The Trigoniidae represent a large and morphologically interesting family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of highly ornamented non-siphonate bivalves. They originated from the Myophoriidae in the Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...

 and underwent an explosion of diversity in the Jurassic
The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

, reaching an acme in the Cretaceous
The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

, although most genera
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

 became extinct at the end of this period. The most striking feature of the Trigoniidae, which has attracted attention for centuries, is their external ornament. This is usually present as ribs or costae or rows of aligned tubercles. Although they were abundant in the Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 era, they are today represented by only one living genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...

, Neotrigonia, which inhabits waters off the coast of southern Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...


Neotrigonia - the discovery of a living genus

Before the beginning of the nineteenth century, no trigoniid had been described from rocks younger than the Cretaceous Period. In 1802, however, Francois Peron
François Péron
François Auguste Péron was a French naturalist and explorer. He is credited with the first use of the term anthropology.-Explorations:...

 discovered a living species in waters off the coast of Tasmania
Tasmania is an Australian island and state. It is south of the continent, separated by Bass Strait. The state includes the island of Tasmania—the 26th largest island in the world—and the surrounding islands. The state has a population of 507,626 , of whom almost half reside in the greater Hobart...

. Lamarck named it Trigonia margaritacea in 1804 with Cossmann renaming the genus Neotrigonia in 1912. Today, five living species have been identified, and are all found off the coast of Australia. Neotrigonia probably evolved from Eotrigonia (Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 to Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...

) in the Miocene.

The gills of Neotrigonia and fossil trigoniids are mineralized with calcium phosphate, which supports their chitinous scaffold support structures.

Previous research on the Trigoniidae

Because of their large size and pronounced ornament, trigoniid bivalves have long attracted interest. Jean Guillaume Bruguiere
Jean Guillaume Bruguière
Jean Guillaume Bruguière was a French physician, zoologist and diplomat.Bruguière was born in Montpellier.He was a doctor, connected to the University of Montpellier. His was interested in invertebrates, mostly snails ....

 was the first person to describe an example of Trigonia in 1789. Lamarck later figured specimens from the Oxfordian
Oxfordian stage
The Oxfordian is, in the ICS' geologic timescale, the earliest age of the Late Jurassic epoch, or the lowest stage of the Upper Jurassic series. It spans the time between 161.2 ± 4 Ma and 155.7 ± 4 Ma...

 of France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

. In England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...

 the physician
A physician is a health care provider who practices the profession of medicine, which is concerned with promoting, maintaining or restoring human health through the study, diagnosis, and treatment of disease, injury and other physical and mental impairments...

 James Parkinson
James Parkinson
James Parkinson was an English apothecary surgeon, geologist, paleontologist, and political activist. He is most famous for his 1817 work, An Essay on the Shaking Palsy in which he was the first to describe "paralysis agitans", a condition that would later be renamed Parkinson's disease by...

 (the discoverer of Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...

) described examples of Trigonia and Myophorella. Later, James Sowerby
James Sowerby
James Sowerby was an English naturalist and illustrator. Contributions to published works, such as A Specimen of the Botany of New Holland or English Botany, include his detailed and appealing plates...

 and James De Carle Sowerby
James De Carle Sowerby
James De Carle Sowerby was a British mineralogist and illustrator. He received an education in chemistry.He continued his father's work and published, together with his brother George Brettingham Sowerby I, the latter volumes of the Mineral Conchology of Great Britain, begun by their...

 began to catalogue British
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...

 examples in earnest. Etheldred Benett
Etheldred Benett
Etheldred Benett was an early English geologist, the eldest daughter of Thomas Benett of Wiltshire and Catherine née Darell ; her brother, John , was a member of Parliament for Wiltshire and later South Wiltshire from 1819 to 1852...

 added several Upper Jurassic species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...

, although her work was not primarily recognised due to the academic status of women at that time.

In Europe Louis Agassiz
Louis Agassiz
Jean Louis Rodolphe Agassiz was a Swiss paleontologist, glaciologist, geologist and a prominent innovator in the study of the Earth's natural history. He grew up in Switzerland and became a professor of natural history at University of Neuchâtel...

 published, in 1840, a large volume entitled Memoire sur les Trigonies which recognised the large variation encountered within the family, dividing it into eight sections, which was a precursor to the generic classification that occurred some fifty years later. Other notable workers that described and figured trigoniids include Friedrich August von Quenstedt
Friedrich August von Quenstedt
Friedrich August von Quenstedt , was a German geologist and palaeontologist.-Life:Von Quenstedt was born at Eisleben in Saxony, and educated at the Humboldt University of Berlin...

, Alcide d'Orbigny
Alcide d'Orbigny
Alcide Charles Victor Marie Dessalines d'Orbigny was a French naturalist who made major contributions in many areas, including zoology , palaeontology, geology, archaeology and anthropology....

 and Georg August Goldfuss
Georg August Goldfuss
Georg August Goldfuss was a German palaeontologist and zoologist.-Biography:Goldfuss was born at Thurnau near Bayreuth. He was educated at Erlangen, where he graduated Ph.D. in 1804 and became professor of zoology in 1818. He was subsequently appointed professor of zoology and mineralogy at the...


The major worker on the Trigoniidae in the nineteenth century was John Lycett, a physician from Gloucestershire
Gloucestershire is a county in South West England. The county comprises part of the Cotswold Hills, part of the flat fertile valley of the River Severn, and the entire Forest of Dean....

 who published a text entitled A Monograph of British Fossil Trigoniae.

