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Rudists are a group of bizarrely shaped marine
Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology....
 heterodont
Heterodont

The anatomical term heterodont refers to animals which possess more than a single tooth morphology . For example, members of the Synapsida generally possess incisors, Canine_, premolars, and molars....
 bivalves that arose during the Jurassic
Jurassic

The Jurassic is a geologic period that extends from about annum to  Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
, and became so diverse during the Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 that they were major reef-building organisms in the Tethys Ocean
Tethys Ocean

The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean....
.

Jurassic forms were elongate, with both valves being similarly shaped, often pipe or stake-shaped, while the reef-building forms of the Cretaceous had one valve become a flat lid, with the other valve becoming an inverted spike-like cone.






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Rudists are a group of bizarrely shaped marine
Marine (ocean)

Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology....
 heterodont
Heterodont

The anatomical term heterodont refers to animals which possess more than a single tooth morphology . For example, members of the Synapsida generally possess incisors, Canine_, premolars, and molars....
 bivalves that arose during the Jurassic
Jurassic

The Jurassic is a geologic period that extends from about annum to  Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
, and became so diverse during the Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
 that they were major reef-building organisms in the Tethys Ocean
Tethys Ocean

The Tethys Ocean was an ocean that existed between the continents of Gondwana and Laurasia during the Mesozoic era before the opening of the Indian Ocean....
.

Shell description

The Jurassic forms were elongate, with both valves being similarly shaped, often pipe or stake-shaped, while the reef-building forms of the Cretaceous had one valve become a flat lid, with the other valve becoming an inverted spike-like cone. The size of these conical forms ranged widely from just a few centimeters to well over a meter in length.

Their "classic" morphology
Morphology (biology)

The term morphology in biology refers to form, structure and configuration of an organism. This includes aspects of the outward appearance as well as the form and structure of the internal parts like bones and organs....
 consisted of a lower, roughly conical valve
Valve

A valve is a device that regulates the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe Piping and plumbing fittings, but are usually discussed as a separate category....
 that was attached to the seafloor or to neighboring rudists, and a smaller upper valve that served as a kind of lid for the organism. The small upper valve could take a variety of interesting forms, including: a simple flat lid, a low cone, a spiral, and even a star-shaped form (Johnson, 2002).

Fossil range and extinction

The rudists went extinct at the end of the Cretaceous, apparently as a result of the Cretaceous–Tertiary extinction event. It had been thought that this group began a decline about 2.5 million years earlier which culminated in their complete extinction half a million years before the end of the Cretaceous (Johnson, 2002). However, evidence now suggests that rudists did actually survive up until the mass extinction event, and perished in that event (Steuber et al. 2002).

Taxonomy

The rudists are, according to different systematic schemes, placed in the order
Order (biology)

In Biological classification used in biology, the order is a taxonomic rank between class and family . The superorder is a rank between class and order....
s Hippuritoida or Rudistes (sometimes Rudista).

Ecology

Their classification as true reef-builders is controversial because they would catch and trap lots of sediment between their lower conical valves, meaning that they are not completely composed of biogenic carbonates as a coral reef
Coral reef

Coral reefs are aragonite structures produced by living organisms. In most reefs the predominant organisms are colonial cnidarian that secrete an exoskeleton of calcium carbonate....
 would be. However they were one of the most important constituents of reefs during the Cretaceous Period. During the Cretaceous, rudist reefs were so successful that they drove scleractinian
Scleractinia

Scleractinia, also called Stony corals, are exclusively marine animals; they are very similar to sea anemones but generate a hard skeleton....
 corals out of many tropical environments, including shelves that are today the Caribbean
Caribbean

The Caribbean is a region consisting of the Caribbean Sea, its islands , and the surrounding coasts. The region is located southeast of the Gulf of Mexico and Northern America, east of Central America, and to the north of South America....
 and the Mediterranean. It is likely that their success as reef builders is at least partially due to extreme environment of the Cretaceous. During this period tropical waters were between 6 and 14 C° warmer than today and also more highly saline, and while this may have been a suitable environment for the rudists, it was not nearly so hospitable to corals and other contemporary reef builders (Johnson, 2002). These rudist reefs were sometimes hundreds of meters tall and often ran for hundreds of kilometers on continental shelves, in fact at one point they fringed the North America
North America

North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere....
n coast from the Gulf of Mexico
Gulf of Mexico

The Gulf of Mexico is the ninth largest body of water in the world. Considered a smaller part of the Atlantic Ocean, it is an oceanic basin largely surrounded by the North American continent and the island of Cuba....
 to the present-day Maritime Province
Maritimes

The Maritime provinces, also called the Maritimes or the Canadian Maritimes, is a list of regions of Canada#National regions of Eastern Canada consisting of three provinces and territories of Canada: New Brunswick, Nova Scotia, and Prince Edward Island....
s. Because of their high porosity
Porosity

Porosity is a measure of the void spaces in a material, and is measured as a fraction, between 0?1, or as a percentage between 0?100%. The term is used in multiple fields including ceramics, metallurgy, materials, manufacturing, earth sciences and construction....
, rudist reefs are highly-favored oil traps.

See also

  • Inoceramus
    Inoceramus

    Inoceramus is an extinct genus of fossil Marine pteriomorphian bivalves that superficially resembled the related winged pearly oysters of the extant genus Pteria....