Jurassic/Cretaceous Epistominidae from Canada and Europe

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Abstract
Mesozoic sediments from the continental margin off eastern Canada and the Lusitanian Basin of Portugual yield rich and diversified assemblages of the benthic foraminifer Epistomina. Close examination, documentation and illustration of the distinctive morphologies of different species of this genus together with comparisons with holotypic and other material from the North Atlantic and Europe has enabled the recognition of three distinct morphotypes. The first group is made up of morphologically conservative smooth forms which are geologically long ranging. A second group is distinctively ornamented with a central umbilical collar or reticulae and possesses a weakly to strongly developed secondary keel. The third group has a first order ornamentation of pitting and lacks the central umbilical collar or reticulae. An extensive review of pertinent literature, particularly Russian sources, facilitates the understanding of the geological history of each morphotype and serves also to highlight the surplus of names that are used for what appears to be relatively few species. The evolution of the epistominid group is broadly characterized by periods of diversification of morphotypes punctuated by times of "crisis" where only smooth types persist. Only the smooth morphotype has an Early Jurassic to Recent history. All species of the other morphotypes become extinct in the Cretaceous. Reduction of morphotypes (the latter involving the virtual disappearance of all ornamented forms) during the Late Jurassic and again in the late Albian is coincident with the widespread development of carbonate type sedimentation patterns in the Atlantic and mediterranean Tethys margins suggesting a broad relationship between epistominid predominance and the availability of suitable clay/shale type facies. The impact of this relationship on observed patterns of evolution within the epistominid group and the impetus behind their evolution is discussed.