Description
Genuine Lower Bajocian Ammonite Association from Dorset
This carefully selected fossil specimen contains Lissoceras sp. and Hoplopleuroceras sp. ammonites preserved together within rock from the Bivalve Beds of the Inferior Oolite Group. It originates from the celebrated Horn Park Quarry near Beaminster, Dorset, UK, an internationally important Middle Jurassic fossil locality renowned for its exceptionally detailed ammonite succession.
The specimen represents marine life from the Lower Bajocian Stage of the Middle Jurassic Period. Each ammonite is identified to genus level, with “sp.” indicating that a precise species determination has not been assigned. The contrasting shell forms make this an especially interesting association piece for collectors interested in British ammonites, Jurassic palaeontology and fossil assemblages containing more than one ammonite genus.
Lissoceras Ammonite
Lissoceras was an ammonite genus characterised by a comparatively smooth, streamlined and involute shell. In involute ammonites, the later whorls overlap and conceal much of the earlier growth, leaving a relatively small central umbilicus. The flanks are generally smooth or only finely ornamented, while the outer margin, known as the venter, is rounded or blunt and lacks a prominent keel.
This restrained shell ornamentation gives Lissoceras a distinctive appearance when compared with heavily ribbed Bajocian ammonites. The genus is associated with the ammonite family Haploceratidae and the superfamily Haploceratoidea, within the extinct cephalopod order Ammonitida. Lissoceras is particularly significant to collectors because its elegant shell form provides a clear contrast with the more strongly ornamented ammonites found within many Inferior Oolite assemblages.
Hoplopleuroceras Ammonite
The accompanying Hoplopleuroceras sp. ammonite displays the more ornamented shell style typical of many Lower Bajocian ammonite groups. Features visible on an individual fossil depend upon preservation and the portion of the shell exposed, but ammonites of this general type are recognised by their coiled planispiral shells and more pronounced ribbing.
Having both a relatively smooth Lissoceras and a ribbed Hoplopleuroceras preserved within one specimen creates a visually and scientifically appealing contrast. The association demonstrates part of the ammonite diversity that inhabited the Jurassic seas covering southern Britain during the deposition of the Inferior Oolite sediments.
Inferior Oolite Group Geology
The Inferior Oolite Group is a major Middle Jurassic rock succession exposed across parts of southern and central England. In the Dorset and Somerset region, it includes varied bioclastic, sandy, ferruginous, peloidal and locally oolitic limestones, together with subordinate mudstones and other marine sedimentary rocks. These deposits preserve evidence of changing seabed conditions, water depths, sediment supply and marine communities over millions of years.
The term “oolite” refers to limestone containing ooids: small, rounded carbonate grains formed by the accumulation of calcium carbonate around tiny nuclei in agitated seawater. However, the Inferior Oolite Group is geologically varied, and not every bed is composed entirely of classic oolitic limestone.
The Bivalve Beds are named for the occurrence of fossil marine bivalves within this part of the succession. Ammonites found alongside these shelled organisms provide valuable evidence for correlating individual beds and reconstructing the sequence of Jurassic marine environments.
Horn Park Quarry Fossil Locality
Horn Park Quarry is regarded as one of Britain’s most important sites for studying the transition from the Aalenian into the earliest Bajocian. Its succession is exceptionally valuable because numerous ammonite-bearing horizons occur within a comparatively compact sequence of rocks.
The locality has produced a diverse and frequently well-preserved ammonite fauna, allowing palaeontologists to divide the succession into detailed biohorizons. Changes in ammonite species through the beds enable geologists to compare rocks of similar age across Britain and other parts of Europe. Horn Park has therefore become a key reference locality for Middle Jurassic ammonite biostratigraphy and the study of southern England’s Inferior Oolite deposits.
Jurassic Marine Cephalopods
Ammonites were extinct marine cephalopods related to modern squid, cuttlefish, octopuses and nautiluses. Their shells were divided internally into chambers. The living animal occupied the final chamber, while the older chambers helped regulate buoyancy through a connecting structure called the siphuncle.
During the Jurassic Period, ammonites evolved rapidly and became widespread throughout the world’s oceans. Their frequent evolutionary changes and broad geographical distribution make them exceptionally useful index fossils. Particular ammonite assemblages can identify narrow intervals of geological time, allowing separate rock exposures to be correlated with considerable precision.
An Authentic British Fossil for Display or Study
This genuine Lissoceras and Hoplopleuroceras ammonite fossil association is an excellent addition to a collection of British fossils, Dorset ammonites, Inferior Oolite specimens or Middle Jurassic marine life. Its combination of two ammonite genera, Lower Bajocian age and important Horn Park Quarry provenance gives it strong educational, geological and display interest.
This is a carefully chosen individual specimen. The photographs show the actual fossil you will receive, rather than a representative example. Natural variations, incomplete areas, matrix, mineral deposits, surface texture and small imperfections are authentic characteristics of a fossil that has survived within Jurassic rock for approximately 170 million years.
Full sizing is shown in the photographs.
This fossil is a 100% genuine specimen and includes a generic Certificate of Authenticity card with a lifetime guarantee.
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