A revision of (early) Burdigalian hyaline larger foraminifera based on the biometric study of miogypsinids, lepidocyclinids, and nummulitids from eastern Turkey provides new insights into their taxonomy and paleo-biogeography in the Tethys region. Data from the Adilcevaz Formation show a strong similarity to occurrences from Southeast Asia in that they include Cycloclypeus, Eulepidina, and “ribbed” Nephrolepidina, an assemblage not previously recorded from age-equivalent deposits in the circum-Mediterranean region. The association and the occurrences of these taxa in Lower Miocene deposits from the Indo–West Pacific areas have been widely reported. The species designation of Nephrolepidina and Eulepidina, in the absence of well-demonstrated comparable biometric and conflicting stratigraphic data from the Indo–West Pacific areas, is usually problematic. The Turkish taxa bear a close resemblance to N. sumatrensis and E. formosa, whilst Cycloclypeus is represented by C. eidae, which is widespread in the Indo-Pacific Early Miocene. These taxa are accompanied by Miolepidocyclina burdigalensis, a well-documented side branch of the main Miogypsina lineage in the circum-Mediterranean region; Miogypsina globulina, a worldwide tropical species common to both provinces; and Operculina complanata. Our data provide the first foraminiferal evidence from Turkey suggesting a main westward migration of several important groups from Southeast Asia to the eastern Mediterranean during the (early) Burdigalian. This faunal incursion is the most significant compared to other Late Oligocene–Early Miocene foraminiferal events in Turkey.

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