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Origin of the Eocene planktonic foraminifer H antkenina by gradual evolution
Author(s) -
Pearson Paul N.,
Coxall Helen K.
Publication year - 2014
Publication title -
palaeontology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.69
H-Index - 63
eISSN - 1475-4983
pISSN - 0031-0239
DOI - 10.1111/pala.12064
Subject(s) - foraminifera , paleontology , plankton , biostratigraphy , biology , genus , taxonomy (biology) , convergent evolution , habitat , geology , ecology , evolutionary biology , phylogenetics , benthic zone , gene , biochemistry
H antkenina is a distinctive planktonic foraminiferal genus characterized by the presence of tubulospines (robust hollow projections) on each adult chamber, from Middle and Upper Eocene marine sediments worldwide. Here we illustrate its evolutionary origin using c . 150 specimens from 30 stratigraphic intervals in two sediment cores from T anzania. The specimens, which span an estimated time interval of 300 ka, show four intermediate steps in the evolution of the tubulospines that amount to a complete intergradation from C lavigerinella caucasica , which does not possess them, to H antkenina mexicana , which does. Stable isotope analyses indicate that the transitional forms evolved in a deep planktonic habitat not occupied at that time by other species of planktonic foraminifera. We discuss the morphogenetic constraints involved in the evolutionary transition and propose an ecological/adaptive model for the selective pressures that resulted in the evolution of tubulospines. We compare our record with similar, recently described assemblages from A ustria and Italy, and we update the biostratigraphy and systematic taxonomy of the key morphospecies involved in the transition.