Crinoids! If you spend any time looking at carbonate rocks in the U.S. or Europe, and probably in ot

Crinoids!If you spend any time looking at carbonate rocks in the U.S. or Europe, and probably in other areas around the world, you’re likely to run into a lot of these critters. These are segments of crinoid stems, the remnants of a number of species that are nearly extinct today but once dominated the ocean floor environments.Crinoids are animal species; echinoderms, the same phylum that today contains animals like starfish and sea urchins. Despite being animals, their behavior seems a lot like plants.Crinoids are filter-feeding organisms that lived on the ocean floor. They attach themselves to the ocean floor and grow long stalks upwards. Some crinoids could have been more than a meter tall on the ocean floor. They grew upwards until they stood above other species, allowing them to filter food out of the passing ocean waters.Occasionally crinoids are found in-tact, with the full stalk still hooked together, but much more common is this type of fossil. These are segments of the stalk of the crinoid. The stalk is built up of many of these segments hooked together, all made out of calcium carbonate; the organism grew as a tower of these stem segments. When they die, the stems commonly break apart, dispersing dozens, if not hundreds of segments out into the nearby environment. Consequently, rocks from the age dominated by crinoids are often absolutely loaded with these segments.These crinoids are about 165 million years old and come from the Wiltshire area in the United Kingdom. The lines that began evolving into the crinoids likely began during the Cambrian and similar species are represented within the Burgess Shale fauna. They dominated the seas of the Paleozoic from the Ordovician on, but most species nearly went extinct during the end-Permian mass extinction. Since then, crinoids have become much rarer in the ocean; only a single species is known from the early Triassic. These particular crinoids and the ones alive today are likely descendents of that single surviving species.-JBBImage credit: Wednesbury Museum & Art Gallery, shared under creative commons licensehttp://www.flickr.com/photos/41006267@N06/5029090765/http://geologymatters.org.uk/collections/getrecord/WEDSD_Geology_Temp_13/Read more:http://www.ucmp.berkeley.edu/echinodermata/crinfoss.htmlhttp://www.oceanicresearch.org/education/wonders/echinoderm.html -- source link

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