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Phyletic evolution of desmoceratine ammonoids through the Cenomanian-Turonian oceanic anoxic event
Hirano, H. (1993). Phyletic evolution of desmoceratine ammonoids through the Cenomanian-Turonian oceanic anoxic event, in: House, M.R. (Ed.) The Ammonoidea: environment, ecology, and evolutionary change. pp. 267-283
In: House, M.R. (Ed.) (1993). The Ammonoidea: Environment, ecology, and evolutionary change. The Systematics Association Special Volume, 47. Clarendon Press: Oxford. ISBN 0-19-857765-6. 353 pp., more
In: The Systematics Association Special Volume, more
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  • Hirano, H.
Abstract
    Samples were obtained from the anoxic and oxic beds in and around the Cenomanian-Turonian (C/T) boundary of Tunisia and south-east France, and sulphur content was confirmed as a reliable index of anoxic conditions. Using this, the anoxic conditions of the black shale in the Cenomanian - Turonian boundary were confirmed for the Yezo Supergroup, Hokkaido, Japan which was a sequence deposited in the outer shelf to the upper shelf-slope basin of a fore-arc basin. The phyletic speciation from the Cenomanian Desmoceras (Pseudouhligella) japonicum to Turonian Tragodesmoceroides subcostatus arose at the C/T boundary in the northwestern Pacific. It is reasonably explained in relation to the oceanic anoxic conditons that most D. (P.) japonicum populations died out at the end of the Cenomanian and T. subcostatus phyletically arose from a small population of the former which had successfully taken refuge in shallower waters. The distribution of the descendant species was limited to shallower waters than the ancestral species.
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