Bivalves - British Geological Survey Skip to Content COVID-19 information News and events BGS Shop Hosted sites Skip to Content Search Button About BGS Overview Our work Annual reports Who we work with Geoscience solutions for net zero Government and policy Science briefing papers Our history Environmental policy and sustainability strategy Our team Staff profiles Senior Management Board BGS Board Science Advisory Committee Equality, diversity and inclusion at the BGS Organisational structure Our data and services General public Business services Business development Government and agencies OpenGeoscience Academic and researchers Digital data licensing and resellers GeoReports and online shop Our facilities Science facilities Library Conference facilities BGS Geology Shops Geological Walk BGS GeoSchool UK Geoenergy Observatories National Geoscience Data Centre National Geological Repository Working with us Careers at the BGS Job vacancies Working at the BGS Equality, diversity and inclusion at the BGS Contact us Offices and locations Customer feedback BGS Press Office BGS Intellectual Property Rights Freedom of information act Research Overview Explore our research projects Publications BGS University Funding Initiative Environmental change Groundwater research Urban geoscience Sea floor: marine geoscience Sea floor: scientific ocean drilling Soils and landscapes Geochemistry and health Centre for Environmental Geochemistry Decarbonisation Mineral resource security and flows Geo-disposal: radioactive waste Critical raw materials Geothermal energy Hydrocarbon systems Energy storage Carbon capture and storage Fluid and Rock Processes Laboratory Cluster Rock Volume Characterisation Laboratory Cluster UK Geoenergy Observatories Multi-hazards Volcanoes Earthquakes and seismology research Geomagnetism science capability Geodesy and Earth Observation Shallow geophysics Landslides research Shallow geohazards Digital geoscience Digital lab Hazard and resilience modelling 3D visualisation systems Product development Systems geology Citizen science Data National geoscience Global geoscience Official Development Assistance Partnerships for Development Integrated resource management in Eastern Africa Resilience of Asian cities Global geological risk International catchment observatories Science facilities Centre for Environmental Geochemistry Fluid and Rock Processes Laboratory Cluster Engineering and Geotechnical Capability Rock Volume Characterisation Laboratory Cluster Marine operations Geophysical observatories Data Overview Data search Datasets Energy datasets Geohazard datasets Land datasets Sea datasets Water datasets Map viewers Geology of Britain viewer GeoIndex (onshore) GeoIndex (offshore) UK Soil Observatory BGS maps portal Technologies Software Mobile apps Web services and APIs Web map services (WMS) Databases Geotechnical data services Collaborations Information hub Digital data licensing and resellers Publications Data collections Dictionaries BGS maps portal Scanned records Photographs and images Borehole records OpenGeoscience Photographs and images Mobile apps Software Scanned records Web services and APIs Data collections Publications Map data downloads Map viewers Digital data licensing and resellers Digital data product development National Geological Repository Accessing the NGR material collections NGR facilities Donations and loans of materials collections Palaeontology and biostratigraphy collections Borehole core collections NGR hydrocarbons (well samples) database National Geoscience Data Centre Deposit data with NGDC NGDC data management NGDC cited data National Hydrocarbons Data Archive Metadata abstract examples Archives Discovering Geology Overview Rocks and minerals Geological processes Landforms Relief Weathering Erosion Deposition Climate change What causes the Earth’s climate to change? Impacts of climate change The carbon story The greenhouse effect Understanding carbon capture and storage What are we doing about climate change? Earth hazards Earthquakes Understanding landslides Volcanoes Understanding sinkholes and karst Fossils and geological time Geological timechart Fossils Maps and resources Climate change through time Earth hazards resources Fossils and geological time resources Maps Postcard geology Search Search Clear Search Button Quick links Climate change Multiple hazards Decarbonisation ... Home » Discovering Geology » Fossils and geological time » Bivalves Bivalves Discovering Geology — Fossils and geological time Share this articleFacebookTwitterPinterestWhatsAppEmailCopy Link Bivalves have inhabited the Earth for over 500 million years. They first appeared in the midddle Cambrian, about 300 million years before the dinosaurs. They flourished in the Mesozoic and Cenozoic eras and they abound in modern seas and oceans; their shells litter beaches across the globe. Some also occur in lakes and rivers. Fossil bivalves were formed when the sediments in which they were buried hardened into rock. Many closely resemble living forms, which helps us to understand how they must have lived. The animal The geologists’ tool Myths and legends 3D fossil models Living bivalves — Xenostrobus pulex (little black mussel) — in New Zealand. © Avenue CC BY-SA 3.0. The animal Bivalves, which belong to the phylum Mollusca and the class Bivalvia, have two hard, usually bowl-shaped, shells (called valves) enclosing the soft body. The valves are the parts usually found as fossils, but decay of the elastic hinge tissue that joins them means that they are rarely preserved together. Anatomy of a bivalve shell. BGS © UKRI. Volviceramus involutus (J C Sowerby, 1828) has two very differently shaped valves. BGS © UKRI. Laevitrigonia gibbosa (J Sowerby, 1819) has valves that are mirror images. BGS © UKRI. Shape Bivalve shells may be elongate, round or highly irregular in shape. The valves are often mirror images, e.g. Laevitrigonia, but each can have a different shape, e.g. Volviceramus. Patterns of concentric and/or radial ribbing add strength and provide anchorage in