Description
Genuine Micraster decipiens Fossil from Eastbourne
This carefully chosen fossil is a genuine specimen of Micraster decipiens, an extinct irregular echinoid commonly known as a heart urchin. It originates from the Chalk Group deposits around Eastbourne, East Sussex, United Kingdom, and dates from the Coniacian Stage of the Upper Cretaceous.
The Coniacian extended from approximately 89.8 to 86.3 million years ago, when southern Britain was submerged beneath a warm, extensive marine sea. This fossil is therefore a tangible remnant of an ancient ecosystem that existed nearly 90 million years before the present day.
The listing photographs show the actual fossil specimen you will receive. Please refer to the photographs for the full dimensions, scale, colour, preservation and condition. Natural variations in shape, surface detail, chalk matrix, mineral staining and weathering are part of the specimen’s individual geological character.
Fossil Species and Scientific Classification
Micraster decipiens belongs to the phylum Echinodermata, class Echinoidea, order Spatangoida and family Micrasteridae. It was formally described by the French palaeontologist Émile Bayle in 1878.
The genus Micraster contains some of the most recognisable and scientifically important echinoids found in the British Chalk. These animals were related to modern sea urchins but had evolved an irregular, bilaterally symmetrical body adapted for directional movement and burrowing within soft seabed sediment.
Micraster decipiens has frequently been associated with the older name Micraster cortestudinarium in British geological literature. Detailed studies of test shape, ambulacral structure and stratigraphic distribution helped palaeontologists distinguish M. decipiens as a characteristic Coniacian form. The species is particularly important in the study of evolutionary changes within the Micraster lineage.
Distinctive Heart Urchin Morphology
The fossilised shell of an echinoid is known as the test. In Micraster decipiens, the test is typically broad, heart-shaped or rounded in outline, with a domed upper surface and a flatter underside.
A pronounced anterior groove runs down the front of the test and helped channel oxygenated water towards the animal while it lived beneath the sediment. Five ambulacral areas extend across the test, with the paired upper ambulacra forming petal-like structures. Rows of small pores within these areas allowed specialised tube feet to pass through the test.
The mouth was positioned towards the front of the lower surface, while the anal opening was located at the posterior. This separation reflects the animal’s directional mode of movement. Depending on preservation, the specimen may display its characteristic outline, anterior groove, ambulacral petals, pore pairs, plate boundaries or natural openings.
Coniacian Chalk Group Geology
Eastbourne and the neighbouring East Sussex coastline contain internationally important exposures of the Chalk Group. These white limestone deposits accumulated in the north-west European Chalk Sea during the Late Cretaceous.
The chalk is composed predominantly of microscopic calcium-carbonate plates produced by marine plankton known as coccolithophores. After these organisms died, their remains settled onto the seabed as extremely fine carbonate mud. Continuous accumulation, burial and compaction eventually transformed the sediment into the chalk exposed today.
The Coniacian succession around Eastbourne includes strata within the White Chalk Subgroup, particularly the Lewes Nodular Chalk Formation. This formation is characterised by hard nodular chalk, softer chalk beds, marl seams, hardgrounds and bands or nodules of flint. These distinctive horizons enable geologists to correlate individual parts of the coastal succession across East Sussex and southern England.
Micraster decipiens Biozone
Micraster decipiens is associated with an important interval of the lower Coniacian Chalk. In traditional British terminology, much of this succession was assigned to the Micraster cortestudinarium Zone. Later palaeontological work recognised an upper Micraster decipiens Zone of Coniacian age, reflecting the importance of this species for distinguishing and correlating particular fossil-bearing horizons.
The evolutionary sequence preserved by Micraster fossils is especially valuable to biostratigraphy. Through successive chalk beds, changes can be observed in the height and outline of the test, the development of the anterior groove, the form of the ambulacra and the position of the mouth. These changes allow specialists to compare geographically separated exposures and establish their relative geological ages.
Ancient Chalk-Sea Environment
During the Coniacian, the Eastbourne area lay beneath a warm, relatively deep sea with little sand or terrestrial mud entering the basin. The seabed consisted largely of soft, pale carbonate sediment.
This environment supported echinoids, ammonites, bivalves, brachiopods, sponges, bryozoans, crinoids, fish and sharks. Micraster decipiens lived partly or completely buried beneath the sediment surface. Its tube feet and fine spines assisted with movement, respiration and the collection of organic food particles.
Water was drawn along the anterior groove and circulated through the animal’s burrow, supplying oxygen while waste was directed towards the posterior. This specialised infaunal lifestyle provided protection from predators and enabled Micraster to exploit nutrients within the soft chalk mud.
Authentic British Fossil with Certificate of Authenticity
This genuine Upper Cretaceous echinoid is ideal for fossil collectors, geology enthusiasts, educational displays, natural-history cabinets or anyone interested in the famous Chalk geology of Eastbourne and East Sussex.
The fossil includes a generic Certificate of Authenticity card carrying a lifetime guarantee of authenticity. It has been individually selected for its natural appearance, geological interest and collectable character. The listing photographs show the exact specimen you will receive, and full sizing can be seen in the photographs.
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