Single-specimen stable isotope analyses to investigate evolutionary changes in coiling ratios and depth ecology within the middle Miocene Globorotalia (Fohsella) lineage

Author(s): Eisenach, Adam R.; Kelly, D. C.
Author Affiliation(s): Primary:
University of Wisconsin at Madison, Geology and Geophysics, Madison, WI, United States
Volume Title: Geological Society of America, 2003 annual meeting
Source: Abstracts with Programs - Geological Society of America, 35(6), p.161; Geological Society of America, 2003 annual meeting, Seattle, WA, Nov. 2-5, 2003. Publisher: Geological Society of America (GSA), Boulder, CO, United States. ISSN: 0016-7592 CODEN: GAAPBC
Note: In English
Summary: Historically, the Globorotalia (Fohsella) lineage has been considered a flagship for phyletic gradualism within the planktonic foraminifera. This lineage displays gradual morphological evolution during the early-to-middle Miocene transition from G. (Fohsella) peripheroronda to G. (Fohsella) fohsi. This prolonged period (∼10 m.y.) of gradual morphological evolution is, however, punctuated by an abrupt (∼50 k.y.) deepening in habitat depth that is roughly coincident with the FAD of G. (Fohsella) fohsi at ∼12.9 Ma. Examination of G. (Fohsella) assemblages preserved through this same stratigraphic interval at ODP Site 806 reveals that this well-documented ecological shift is paralleled by a significant change in the lineage's preferred direction of coiling. Specifically, coiling ratios within the plexus exhibit a modest tendency to be dextrally coiled prior to 12.9 Ma (∼35% sinistrally-coiled), but switch to predominantly sinistral coiling (∼97%) through the stratigraphic interval in which the depth-habitat shift is recorded. Moreover, the fohsellids suffered a transient decline in overall relative abundance during this critical stage of their ecological evolution, a possible indication that environmental change temporarily perturbed local population structures and paleobiogeography. The temporal relationship between the abrupt changes in coiling preference and ecological evolution within the G. (Fohsella) lineage has been previously overlooked. Single-specimen stable isotope (δ18O, δ13C) analyses were employed to determine if subtle, depth-habitat differences could be detected between sinistrally and dextrally coiled individuals prior to the concurrent shifts seen in depth-habitat and preferred direction of coiling. The preliminary data suggests that no significant difference in preferred depth ecology existed between sinistrally and dextrally coiled individuals prior to the depth-habitat shift; it appears that both dextrally- and sinistrally-coiled subpopulations calcified their shells within the warm, mixed layer. Future study will provide additional stable isotope data which are needed to clarify the depth-habitat preferences of these fohsellid subpopulations and to refine our interpretations.
Year of Publication: 2003
Research Program: ODP Ocean Drilling Program
Key Words: 10 Paleontology, Invertebrate; Biologic evolution; C-13/C-12; Carbon; Cenozoic; Chemical composition; Coiling; Faunal studies; Foraminifera; Geochemistry; Globigerinacea; Globorotalia; Globorotaliidae; Habitat; Invertebrata; Isotope ratios; Isotopes; Leg 130; Microfossils; Miocene; Morphology; Neogene; O-18/O-16; ODP Site 806; Ocean Drilling Program; Oxygen; Paleoecology; Planktonic taxa; Protista; Rotaliina; Stable isotopes; Tertiary
Coordinates: N001906 N001907 E1592142 E1592140
Record ID: 2004083052
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States