Rudists

Rudist chalk, UAE

  • Worldwide

The rudists ( Hippuritoida ) are an extinct order of mussels ( Bivalvia ), which are provided subclass Heterodonta within this class. Rudists are characterized by strong ungleichklappige and usually completely aberrant case. They first appear in the Upper Jurassic and die out at the Cretaceous - Tertiary boundary.

Characterization

The housing of the typical rudists are inequivalve and attached with a half case to the substrate or they lie on the sediment. The housings are bell-shaped with a lid or spirally wound with a smaller " top flap ". The shells are usually and often traversed extremely thick with longitudinal channels and cavities. The outer shell layer is composed of the mineral calcite, while the inner layer is aragonitisch. Through the good preservation potential of calcite ( compared with aragonite, which is much more soluble ), the rudists a very good fossil record. The castle, originally heterodont, is considerably remodeled ( pachydont ), and has only one or two main teeth. The ligament is also changed significantly.

Way of life

Due to their sessile lifestyle in warm shallow water, it is assumed that they, like today's giant clams, living in symbiosis with photosynthetic bacteria or algae operated.

System

The order Hippuritoida ( rudists ) contains only the superfamily

  • Hippuritoidea Gray, 1848 ( "real" rudists ). The rudists are attached, with the exception of the last family, each with the right door to the substrate. Diceratidae Dall, 1895
  • Hippuritidae Gray, 1848
  • Monopleuridae Munier - Chalmas, 1873
  • Radiolitidae Gray, 1848
  • Caprinidae d' Orbigny, 1850
  • Polyconitidae Mac Gillavry, 1937
  • Plagioptychidae Douville, 1888
  • Ichthyosarcolitidae Douville, 1887
  • Antillocaprinidae Mac Gillavry 1937
  • Dictyoptychidae Skelton Skelton & Benton, 1993
  • Caprotinidae Gtay, 1848
  • Requieniidae Douville, 1919 ( this family is attached to the left door to the substrate ).

Some authors will also add the superfamily Megalodontoidea Morris & Lycett, 1853 made ​​to order.

Mya (unit) Norman D. Newell
392967
de