This carefully chosen fossil is a genuine specimen of Sphaeroidothyris sp., an extinct marine brachiopod from the Inferior Oolite Group at Horn Park Quarry in Dorset, England. It dates from the Bajocian Stage of the Middle Jurassic and represents an animal that inhabited a warm, shallow sea approximately 170 million years ago.
The listing photographs show the actual fossil specimen you will receive. This is not a stock photograph or a randomly selected example. Please examine the images carefully for the fossil’s complete dimensions, proportions, colour, preservation, natural surface features and any associated limestone matrix. Full sizing is shown in the photo.
Sphaeroidothyris is a genus of brachiopod belonging to the phylum Brachiopoda, class Rhynchonellata and order Terebratulida. The genus is placed within the family Loboidothyrididae in current taxonomic databases.
The identification Sphaeroidothyris sp. means that the specimen can be assigned confidently to the genus Sphaeroidothyris while retaining the scientifically appropriate identification at genus level.
Brachiopods are exclusively marine, filter-feeding animals protected by two mineralised shell valves. Although they can resemble bivalve molluscs such as clams, oysters and mussels, brachiopods belong to a completely different animal phylum. A bivalve shell is arranged on the left and right sides of the body, whereas a brachiopod possesses dorsal and ventral valves positioned above and below the animal.
The two valves were joined along a hinge and opened slightly while the animal was feeding. The soft body remained protected inside the shell, with only a limited opening required to circulate seawater through the mantle cavity.
Sphaeroidothyris brachiopods are noted for their rounded, inflated shell form. The genus name reflects this broadly spheroidal appearance. A typical specimen may have a smooth to finely marked exterior, a curved profile and two unequal valves that together create a compact, biconvex shape.
The larger ventral valve may preserve a projecting beak near the hinge. In life, an opening in this region accommodated the pedicle, a muscular stalk used to secure the brachiopod to a shell fragment, stone or other stable object on the seabed.
Growth lines may be visible across the shell surface. These formed as new shell material was added around the margin throughout the animal’s life. The front edge, where the valves met, may also show gentle folding or asymmetry associated with the shell’s mature growth.
The animal fed using a specialised ciliated organ called a lophophore. This structure generated water currents and captured microscopic organic particles suspended in the seawater. Internal supports helped hold the lophophore in position, although these structures are normally concealed inside a complete fossil shell.
Any limestone matrix, mineral staining, natural fractures, weathered surfaces, small chips or incomplete areas visible on the specimen are genuine features resulting from burial, fossilisation, geological exposure and preparation. They contribute to its unique appearance and geological character.
The Inferior Oolite Group is a varied succession of Middle Jurassic sedimentary rocks. In Dorset and Somerset, it includes bioclastic, peloidal, sandy, ferruginous and bioturbated limestones, together with smaller quantities of oolitic limestone, sandstone, limestone conglomerate, lime-rich mudstone and mudstone.
The term “oolite” refers to limestone containing ooids, which are small, rounded carbonate grains formed as calcium carbonate accumulated in layers around tiny particles in warm, agitated seawater. The word “Inferior” does not describe the quality of the stone. It indicates that these rocks occur stratigraphically beneath the younger Great Oolite succession.
The Inferior Oolite of Dorset accumulated in a shallow shelf sea where sediment deposition was often slow. The resulting succession is relatively condensed, meaning that comparatively thin rock layers can represent substantial intervals of geological time. Reworking by currents, pauses in deposition, seafloor erosion and biological disturbance all contributed to the character of these fossil-rich limestones.
The Bajocian is the second of the four stages forming the Middle Jurassic, following the Aalenian and preceding the Bathonian. Horn Park Quarry preserves an important succession spanning Aalenian and Bajocian rocks within the Inferior Oolite Formation.
During the Bajocian, the area that would eventually become Dorset lay beneath a warm epicontinental sea. Marine conditions supported diverse communities of brachiopods, ammonites, bivalves, gastropods, echinoids, crinoids and other invertebrates.
Sphaeroidothyris lived on the seabed as part of this benthic community. Its lophophore filtered suspended food from the water, while its compact shell protected the soft animal from physical disturbance and potential predators.
After the brachiopod died, its shell settled onto the Jurassic seabed. It may have remained complete or become moved by currents before being covered by carbonate sand, shell debris and lime-rich mud.
Burial protected the shell from complete destruction. As additional sediment accumulated, pressure compacted the deposit and calcium-carbonate cement bound the particles together, gradually producing limestone. Mineral-rich groundwater could fill internal spaces or alter portions of the original shell while retaining its recognisable form.
The fossil may preserve original calcitic shell material, recrystallised mineral matter, an internal mould or a combination of preservation styles. Its present appearance records both the anatomy of the original brachiopod and the geological processes that acted upon it after burial.
Horn Park Quarry is situated near Beaminster in Dorset and is one of Britain’s best-known Aalenian–Bajocian geological localities. Its highly fossiliferous Inferior Oolite succession has produced thousands of fossils and has played an important role in research into Middle Jurassic stratigraphy and ammonite biostratigraphy.
The quarry is protected for its geological importance and is recognised as a reference locality for studying the sequence of rocks and fossils formed during this part of the Jurassic. A specimen with recorded genus, geological group, stage and locality is especially suitable for a documented British fossil collection, educational display or specialist Jurassic cabinet.
You will receive the exact Sphaeroidothyris sp. brachiopod fossil shown in the listing photographs. The specimen has been individually selected for its natural appearance, geological provenance and collectable character.
This genuine fossil includes a generic Certificate of Authenticity card supported by a lifetime authenticity guarantee. It is an authentic prehistoric specimen rather than a cast, replica or artificially manufactured reproduction.
This Middle Jurassic brachiopod makes an excellent addition to a British fossil collection, Jurassic display, brachiopod collection, geology cabinet or educational reference set. It would also make a distinctive natural history gift for a fossil collector, palaeontology student, geology enthusiast, teacher or anyone fascinated by Britain’s ancient marine environments.