Evolutionary consequences of the latest Paleocene thermal maximum for tropical planktonic Foraminifera

Author(s): Kelly, D. Clay; Bralower, Timothy J.; Zachos, James C.
Author Affiliation(s): Primary:
University of North Carolina, Department of Geology, Chapel Hill, NC, United States
University of California at Santa Cruz, United States
Volume Title: Palaeogeography, Palaeoclimatology, Palaeoecology
Source: Palaeogeography, Palaeoclimatology, Palaeoecology, 141(1-2), p.139-161. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0031-0182 CODEN: PPPYAB
Note: In English. Includes an appendix. 86 refs.; illus., incl. 2 tables, sketch map
Summary: Study of planktonic foraminiferal assemblages preserved in the central, equatorial Pacific (ODP Site 865) reveal that genera which inhabited the near-surface, mixed layer diversified during the latest Paleocene thermal maximum (LPTM). This transient diversification gave rise to a suite of short-lived (50 to several 100 ka), distinctive morphotypes (Morozovella allisonensis sp. nov., M. africana, and Acarinina sibaiyaensis) that are restricted to the LPTM interval. Parallel morphometric and stable isotopic data have been recorded from individual shells of members of the M. velascoensis/M. allisonensis and A. soldadoensis/A. sibaiyaensis lineages. The single-specimen isotope data confirm that M. allisonensis and A. sibaiyaensis are indeed stratigraphically restricted to the LPTM carbon isotope excursion; all specimens recorded anomalously low δ13C values. A stratigraphic succession of single-specimen isotope data from within the δ13C excursion interval was used to reconstruct the complex population dynamics which mediated the rapid (<10 ka) evolution of the LPTM taxa. These data reveal that local populations of ancestral M. velascoensis temporarily collapsed with the descendant M. allisonensis suddenly originating from a peripherally isolated population. This pattern is most consistent with peripatric speciation. Overall, the evolutionary transition from Acarinina soldadoensis to A. sibaiyaensis is most consistent with sympatric speciation, although certain elements of this transition are suggestive of a parapatric mechanism. We postulate that the rapid evolution of the LPTM taxa A. sibaiyaensis and M. allisonensis was fostered by a deepening of the nutrient-depleted, mixed layer. Alternatively, the LPTM morphotypes M. allisonensis and A. sibaiyaensis may have been extreme ecophenotypic variants arrayed along an intensified ecological gradient. Support for this latter interpretation is derived from the morphometric data which clearly show the morphological intergradation of the LPTM taxa with their respective ancestors. Thus, the morphologic diversification seen during the LPTM may represent failed speciations. Both scenarios invoke a temporary steepening of clinal gradients in response to intensified oligotrophy. The strong size-dependencies displayed by the δ18O and δ13C signatures of M. allisonensis and A. sibaiyaensis suggest that photosymbiosis facilitated the evolutionary success of the morozovellids and acarininids during the LPTM.
Year of Publication: 1998
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Acarinina sibaiyaensis; Allison Seamount; Biochemistry; Biodiversity; Biologic evolution; Biostratigraphy; Biotypes; C-13/C-12; Carbon; Cenozoic; Foraminifera; Geochemistry; Invertebrata; Isotope ratios; Isotopes; Leg 143; Microfossils; Mid-Pacific Mountains; Morozovella; Morozovella africana; Morozovella allisonensis; Morphology; Morphometry; North Pacific; ODP Site 865; Ocean Drilling Program; Pacific Ocean; Paleocene; Paleoclimatology; Paleoecology; Paleogene; Paleotemperature; Planktonic taxa; Protista; SEM data; Shells; Species diversity; Stable isotopes; Tertiary; Tropical environment; Upper Paleocene
Coordinates: N182624 N182626 W1793320 W1793321
Record ID: 1998043096
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands