Plagiostoma Fossil Bivalve Jurassic Lyme Regis Dorset UK Specimen – Charmouth Mudstone Formation Sinemurian Pliensbachian Bivalve Fossil

Description

Plagiostoma Fossil Bivalve from the Jurassic Coast of Lyme Regis

This genuine Plagiostoma sp. fossil bivalve originates from the renowned Charmouth Mudstone Formation at Lyme Regis, Dorset, United Kingdom, part of the internationally famous Jurassic Coast World Heritage Site. The fossil dates to the Lower Jurassic Period, spanning the Sinemurian to Pliensbachian stages, approximately 199–183 million years ago.

Bivalves belonging to the genus Plagiostoma were marine molluscs that thrived in Jurassic seas, inhabiting the soft sediments of shallow marine environments. Fossils of this genus are commonly found within Lower Jurassic strata and are recognised for their elegant shell morphology and distinctive radial ornamentation. Specimens from Lyme Regis are especially valued by collectors and geologists due to the site’s long history of fossil discovery and its exceptional preservation of marine life from the Early Jurassic.

This specimen represents a classic fossil from one of the most famous fossil localities in the world.

Geological Formation and Stratigraphic Context

The fossil comes from the Charmouth Mudstone Formation, a sequence of dark marine mudstones and shales deposited during the Early Jurassic along the margins of the ancient Tethys Ocean. These sediments accumulated in relatively calm offshore conditions, allowing fine muds to settle on the seabed and bury marine organisms that died and settled to the bottom.

The formation is particularly well exposed along the Dorset coastline between Lyme Regis and Charmouth, where coastal erosion continues to reveal new fossils. The Charmouth Mudstone represents part of the Lower Jurassic sedimentary succession that includes the famous Blue Lias and overlying Jurassic strata, which together preserve an exceptionally rich marine fossil assemblage.

Within these sediments, the remains of bivalves, ammonites, belemnites, marine reptiles, and fish have been preserved in remarkable abundance.

Classification and Biological Characteristics

Plagiostoma belongs to the phylum Mollusca, class Bivalvia, a group of marine invertebrates characterised by shells composed of two hinged valves. Within this class, Plagiostoma is placed in the order Pectinida, which includes scallop-like bivalves adapted for life on or within soft marine sediments.

Members of this genus were filter feeders, drawing water across their gills to extract microscopic food particles such as plankton and organic debris. This feeding strategy allowed them to thrive in nutrient-rich marine environments where suspended food was plentiful.

Bivalves played an important ecological role within Jurassic marine ecosystems, contributing to sediment stability and serving as prey for larger predators.

Shell Morphology and Distinctive Features

Fossils of Plagiostoma are recognised by their distinctive shell structure and symmetrical outline. Typical morphological features may include:

• Broad, rounded shell valves
• Distinct radial ribbing or ornamentation
• Well-defined hinge line connecting the two valves
• Growth lines marking stages of shell development

The shells were composed primarily of calcium carbonate and often preserved well within the fine-grained sediments of the Charmouth Mudstone. Over millions of years, mineralisation transformed these shells into fossils embedded within the surrounding rock matrix.

The preserved shell structure offers insight into the growth patterns and environmental adaptations of these Early Jurassic molluscs.

Early Jurassic Marine Environment

During the Sinemurian and Pliensbachian stages of the Early Jurassic, southern Britain lay beneath a shallow marine basin connected to the ancient Tethys Ocean. These warm seas supported a diverse range of marine organisms including ammonites, belemnites, crustaceans, fish, and marine reptiles.

Bivalves such as Plagiostoma lived on the seabed, forming part of the benthic community that occupied the marine floor. Their shells often accumulated in sediment layers following death, eventually becoming buried and fossilised.

The mudstone sediments of the Charmouth Formation created ideal conditions for fossil preservation, protecting delicate shells from erosion and allowing them to remain intact for nearly 200 million years.

Authentic Fossil Specimen

This fossil is a genuine Plagiostoma bivalve from the Charmouth Mudstone Formation of Lyme Regis, Dorset, UK. The specimen has been carefully selected for quality and display appeal.

The photograph shows the actual fossil specimen you will receive, ensuring transparency and authenticity for collectors.

Full sizing please see photo.

Certificate of Authenticity

This fossil includes a Certificate of Authenticity lifetime guarantee generic card, confirming that the specimen is a genuine natural fossil.

Fossils from Lyme Regis are internationally recognised for their scientific importance and historic significance. A Plagiostoma bivalve from the Charmouth Mudstone Formation represents a classic Early Jurassic fossil and a fascinating piece of the ancient marine ecosystems preserved along Britain’s Jurassic Coast.