Rudists are a group of extinct box-, tube- or ring-shaped marine heterodont bivalves belonging to the order Hippuritida that arose during the Late Jurassic and became so diverse during the Cretaceous that they were major reef-building organisms in the Tethys Ocean, until their complete extinction at the close of the Cretaceous.
Temporal range: Late Jurassic–Late Cretaceous
|Rudist bivalves from the Cretaceous of the Oman Mountains, United Arab Emirates; scale bar is 10 mm|
The Late 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 that became 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 consisted of a lower, roughly conical valve 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.
The rudists became extinct at the end of the Cretaceous, apparently as a result of the Cretaceous–Paleogene extinction event. It had been thought that this group began a decline about 2.5 million years earlier which culminated in complete extinction half a million years before the end of the Cretaceous. The extinction of rudist bivalves was stepwise during the Maastrichtian (end of the Cretaceous).
The rudists are, according to different systematic schemes, placed in the orders Hippuritida (Hippuritoida) or Rudistes (sometimes Rudista).
Bieler, Carter & Coan in 2010 also named the non-Hippuritid families Megalodontoidea and Chamoidea, of Megalodontida and Venerida respectively, as "Rudists", but this classification was not monophyletic.
The classification of rudists as true reef-builders is controversial because they would catch and trap lots of sediment between their lower conical valves; thus, rudists were not completely composed of biogenic carbonates as a coral would be. However, rudists 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 corals out of many tropical environments, including shelves that are today the Caribbean and the Mediterranean. It is likely that their success as reef builders was at least partially due to the extreme environment of the Cretaceous. During this period tropical waters were between 6°C 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. 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 American coast from the Gulf of Mexico to the present-day Maritime Provinces. Because of their high porosity, rudist reefs are highly favored oil traps.
The Angoumian is a geological group restricted to the northern Aquitaine Basin in France. The group consists of two fossiliferous limestone formations deposited during the Turonian.Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). The Mohs scale of mineral hardness, based on scratch hardness comparison, defines value 3 as "calcite".
Other polymorphs of calcium carbonate are the minerals aragonite and vaterite. Aragonite will change to calcite over timescales of days or less at temperatures exceeding 300 °C, and vaterite is even less stable.Campur Formation
The Campur Formation (Kca) is a geologic formation of the Petén Basin of northern Guatemala. The subtidal limestone preserves fossils dating back to the Late Cretaceous period.Cape Johnson Guyot
Cape Johnson Guyot is a guyot in the Pacific Ocean, more precisely in the Mid-Pacific Mountains, and the type locality of guyots. It is of middle Cretaceous age and a number of fossils have been dredged from it.Caprina
Caprina is a genus of rudists, a group of marine heterodont bivalves belonging to the family Caprinidae.These stationary intermediate-level epifaunal suspension feeders lived in the Cretaceous period, from 140.2 to 70.6 Ma. The rudists became extinct at the end of the Cretaceous, apparently as a result of the Cretaceous–Paleogene extinction event.
Fossils of this genus have been found in the sediments of Europe, Japan, Cuba, Mexico and the United States.Caprinid
Caprinid may refer to animals in the following groups:
Caprinidae, a family of extinct bivalve molluscs forming part of the Rudists
Caprinae, a family of ruminant mammals, the goat-antelopes, including sheep, goats, musk oxen and related animals more commonly known as CapridsCaprinidae
Caprinidae is a family of rudists, a group of unusual extinct saltwater clams, marine heterodont bivalves in the order Hippuritida.These stationary intermediate-level epifaunal suspension feeders lived in the Cretaceous period, from 140.2 to 66.043 Ma. The rudists became extinct at the end of the Cretaceous, apparently as a result of the Cretaceous–Paleogene extinction event.