Later research - the twentieth century

Work on the Trigoniidae has generally been sparse in the twentieth century and has mainly concentrated upon the development towards a workable taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...

. Today, knowledge is sufficient to divide the Family into five Subfamilies (see below), which together contain more than sixteen genera, the most abundant being Trigonia, Myophorella, Laevitrigonia, and Orthotrigonia.

Higher level taxonomy

  • Family Trigoniidae
    • Subfamily Trigoniinae
      • Trigonia
      • Agonisca
      • Maoritrigonia
      • Praegonia
      • Minetrigonia
      • ?Pseudomyophorella
    • Subfamily Prosogyrotrigoniinae
      • Prosogyrotrigonia
      • Prorotrigonia
    • Subfamily Psilotrogoniinae
      • Psilotrigonia
    • Subfamily Myophorellinae
      • Frenguilellella
      • Jaworskiella
      • Myophorella
        Myophorella is a genus of fossil trigoniid bivalve sometimes preserved with mineralized soft tissue....

      • Vaugonia
      • Orthotrigonia
      • Scaphotrigonia
    • Subfamily Laevitrigoniinae
      • Laevitrigonia
        Laevitrigonia is a genus of fossil trigoniid bivalve sometimes preserved with mineralized soft-tissue....

      • ?Liotrigonia

Family characteristics - trigoniid hinge

Members of the Trigoniidae are identified by the large and complex dentition
Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, the characteristic arrangement, kind, and number of teeth in a given species at a given age...

 that joins the two valves together and allows articulation
A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.-Classification:...

. The teeth and supporting area can take up almost a third of the volume of the shell. The hinge
A hinge is a type of bearing that connects two solid objects, typically allowing only a limited angle of rotation between them. Two objects connected by an ideal hinge rotate relative to each other about a fixed axis of rotation. Hinges may be made of flexible material or of moving components...

 structure is amongst the most complex of all bivalves, namely that the teeth are numerous and ridge-like with strong transverse striations. It is these striations which distinguishes the Trigoniidae from the more primitive Myophoriidae. The Trigoniidae almost certainly evolved by a monophyletic modification of a Triassic myophoriid, with three genera appearing in the Middle Triassic.

Commonly found genera

Trigoniids are commonly found in both limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....

, mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...

 and sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...

 in Jurassic and Cretaceous rocks all over the world. In Britain
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, examples are numerous in the Upper Jurassic rocks of the Dorset
Dorset , is a county in South West England on the English Channel coast. The county town is Dorchester which is situated in the south. The Hampshire towns of Bournemouth and Christchurch joined the county with the reorganisation of local government in 1974...

 coast, particularly around the village of Osmington Mills
Osmington Mills
Osmington Mills is a coastal village situated between Ringstead Bay and the town of Weymouth in Dorset, England. It is located within the civil parish of Osmington.- Tourism :...

. Other Jurassic rocks that yield specimens include the Cornbrash
In geology, Cornbrash was the name applied to the uppermost member of the Bathonian stage of the Jurassic formation in England. It is an old English agricultural name applied in Wiltshire to a variety of loose rubble or brash which, in that part of the country, forms a good soil for growing corn...

 in Yorkshire
Yorkshire is a historic county of northern England and the largest in the United Kingdom. Because of its great size in comparison to other English counties, functions have been increasingly undertaken over time by its subdivisions, which have also been subject to periodic reform...

 and the Middle Jurassic
Middle Jurassic
The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from 176-161 million years ago. In European lithostratigraphy, rocks of this Middle Jurassic age are called the Dogger....

 sequence in the Cotswolds
The Cotswolds are a range of hills in west-central England, sometimes called the Heart of England, an area across and long. The area has been designated as the Cotswold Area of Outstanding Natural Beauty...

, particularly around Cleeve Hill
Cleeve Hill
Cleeve Hill is the highest point both in the Cotswolds hill range and in the county of Gloucestershire, at . It commands a clear view to the west, over Cheltenham and the racecourse, over the River Severn and into Wales; and to the north over Winchcombe. It is a conspicuous outcrop on the edge of...

, near Cheltenham
Cheltenham , also known as Cheltenham Spa, is a large spa town and borough in Gloucestershire, on the edge of the Cotswolds in the South-West region of England. It is the home of the flagship race of British steeplechase horse racing, the Gold Cup, the main event of the Cheltenham Festival held...

. Pterotrigonia (Scabrotrigonia) thoracica has been named state fossil of Tennessee.


The genus Trigonia is the most readily identifiable member of the family, having a series of strong ribs or costae along the anterior part of the shell exterior. They are the first representatives of the family to appear in the Middle Triassic
Middle Triassic
In the geologic timescale, the Middle Triassic is the second of three epochs of the Triassic period or the middle of three series in which the Triassic system is divided. It spans the time between 245 ± 1.5 Ma and 228 ± 2 Ma...

In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from 245 million years ago until 237 million years ago, approximately...

) of Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

 and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...

. The first European examples (Trigonia costata Parkinson) turn up in the Lower Jurassic (Toarcian
The Toarcian is, in the ICS' geologic timescale, an age or stage in the Early or Lower Jurassic. It spans the time between 183.0 Ma and 175.6 Ma...

) of Sherborne
Sherborne is a market town in northwest Dorset, England. It is sited on the River Yeo, on the edge of the Blackmore Vale, east of Yeovil. The A30 road, which connects London to Penzance, runs through the town. The population of the town is 9,350 . 27.1% of the population is aged 65 or...

, Dorset and Gundershofen, Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....


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