in the prestigious journal Nature the description of Helicoplacus, the first representative of the helicoplacoids, a new class of echinoderms. fossils, the group that includes stars and sea urchins.
Helicoplacus is the oldest echinoderm that has been studied in depth. Its remains have been discovered in various places around the world, although complete specimens have only been found in the White Mountains of California. Helicoplacus lived in the Early Cambrian period, about 530 million years ago. It was an animal with a fusiform body, a few centimeters in length, shaped like a top or an inverted drop. Helicoplacus was covered by an armor of calcium carbonate plates, like those of all echinoderms, which were aligned in a spiral around the animal. The plates, although partially imbricated, were not articulated with each other, but were individually attached to the soft tissue, allowing the animal to expand and contract like an accordion. Unlike other echinoderms, Helicoplacus did not have pentaradial symmetry, in fact it was asymmetric. The ambulacral apparatus is formed by three branches that are arranged in the shape of a Greek i, also coiled helically around the body. As the calcium carbonate plates are practically the only fossil remains that have come down to us from Helicoplacus, and due to their mobility they usually appear displaced from their original position, there are still many unknowns about the anatomy of the animal; For example, it has not been possible to determine the location of the mouth, which could be in the center of the Greek i, at the junction of the three branches of the ambulacral apparatus, or at the upper end of it.
Helicoplacus was a marine animal. With its pointed end anchored in the gelatinous layer of microorganisms that covered the seabed at the beginning of the Cambrian, it obtained its food from suspended particles carried by currents. But around then, the first burrowing animals appeared, mainly worms and trilobites. By excavating the ground in search of food and protection, they favored the vertical mixing of the substrate with seawater, turning the ocean floor into a muddy sediment in which it was more difficult to find a solid foothold. This important environmental change is called the Agronomic Revolution or the Cambrian Substrate Revolution. Many life forms, such as Helicoplacus, were unable to adapt and became extinct.
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