Nr 408 Evaluation of Pliocene Scyphosphaera ( Lohmann 1902 ) Taxonomy at IODP Sites U 1462 and U 1463 , Northwestern Australia

Evaluation of Pliocene Scyphosphaera (Lohmann 1902) Taxonomy at IODP Sites U1462 and U1463, Northwestern Australia Nina Caf The coccolithophore genus Scyphosphaera exhibits two distinct types of coccoliths: muroliths that are spherical in shape and lopadoliths that are vase or cup-shaped. Extant species show highly polymorphic lopadoliths that can vary in size and shape on one single cell. In the past, especially in the Pliocene, the genus Scyphosphaera was morphologically highly diverse, which makes it a great group for studying evolutionary and ecological processes. The main aim of this study was to quantitatively analyze the morphological variation of lopadoliths found in two drill sites, Site U1462 and Site U1463, on the northwestern continental margin of Australia as part of the International Ocean Discovery Program (IODP). These sites were drilled during IODP Expedition 356 that documented sedimentary sequences of the last 5 million years, during which the Earth experienced major changes in climate moving from warmer to ice age conditions (Gallagher et al. 2017). The second aim was to recognize whether the morhological variation represents phenotypic variation within one or few (morpho) species of Scyphosphaera or if those differences in morphology are indicative of distinct species. A third aim was to compare regional and lateral diversity and abundance of the Scyphosphaera genus in the samples from both sites for understanding regional changes in the (postdepositional) environment. Three different groups were determined, depending on the shape and based on 1, 4 or 5 measured parameters of the lopadoliths. In group I, five parameters were defined, in group II, four parameters were defined and in group III only one parameter was defined. In order to determine the absolute abundance of Scyphosphaera species within the sediment, the drop technique (Bordiga, Bartol & Henderiks 2015) was used for preparation of microscope slides. A linear age model was constructed using three marker taxa. Altogether 440 specimens were collected and included in the biometric analysis. The biometric analysis showed that morphotypes 1 and 6 included in group I are different in shape and size, which makes them an interspecific variation of two separate species. In group II, morphotype 7 differs from all other morhotypes and is therefore regarded as separate morphospecies, which was further proven by t-tests that showed significant differences between most size parameters. Other morphotypes in group II were considered to be a part of a single morphospecies. The morphotype in group III was interpreted to be a »top view« and a cross section of lopadoliths that were filled with minerals during diagenetic processes. Comparison of abundance of morphotypes at Site U1462 and Site U1463 demonstrated higher abundance at Site U1463. Diagenetic alterations are probably the reason for lower abundance at Site U1462. Both sites were interpreted as a coastal hemipelagic environment, which is consistent with the setting in which the genus Scyphosphaera thrives. Biometric analysis clearly shows that, with this method of distingushing between morphotypes, more can be said about the number of morphospecies that are found in the fossil record. Altogether, from 10 morphotypes only four morphospecies have been recognized, which indicates lower number of taxa in the early Pliocene.