Phylogeny of Deep-Sea Calcareous Trochospiral Benthic Foraminifera: Evolution and Diversification

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Abstract
The phylogeny, evolutionary trends, and timing of diversification of deep-sea organisms remain largely unknown. The purpose of this paper is to highlight the taxonomy and phylogeny of deep-sea calcareous trochospiral benthic foraminiferal genera which mainly inhabit the top few centimeters of sea floor sediment. This report describes the phylogeny of 19 genera including five new genera and 17 new species, and a new taxonomic classification at the family level. The classification of families and the phylogeny of genera based on morphological intergradation differs fundamentally from previous taxonomic schemes which used radial-granular texture as one of the important categories for suprageneric classification. Two types of generic evolution are recognized: (a) evolution starting from small species (>400 mu m) and occurring during Aptian and Turonian to Santonian time and (b) that starting from lar er species occurring during the Campanian to Paleocene. Low dissolved oxygen conditions may have caused the former type of evolution and high dissolved oxygen states may have led to the latter. General evolutionary trends among the trochospiral group include a decrease in roundness of the peripheral margin, development of a peripheral keel, a distinct increase in pole size, and an increase in test size. The phylogeny exhibits major diversifications in the early Aptian to early Albian(118-110 Ma) and Turonian to early Maastrichtian(91-71 Ma), subsequent to two major mid-Cretaceous anoxic events. No distinct diversification of calcareous trochospiral genera occurred during the latest Cretaceous to Holocene. The timing of major diversifications among deep-sea foraminiferal faunas differs from early Cenozoic diversifications experienced by terrestrial and pelagic faunas. This suggests that different paleoenvironmental causes affected the evolution of deep-sea foraminifera and surface dwelling faunas (mammalia and planktonic foraminifera), over the past 120 m.y.