Description
Genuine Stereocidaris Fossil Echinoid Spine
This carefully selected fossil is a genuine Stereocidaris sp. echinoid spine from the Chalk Group of Thanet, Kent, UK. Dating from the Santonian Stage of the Upper Cretaceous, approximately 83.6 to 86.3 million years ago, this remarkable fossil represents one of the defensive spines belonging to an extinct cidaroid sea urchin that inhabited the warm tropical seas covering southern Britain during the Late Cretaceous.
The listing photographs show the exact fossil specimen you will receive. This is not a stock image or representative example. Please examine the photographs carefully for the spine’s preservation, natural surface ornamentation, colour, condition and any remaining chalk matrix. Full sizing and scale information can be found in the photographs.
Fossil Identification and Classification
Scientific identification: Stereocidaris sp.
Fossil type: Echinoid spine
Kingdom: Animalia
Phylum: Echinodermata
Class: Echinoidea
Subclass: Cidaroidea
Order: Cidaroida
Family: Cidaridae
Genus: Stereocidaris
Geological period: Upper Cretaceous
Stage: Santonian
Rock unit: Chalk Group
Locality: Thanet, Kent, United Kingdom
The designation “sp.” indicates that the fossil has been confidently assigned to the genus Stereocidaris, although the individual species cannot be determined with certainty from the preserved material alone. Isolated cidaroid spines are common finds within the British Chalk and are highly sought after by collectors due to their distinctive appearance and excellent preservation.
Morphology of Cidaroid Echinoid Spines
Unlike irregular echinoids, cidaroid sea urchins possessed a spherical test covered with relatively few but exceptionally large and robust primary spines. These spines were attached to prominent tubercles on the test by a ball-and-socket style articulation, allowing considerable movement while providing effective protection from predators.
Stereocidaris is recognised for producing thick, solid calcitic spines that often display longitudinal ridges, finely ornamented surfaces, delicate granulation or subtle striations depending on the individual species and degree of preservation.
The spine itself consists of a widened basal collar where it attached to the echinoid’s test, gradually tapering toward the distal tip. Depending on preservation, this specimen may exhibit growth lines, surface sculpture, natural weathering, mineral staining and fine structural details formed during the animal’s life.
Because echinoid spines frequently became detached after death, isolated examples are considerably more common than complete sea urchins. Their durable calcite composition allowed many to survive burial and fossilisation remarkably well.
Natural variations including minor abrasion, small chips, chalk adhesion, mineral staining or weathered surfaces are entirely normal features of authentic fossil echinoid spines and add to the individuality of each specimen.
Chalk Group Geology of Thanet
Thanet, situated on the northeastern coast of Kent, is well known for its extensive Upper Cretaceous Chalk exposures. These deposits form part of the extensive Chalk Group that stretches across southern England and records millions of years of continuous marine sedimentation.
The Chalk Group consists predominantly of soft white limestone composed almost entirely of microscopic calcite plates produced by marine coccolithophores. As these planktonic algae died, their skeletal remains slowly accumulated across the floor of a broad, warm sea. Over countless generations this carbonate sediment compacted to form the thick chalk sequences exposed around the Kent coastline.
The Santonian Chalk represents deposition during a period of exceptionally high global sea levels. Sedimentation occurred far from major river systems, allowing remarkably pure carbonate mud to accumulate with very little terrestrial input. Flint nodules, marl seams and occasional hardgrounds record changes in sedimentation and post-depositional chemical processes throughout the Chalk succession.
The fine-grained nature of the chalk created ideal conditions for preserving delicate marine fossils, including echinoids, sponges, brachiopods, bryozoans, bivalves, ammonites and countless microscopic organisms.
Santonian Marine Environment
During the Santonian Stage, southern Britain lay beneath a warm subtropical sea that supported one of the richest marine ecosystems of the Late Cretaceous. Clear, nutrient-rich waters encouraged abundant plankton growth, forming the foundation of a complex food web.
Cidaroid echinoids such as Stereocidaris lived upon the seafloor where they moved using hundreds of tube feet working together with their articulated spines. Unlike many irregular echinoids that burrowed through sediment, cidaroids generally crawled across firmer substrates searching for food.
Modern relatives feed upon algae, encrusting organisms, detritus and other organic material, and fossil Stereocidaris likely occupied a similar ecological niche. Their large movable spines provided defence against predators while also helping maintain stability across the seabed.
Following the death of the animal, the connective tissues holding the spines rapidly decayed, causing the spines to separate from the test. These detached spines settled into fine carbonate mud where rapid burial protected them from destruction. Over millions of years, mineralisation and lithification preserved the calcite spine as part of the fossil record.
Fossil Preservation
Cidaroid spines are among the most recognisable echinoid fossils recovered from the British Chalk. Their dense calcitic construction enabled them to withstand burial remarkably well, often preserving exceptionally fine surface ornamentation.
Many specimens remain almost unchanged from their original skeletal structure, while others exhibit natural recrystallisation or subtle mineral replacement. Each spine preserves evidence of the biology of the original animal as well as the geological processes that affected it throughout tens of millions of years.
Every fossil displays unique characteristics resulting from its individual history of growth, burial, fossilisation and weathering. No two specimens are identical.
Collectable British Cretaceous Echinoid Fossil
This genuine Stereocidaris spine combines an identifiable cidaroid echinoid with the famous Santonian Chalk deposits of Thanet, making it an excellent addition to any British fossil collection, echinoid display, geological cabinet or educational collection.
It is equally suitable as a gift for fossil collectors, geology students, palaeontology enthusiasts, museum educators or anyone fascinated by prehistoric marine life. Isolated echinoid spines are particularly attractive display fossils because they preserve intricate natural detail while representing an important component of ancient Cretaceous ecosystems.
Actual Specimen and Full Sizing
The fossil shown in the listing photographs is the exact specimen you will receive. It has been carefully selected for its preservation, natural detail and geological significance.
Please refer to the photographs for full sizing. The images provide the most accurate representation of the specimen’s dimensions, condition, preservation, visible ornamentation and any remaining chalk matrix.
Certificate of Authenticity and Lifetime Guarantee
This fossil is a genuine natural specimen and includes a generic Certificate of Authenticity card with a lifetime authenticity guarantee. The certificate confirms that the item is supplied as a real fossil rather than a modern cast, replica or artificial reproduction.
The specimen will be carefully packaged to ensure it arrives safely and is ready for display or addition to your fossil collection.
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