Bradleya Problem, With Descriptions of Two New Psychrospheric Ostracode Genera, agrenocythere and Poseidonanmicus (Osreacoda: Crustacea). Smithsonian Contributions to Paleobiology, Number 12

摘要

Benson, Richard H. The Bradley a Problem, with Descriptions of Two New Psychrospheric Ostracode Genera, Agrenocythere and Poseidonamicus (Ostracoda: Crustacea). Smithsonian Contributions to Paleobiology, number 12, 138 pages, 67 figures, 14 plates, 4 table. 1972.The 'Bradleya problem' is concerned with the discovery and definition of a group of fossil and Recent reticulate ostracodes, several of which are common to Cenozoic deep-sea sediments in many parts of the world ocean floor. These species have often been misunderstood and taxonomically confused with genera characteristic of the study of shallow-water forms. The present study attempts to resolve some of these misunderstandings by designation of several important type-specimens, description of new evidence and the proposal of a new classification based on the concept of the evolution of a reticulum in response to environmental change. A method of pattern analysis is used to define elements of the reticulum subject to evolutionary change. Over 40 reticulate species, which would have at one time been regarded as Bradleya, were examined; only 14 of these are assigned and belong to Bradleya. Two new genera, Agrenocythere and Poseidonamicus, are described for the reception of the others, and these are placed in the new subfamily, Bradleyinae, and placed with Thaerocytherinae Hazel in a new family (Thaerocytheridae Hazel). Twenty-seven of these species are described, including Bradleya arata (Brady), B. dictyon (Brady), B. normani (Brady), Agrenocythere radula (Brady), A. pliocenica (Sequenza), and A. hazelae (van den Bold). The diagnostic characteristics of the related genera Cletocythereis, Oertliella, Jugosocythereis, and Hermanites are discussed and illustrated. It is concluded that the psychrospheric species Agrenocythere pliocenica, which has been reported from outcrops in Italy and a long core from the Tyrrhenian Sea floor, is most closely related to A. hazelae, which became geographically widespread during the Miocene. Bradleya, Jugosocythereis, Agrenocythere, and Cletocythereis, now genera in separate families, are all thought to have been derived from a common stock of Cretaceous age.