|Fluctuations in ammonoid evolution and possible environmental controls|
House, M.R. (1993). Fluctuations in ammonoid evolution and possible environmental controls, in: House, M.R. (Ed.) The Ammonoidea: environment, ecology, and evolutionary change. pp. 13-34
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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VLIZ: Geology and Geophysics 
Fluctuations in the evolution and occurrence through time of ammonoids, or of any organism, give an indication of changes in the conditions relating to their growth or their preservation. This bioseismograph provides our best record for elucidating the cause of past environmental change. At the smallest scale, ammonoid occurrences are linked to sedimentary microcycles which are pervasive throughout many ammonoid-bearing rocks. Small-scale analysis of evolution will always be hampered by these punctuations, some of which are certainly due to Milankovitch Band climatic forcing, and these give promise of quite new time-scales for geology with units in the band 10-500 Ka: of course many sedimentary micro cycles have quite different causes. Nevertheless, at the finest resolution, these effects are often well documented by the ammonoid record. At a rather larger scale are extinction and diversification events. There are about eight of these which are important in the Devonian: these have not been shown to be periodic, but they occur in a 1-5 Ma frequency band. They are often associated with dysaerobic events and show a gradual deterioration, event acme with many extinctions, and a progressive subsequent build-up of novelty. Such events in the late Givetian, end Frasnian and end Famennian almost saw the complete demise of the Ammonoidea. At the largest scale, ammonoid evolution shows major extinction phases, which seem correlatable with sea-level changes, especially at the end Permian, end Triassic and end Cretaceous. An analysis at this scale has been undertaken using family-level extinctions from the early Devonian to end Cretaceous at 2 Ma units. This shows a good correlation with documented sea-level modifications for the Mesozoic. Fourier transforms show no evidence for a periodicity in the order of 26 Ma. A causal relation with major global changes driven by plate tectonics is preferred.