Fossil asteroids, the sea stars and ophuroids, the brittle stars, are found in the fossil record from the early Ordovician. The Ordovician groups show many similarities and can be difficult to distinguish.
Complete specimens are relatively rare and most fossils consist of arm segments or scattered individual plates. This is because, unlike echinoids (sea urchins) they do not have a rigid test. Their skeleton is composed of many small plates called ossicles and after death the skeletons disarticulate rapidly due to poor cohesion between these skeletal plates.
Echinoderms are stenohaline and their fossils are only found in sediments with a fully marine origin.
Scattered ossicles are relatively common in the Cretaceous Chalk Formation.
Where complete specimens do occur they often occur in abundance and there are three famous localities where they can be found.
1) The Devonian Bundenbach slates in Germany
2) The Jurassic lithographic Solnhofen limestone of Solnhofen in Germany which is famously the locality where Archaeopteryx was discovered.
3) The Jurassic 'Sea star Bed' of the Middle Lias Formation near Bridport, Dorset in England.
go on to modern forms
or return to specialised anatomy
Author: Elizabeth Sweet
Last updated: 22nd November 2005
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