ANNULAR CHAMBERS IN CRETACEOUS ORBITOLINIDAE (LARGER BENTHIC FORAMINIFERA): AN OVERVIEW

Abstract

Annular chambers, if present, are usually confined to ultimate chambers within some Orbitolinidae, and were therefore regarded of subordinate importance not being included in the family diagnosis. However, this peculiar chamber type in some agglutinated conical foraminifera forms almost the entire post-embryonic part of the test. This may either be due to the general plan of test construction (e.g., in genus Coskinolinella Delmas & Deloffre, species Pseudorbitolina schroederi Luger) or represent a special test adaptation to changing environmental conditions during transgressive events (e.g., in genus Palorbitolinoides Cherchi & Schroeder). An emendation of the diagnosis of the family Orbitolinidae is here proposed to include tests that may consist completely or almost exclusively of post-embryonic annular chambers. As a result, the genus Coskinolinella Delmas & Deloffre, up to now treated as a genus of uncertain status or deleted in foraminiferal classifications, is now included in the family Orbitolinidae. Uniserial chambers with distinct concave apertural faces (appearing as stacked-cones) have erroneously been interpreted as annular chambers in the case of the late Albian-early Cenomanian Heterocoskinolina bariensis Luperto Sinni & Reina and therefore misassigned to Coskinolinella. Besides the different chamber arrangement, such an assignment would also contradict the established latest Aptian–early late Albian Coskinolinella lineage (C. daguini-C. santanderensis-C. navarrensis), and its palaeogeographically restricted occurrence.