The middle to upper Eocene mixed carbonate-clastic and siliciclastic deposits of the Şevketiye and Keşan formations in northwest Turkey yielded unique assemblages of larger benthic foraminifera, some displaying a typical orbitoidiform test, not comparable to any known taxa in the Palaeogene of the Neo-Tethys. These specimens with a flat, discoidal test, occasionally with an indistinct central depression, possess a central layer of equatorial chambers/chamberlets displaying a cyclical (orbitoidal) growth pattern and thick lateral layers with numerous chamberlets. The megalospheric embryonic apparatus possesses three small chambers (a triconch, the chambers of which are separated by notably thin walls), followed by a large auxiliary chamberlet. These specimens closely correspond to the genus Caudriella Haman and Huddleston and its type-species Margaritella ospinae (Caudri) that has only previously been reported with confidence from the Caribbean region, notably the type locality within the middle Eocene Punta Mosquito Formation at Margarita Island off Venezuela. Caudriella at its type locality also possesses a trilocular embryonic apparatus, which was incorrectly interpreted as arranged in a rectilinear or slightly curved row. The diagnosis of Caudriella is emended and considering the similarities in their equatorial sections with closely associated Linderina Schlumberger, a comparison of their embryonic-nepionic stages is given from the same deposits in NW Turkey and with those from the middle Eocene of the Sulaiman Range (Pakistan) and Kutch (India). A new record of primitive Caudriella is presented from Jamaica. The palaeobiogeographic distribution of Caudriella is reconsidered, being recorded from both the American/Caribbean and the Western Neo-Tethys bioprovinces. Limited data suggest eastward directed dispersal of the genus, even though this would be counter to most of the prevailing surface currents during the Eocene.
Orthophragmines are a group of discoidal, lenticular or stellate ‘orbitoidal’ larger benthic foraminifera that thrived in shallow-marine environments in low-to-middle latitudes during the late Paleocene and Eocene. They consist of two phylogenetically independent families with similar morphology, such as Discocyclinidae (with two Tethyan genera—Discocyclina and Nemkovella) and Orbitoclypeidae (with three genera—Orbitoclypeus, Asterocyclina and Hexagonocyclina in the Tethys) distinguishable by the different microspheric juvenarium of the microspheric (B) forms. Sixty-one species of orthophragmines are herein described and illustrated based on material from various Tethyan localities in Europe, North Africa, Turkey, the Arabian Peninsula, the Indian Subcontinent and SE Asia. Thirty-two species of Discocyclina, six species of Nemkovella, thirteen species of Orbitoclypeus, nine species of Asterocyclina and one species of Hexagonocyclina are included. Some species include chrono-subspecies, established by applying the principles of embryonic and nepionic acceleration in the megalospheric (A) forms, primarily expressed by the increase in the size of the deuteroconch, morphological modifications forming various embryonic configurations through the phylogeny, and the increase in the number of adauxiliary chamberlets that arise from the embryonic apparatus. This study is mainly based on investigating oriented sections of many free specimens, and some random rock thin sections where obtaining free tests of orthophragmines was not possible. The Atlas is designed as a laboratory handbook for micropaleontology students and a guidebook to assist professionals with the easy identification of orthophragmines in thin sections.
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