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n. pl.1.(Paleon.) An extinct order or suborder of bivalve mollusks characteristic of the Cretaceous period; - called also Rudista. See Illust. under Hippurite.
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arcana and the extinct rudists lack the clear organic outer envelopes and uniform polygonal, cross-sectional appearance.
However, here it is obviously far more fossiliferous and displaying, for instance, abundant benthonic orbitoidal foraminiferids, red algal rhodoliths, large rudists (Dictyoptychus and Durania) and large gastropods (Campanile and Acteonella) (Figs.
Shu'aiba differs in that it contains referral build-ups of rudists surrounded by dense basinal limestones of the Bab member.
2[degrees]C) do not indicate a significant greater seasonal thermal variability when compared to seasonal studies of Cretaceous Tethyan rudists (Steuber et al.
The Upper Cretaceous sequence includes (from base to top): Semail ophiolites (serpentine andserpentinized predotite), the oldest exposed rocks in Al-Ain area, Qahlah Formation (red and yellow Unfossiliferous clast-supported conglomerates of serpentized predotite, derived from the Semail ophiolites, Simsima Formation (marine bioclastics limestones with rudists, corals and echinids, it is disconformably overlies the Qahlah Formation (Hamdan and Anan, 1993).
It also featured extinct groups such as trilobites, ammonites, rudists and archaeopteryx - the fossil that links dinosaurs to birds.
This upper interval of Unit 3 rests on a well-defined bored and oyster-encrusted hardground at the top of a 2-in-thick burrowed wackestone containing some requinid and monopleurid rudists (probably equivalent to the "Massive" marker bed of Unit 3 of Stricklin et al.
On their very edges, drilling revealed only thin constructions of abundant rudists, sponges, and some corals, implying that these organisms flourished in water depths to 30 meters below sea level; therefore, evidence is lacking for a physiographic wave resistant reef characterized by a cemented framework at sea level.
Because most rudists lived in the tropics, their die-offs give the impression that the K-T catastrophe focused there, says Raup.
Vincent and colleagues [38] believe that high levels of strontium is related to high salinity, which is in coincide to geochemical analysis carried out by Amir Bakhtiar on the rudists in Tarbur Formation.
They consist of Paleocene detrital sediments, pelagic and reef limestones with Upper Campanian -- Maastrichtian foraminiferas, rudists and corals (Azema and Tournon, 1980).