Fossils of this genus have been found in the sediments of Europe, China, Cuba, Egypt, Guatemala, Jamaica, Japan, Mexico, Oman, the Philippines, Turkey, Russia, the United States and Venezuela.Cretaceous
The Cretaceous ( , krih-TAY-shəs) is a geologic period and system that spans from the end of the Jurassic Period 145 million years ago (mya) to the beginning of the Paleogene Period 66 mya. It is the last period of the Mesozoic Era, and the longest period of the Phanerozoic Eon. The Cretaceous Period is usually abbreviated K, for its German translation Kreide (chalk, creta in Latin).
The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas. These oceans and seas were populated with now-extinct marine reptiles, ammonites and rudists, while dinosaurs continued to dominate on land. During this time, new groups of mammals and birds, as well as flowering plants, appeared.
The Cretaceous (along with the Mesozoic) ended with the Cretaceous–Paleogene extinction event, a large mass extinction in which many groups, including non-avian dinosaurs, pterosaurs and large marine reptiles died out. The end of the Cretaceous is defined by the abrupt Cretaceous–Paleogene boundary (K–Pg boundary), a geologic signature associated with the mass extinction which lies between the Mesozoic and Cenozoic eras.Darwin Guyot
Darwin Guyot is a volcanic underwater mountain top, or guyot, in the Mid-Pacific Mountains between the Marshall Islands and Hawaii. Named after Charles Darwin, it rose above sea level more than 118 million years ago during the early Cretaceous period to become an atoll, developed rudist reefs, and then drowned, perhaps as a consequence of sea level rise. The flat top of Darwin Guyot now rests 1,266 metres (4,154 ft) below sea level.Diceratidae
Diceratidae is a family of rudists, a group of unusual extinct saltwater clams, marine heterodont bivalves in the order Hippuritida.Geology of Bonaire
The island of Bonaire began to form as part of the Lesser Antilles island arc in the past 145 million years, beginning in the Cretaceous. The island has been submerged or partially submerged for much of its existing, forming large limestone and sedimentary rock formations, atop a thick basement of volcanic rocks.Geology of Curaçao
The island of Curaçao began to form within the past 145 million years, beginning in the Cretaceous, as part of the Lesser Antilles island arc. Because the island was submerged for large parts of its history, reef environments formed atop thick layers of mafic volcanic rock, producing carbonate sedimentary rocks.Glen Rose Formation
The Glen Rose Formation is a shallow marine to shoreline geological formation from the lower Cretaceous period exposed over a large area from South Central to North Central Texas. The formation is most widely known for the dinosaur footprints and trackways found in the Dinosaur Valley State Park near the town of Glen Rose, Texas, southwest of Fort Worth and at other localities in Central Texas.Heterodonta
Heterodonta is a taxonomic subclass of saltwater clams, marine bivalve molluscs. This subclass includes the edible clams, the cockles and the Venus clams.Megalodon (bivalve)
Megalodon is an extinct genus of bivalve molluscs that reportedly lived from the Devonian to the Jurassic period. It is not clear, however, that all the fossils assigned to Megalodon from that span of time really belong in the same genus. Jurassic relatives of Megalodon such as Pachyrisma grande were closely related to the rudists.Peters Hill Limestone
The Peters Hill Limestone or Peters Hill Formation is a geologic formation in Jamaica. It preserves fossils such as rudists, echinoids and corals from the Santonian stage of the Cretaceous Period.Requienia (bivalve)
Requienia is an extinct genus of fossil saltwater clam, a marine bivalve molluscs in the order Hippuritida, family Requieniidae. These rudists lived in the Cretaceous period, from the Valanginian age (136.4–140.2) to the Campanian age (70.6–83.5 mya). They were stationary intermediate-level suspension feeders.Requieniidae
Requieniidae is a family of rudists, in the order Hippuritida, which lived from 155.7 to 66.043 million years ago.Ruwitūn̄tūn̄
Ruwitūn̄tūn̄ is a guyot in the Pacific Ocean which reaches a depth of 1,215 metres (3,986 ft) below sea level. It is capped off with a summit platform covered in sediments and some volcanic pinnacles with craters. Basaltic rocks have been found on Ruwitūn̄tūn̄.