The Oligocene nannolith Sphenolithus evolutionary lineage : morphometrical insights from the palaeo-equatorial Pacific Ocean

• Changes in morphology within the biostratigraphically important Oligocene nannofossil lineage, Sphenolithus predistentus-distentus-ciperoensis, were investigated in carbonate sediments from the paleo-equatorial Pacific Ocean Site 1218 in order to determine the nature of this evolutionary lineage. Using differences in their morphology and stratigraphic ranges, the aim of this study was to determine whether this set of sphenolith species represents an anagenetic evolutionary lineage or a set of discrete species with overlapping geological ranges. 1000 specimens were analysed morphometrically and the basal ratio (the ratio between the proximal cycle height and basal width), was identified as a key parameter for study of this lineage. We conclude that S. distentus and S. predistentus are intergradational species forming an anagenetic lineage but that S. ciperoensis is a discrete species which evolved relatively abruptly in the Late Oligocene.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

Nyckelord

Oligocene

Sphenolithus predistentus

S. distentus

S. ciperoensis

evolutionary lineage

morphometry

ODP Leg 199 Site 1218

Pacific Ocean

Historical geology and palaeontology

Historisk geologi och paleontologi

Geology

geologi

Earth Science with specialization in Historical Geology and Palaeontology

Publikations- och innehållstyp

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