sediment. Nodose (knobbly) ornaments may prevent shells being dislodged by water currents, while spines defend against predators or offer support on soft sediments. All forms have fine concentric lines marking shell growth. Crystal layers The valves consist of layers of crystals of the minerals calcite or aragonite. Particular strengths conferred by different crystal layer arrangements help bivalves adapt to a variety of environments. A hinge, formed by the interlocking of rows of projecting nodes (teeth) and notches (sockets) along one of the inside edges of each valve, guide the opening and closing of the valves. Protective shell The most important functions of fossil bivalve shells were to protect against predators and prevent dehydration in intertidal environments. The inside surface of a bivalve shell is marked by the attachment areas of the muscles and ligament responsible for opening and closing the valves. These features, with the teeth and sockets of the hinge, are important for classification. Bivalve environments and enemies Bivalves are vulnerable to attack from gastropods, crustaceans, starfish, fish and birds. Large, thick shells and spines protect some, while others hide themselves by burrowing into the sea bed using an extendable muscular ‘foot’. Insoluble layers in some bivalve shells resist the chemical attack of shell-boring gastropods. Bivalve environments and enemies: an artist’s impression of a seascape showing the different modes of life of modern and fossil marine bivalves. Mussels (1) and oysters (2) attach themselves to rocky surfaces, while burrowing (3 and 4) and rock-boring (5) bivalves hide beneath the seabed. Spiny shells (6) can deter some predators, while scallops (7) can escape by rapid flapping of their valves (8). The bowl-shaped shell of the Jurassic oyster Gryphaea (9) supported it on soft, muddy sea beds. ‘Enemies’ shown are fish, lobster, starfish and gastropod. BGS © UKRI. Shell shapes Penitella (Miocene to Recent), a rock-boring bivalve. © Geological Society of America/University of Kansas. Deltoideum (Jurassic) a type of oyster. BGS © UKRI. Pecten (Eocene to Recent) scallop. BGS © UKRI. Pholadomya (Triassic to Recent), a deep-burrowing bivalve. BGS © UKRI. Feeding habits Most bivalves live by filtering waterborne food particles, although some extract nutrients directly from the sediment. In the Mesozoic Era, the evolution of extendable tubes of soft tissue (siphons) enabled bivalves to burrow more deeply whilst keeping their food supply accessible. A special embayment of the inner shell margin (pallial sinus) allowed storage of the siphons when danger threatened. Reconstructed life position of Gryphaea arcuata (Lamarck, 1801) (Jurassic). BGS © UKRI. Modes of life Different modes of life are reflected by the shape of the bivalve shell. Streamlined burrowing forms contrast with the irregular form of oysters, e.g. Deltoideum that reflect the irregular surfaces they encrust. The bowl-shaped Gryphaea is adapted to resting on soft, fine-grained sediment, while Teredo and Penitella used their abrasive shell ornaments to bore respectively into wood and soft rocks. The rapid flapping of the fan-like shells of fossil scallops, e.g. Pecten, propelled them through the water to escape predators or to find new food. The geologists’ tool Bivalves can be used to show if the rocks in which they occur were formed in a marine, brackish or freshwater environment. For example, abundant fossil oysters might suggest deposition in shallow water or proximity to ancient shorelines. Sometimes, bivalves are a useful guide to the age of the rocks in which they occur. This is the case in the coal-bearing rocks of the Late Carboniferous in which Carbonicola has been used to identify and correlate individual coal seams. The strata of the Late Cretaceous Chalk Group, forming the famous White Cliffs of Dover, are rich in the remains of inoceramid bivalves. They have been used to refine the established Chalk biostratigraphy and so aid correlation. The strong influence of environmental factors on bivalve distribution coupled with rather slow rates of evolution limits their widespread use for biostratigraphy. Even in the rather uniform environment of the Chalk, some groups display faunal provincialism. Myths and legends The strongly recurved form of some Gryphaea is popularly known as the devil’s toenail. Some 17th and 18th century Scottish accounts show that its possession was believed to cure arthritis. In the old Scunthorpe coat of arms, images of this oyster signify its occurrence in the formerly commercially important Jurassic ironstone deposits of the area. Courtesy of the North Lincolnshire Council. Four-footed beasts Fossil bivalves can also resemble parts of ‘four-footed beasts’. Robert Plot (1640–1696) illustrated internal moulds of Jurassic specimens of Myophorella and Protocardia as horse’s heads and bull’s hearts respectively. ‘Horse’s head'(left); the bivalve Myophorella (right). Illustrated by Robert Plot. Courtesy of the National Museum of Wales, Department of Geology. ‘Bull’s heart’ (left); the bivalve Protocardia (right). Illustrated by Robert Plot. Courtesy of the National Museum of Wales, Department of Geology . 3D fossil models Cyprina sedgwickii (Cretaceous, Albian.) BGS © UKRI. Many of the fossils in the BGS palaeontology collections are available to view and download as 3D models. To view this fossil, or others like it, in 3D visit GB3D Type Fossils. Reference Woods, M A. 1999. Bivalves: fossil focus. (Nottingham, UK: British Geological Survey.) You may also be interested in Discovering Geology Discovering Geology introduces a range of geoscience topics to school-age students and learners of all ages. Show more Fossils and geological time Take a look at the history of the Earth, from its formation over four and a half billion years ago to present times. Show more Fossils What is a fossil and why do we study them? Explore the different methods of fossil preservation. Show more Was this page helpful? 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