Definition of rudist in US English:


(also rudistid)


  • A cone-shaped extinct bivalve mollusk that formed colonies resembling reefs in the Cretaceous period.

    Superfamily Rudistacea, order Hippuritoida

    • ‘Most of the characteristic life forms of the Cretaceous had not yet evolved or were insignificant, including angiosperms, mosasaurs, therian mammals, hadrosaurs, rudists, calcareous plankton and planktonic foraminifera.’
    • ‘An extinct group of Mesozoic bivalves, the rudistids, became closely adapted to a cemented mode of life: one valve became conical while the other formed a lid.’
    • ‘Aptian reefs were typically composed of rudists.’
    • ‘This member contains abundant and diverse mid-Cretaceous shallow-marine invertebrates, including reef corals and rudist bivalves.’
    • ‘The limestone clasts contain rudist fragments and larger foraminifera that indicate erosion from the Campur Formation.’
    • ‘These two species are not as yet known to be associated with rudists or corals, although a few specimens of both rudists and corals have been recovered from other localities of Turonian age in the Santa Ana Mountains.’
    • ‘Most of the rudist species listed by these authors are typical late Albian taxa, but their purported occurrences here require additional study and supportive documentation.’
    • ‘The seas were inhabited by large ammonoids like Olcostephanus, bivalves like Bruchia, and (in selected areas) some of the early rudist reefs.’
    • ‘Cretaceous radiations of rudists were apparently initiated during periods of globally high sea level and the Lebanon decapod faunas are a part of this general increasing invertebrate diversity.’
    • ‘Data from the Pacific Ocean on the distribution of rudists on carbonate platforms confirm that biocalcification crises in shallow-water settings were truly global.’
    • ‘Many rudist species were defined on specimens collected from the El Abra Formation in Mexico, a widespread carbonate platform.’


Late 19th century: from modern Latin Rudista (former group name), from Latin rudis ‘rude’; for the variant spelling see -id.