EVOLUTION AND PALEOGEOGRAPHIC DISTRIBUTION OF THE LEPIDOCYCLINIDS

Abstract

The larger benthic foraminiferal family Lepidocyclinidae has been described extensively in the literature, with occurrences ranging from the middle Eocene in the Americas to the late Miocene (or possibly early Pliocene) in the Indo-Pacific Tethyan sub-province. Lepidocyclinids originated in the Americas but related forms are reported from West Africa from the middle Eocene-early Oligocene pointing to an eastward migration. This migration continued within the Tethys until the lepidocyclinids finally colonized the Indo-Pacific in the late early Oligocene. Various lepidocyclinid species have been used to zone and date the Neogene (particularly in the Indo-Pacific), and many, sometimes confusing, generic and suligeneric nomenclatures have been proposed to differentiate the often subtle morphological changes that have been observed to occur with time. Until now, it has not been possible to develop an effective global view of the evolution and migration of the lepidocyclinids because descriptions of specimens from the American province have been relatively rare. Here we present descriptions of new samples from 37 wells drilled off South America, and present a systematic comparison of the Lepidocyclinidae from the South America and the Tethyan sub-provinces of the Mediterranean-West Africa and the Indo-Pacific. Among the 87 specimens illustrated from the two provinces, 45 are recorded in America, including three new taxa, Lepidocyclina (Nephrolepidina) braziliana, Lepidocyclina (Nephrolepidina) americana and Eulepidina parkinsonia, and one new unnamed species of Eulepidina. By comparing the stratigraphic ranges of the South American specimens with previously described Tethyan forms, the phylogenetic evolution of the lepidocyclinids is reconstructed from their mid-Eocene origin in the Americas to their late Miocene (or possibly early Pliocene) extinction in the Indo-Pacific. Systematic comparisons enabled us to trace the timing and route of the paleogeographic migration of the lepidocyclinids from the Americas, through the Tethyan/Mediterranean corridor, and into the Indo-Pacific region. Our observations confirm that the series of global regressions in the middle Eocene and early Oligocene facilitated transoceanic migration of larger benthic foraminifera between the American and the Tethyan provinces. However, this migration stopped after rising sea-level in the early Oligocene separated the provinces. Subsequently, larger benthic foraminifera exhibited independent but similar lines of evolution. The resulting examples of parallel evolution led to some taxonomic confusion in the literature that we seek to resolve.