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Post by Marsrocks on Feb 14, 2011 22:15:41 GMT -5
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Post by Marsrocks on Feb 14, 2011 22:23:15 GMT -5
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Post by Marsrocks on Feb 17, 2011 8:15:54 GMT -5
crinoid links: en.wikipedia.org/wiki/Crinoidwww.ucmp.berkeley.edu/echinodermata/crinoidea.htmlCrinoids, also known as sea lilies or feather-stars, are marine animals that make up the class Crinoidea of the echinoderms (phylum Echinodermata). They live both in shallow water and in depths as great as 6,000 meters. There are only a few hundred known modern forms, but crinoids were much more numerous both in species and numbers in the past. Some thick limestone beds dating to the mid- to late-Paleozoic are almost entirely made up of disarticulated crinoid fragments. # Fossilised crinoid columnals extracted from limestone quarried on Lindisfarne, or found washed up along the foreshore, which were threaded into necklaces or rosaries, became known as St Cuthbert's beads. # In the Midwestern United States, fossilized segments of columnal crinoids are sometimes known as Indian beads.[10] # Crinoids are the state fossil of Missouri. Crinoids are neither abundant nor familiar organisms today. However, they dominated the Paleozoic fossil record of echinoderms and shallow marine habitats until the Permo-Triassic extinction, when they suffered a near complete extinction: many Paleozoic limestones are made up largely of crinoid skeletal fragments. Stalked crinoids, or "sea lilies", lived attached to the bottom, and filtered food particles from the currents flowing past them. The earliest possible echinoderms appeared in the late Proterozoic, but there has been very little fossil material discovered until the early and middle Cambrian. Some paleontologists feel this is because early echinoderms were possibly soft bodied organisms and did not readily fossilize. Echinoderms began to appear in greater numbers during the early to middle Cambrian. The earliest fossil crinoid may have been Echmatocrinus, from the famous Burgess Shale of the middle Cambrian; some paleontologists, however, do not feel that Echmatocrinus was a true crinoid. By the beginning of the Ordovician many groups of echinoderms flourished, especially the crinoids. The crinoids were the most abundant group of echinoderms from the early Ordovician to the late Paleozoic, when they, along with the rest of the echinoderms, nearly went extinct during the Permo-Triassic extinction.Only a single genus of crinoid is known from the early Triassic, which eventually gave rise to the extant articulate crinoids. |
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Post by Marsrocks on Feb 17, 2011 8:21:28 GMT -5
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Post by Marsrocks on Mar 18, 2011 11:40:55 GMT -5
Segmentation is a common biological design:   |
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