Fossil Sea Urchin Calcified

Description

An echinoderm is a member of the phylum Echinodermata which contains a number of marine organisms recognized by their pentamerous radial symmetry, calcareous endoskeleton, and a water vascular system which helps operate their small podia. Podia are small extensions of flesh which are operated by water pressure and muscles, and controlled by the nervous system of the echinoderm. The calcareous endoskeleton is made of many small plates that overlap under the skin, forming an armor and a structural form for the organisms. Examples of an echinoderm include a starfish, a sand dollar, a brittle star, a sea urchin, and a sea cucumber. There are around 7,000 echinoderm species, and they can range from less than an inch to over three feet in diameter

Echinoid fossils are the fossilized remains of sea urchins, spiny marine invertebrates that live on the seabed. Humans have been interested in these fossils for millennia, have considered them lucky, have imbued them with magical powers and linked them to their deities.
The main feature of echinoid fossils is the set of five ambulacra on the test radiating out from a central point, forming a distinctive five-petalled pattern. The earliest echinoid fossils date from the late Ordovician period, some 450 Mya. The group has a rich fossil record, their hard tests made of calcite plates and their spines being found in rocks from every period since then. Echinoids from the Paleozoic era had thin tests and their fossils are often incomplete, consisting of groups of plates or isolated spines. Later echinoids had more robust tests and fossilized well, usually with the spines detached from the test.[4] Fossils of echinoids are common in rocks from the Jurassic and Cretaceous age, especially from late Cretaceous chalk. In the White Cliffs of Dover in southern England, the echinoid fossils that are present can be used for dating the various chalk strata in which they occur. This is because they are relatively abundant and well-preserved compared to other fossilized animals and can be differentiated by type between different ages.