Size variations of coccoliths in Cretaceous oceans : a result of preservation, genetics and ecology?
Articolo
Data di Pubblicazione:
2015
Citazione:
Size variations of coccoliths in Cretaceous oceans : a result of preservation, genetics and ecology? / N. Luebke, J. Mutterlose, C. Bottini. - In: MARINE MICROPALEONTOLOGY. - ISSN 0377-8398. - 117(2015 May), pp. 25-39. [10.1016/j.marmicro.2015.03.002]
Abstract:
Biometric studies of coccoliths, the remains of coccolithophores, offer the opportunity to survey
single species instead of entire assemblages. We obtained and analyzed size data of three
common species (Biscutum constans, Zeugrhabdotus erectus and Watznaueria barnesiae) in a
stratigraphically very well-defined interval of early Aptian age (~126 Ma; Cretaceous). Material is
derived from four sites (Lower Saxony Basin, North Sea, western Tethys, Mid-Pacific) covering
nearshore to open-oceanic paleosettings.
Length and width measurements of 1986 specimens were evaluated. The recorded size
patterns show a larger data spread for B. constans and W. barnesiae in the western Tethys and
the Mid-Pacific than in the North Sea and the Lower Saxony Basin. The latter two sites are
dominated by small coccoliths of B. constans while coccoliths of W. barnesiae show similar sizes
at all four sites. Solely small specimens of Z. erectus characterize the samples from the North Sea
and the Lower Saxony Basin while only large ones are present in the samples of the western
Tethys and Mid-Pacific.
For explaining the recorded size patterns, three theories are discussed in detail; these include
(1) preservation of nannofossils, (2) genetics and (3) palecology. (1) Intense dissolution or
overgrowth of the nannofossils may have altered the original coccolith sizes particularly when
biometric data from different sites with potentially varying states of preservation are compared.Due to its delicate morphology, Z. erectus appears most prone to dissolution, probably explaining
its size pattern. (2) If the recorded size data of the remaining two species represent original
patterns, these can be interpreted by new findings in recent coccolithophore genetics. It has been
shown that size variations within a single cryptic species are only minor. Shifts of coccolith sizes,
both in recent and fossil taxa, can be related to genotypic variation. The varying size ranges
recorded for B. constans and W. barnesiae may therefore reflect diversity changes of cryptic
species at the different sites. (3) These cryptic species may have preferred different depth habitats
depending on geographically-controlled factors such as sea-surface temperatures, light availability
or trophic load.
Tipologia IRIS:
01 - Articolo su periodico
Keywords:
Biometry; Calcareous nannofossils; Cretaceous; Preservation; Sea-surface temperature; Light availability
Elenco autori:
N. Luebke, J. Mutterlose, C. Bottini
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