Morphological abnormalities of orbitoidal foraminifera (Orbitoides and Omphalocyclus) from the Maastrichtian of the Zagros Mountains in northern Iraq

Many Orbitoides and Omphalocyclus individuals collected in the areas of Sura Qalat and Mokaba (northeast Sulaimani, Iraq) exhibit a number of aberrant characteristics. They contain exceptional examples of microboring activity within the tests, an uncommon test exterior form, the blossoming of equatorial chamber development, and peculiar reproductive characteristics. Orbitoid foraminiferal remains are abundant throughout the Maastrichtian stage, and the specimens from the studied areas recorded the effects of palaeoecological variables and peculiarities of their life cycles, which have important taxonomical implications. It is clear that benthic foraminifera respond to adverse ecological conditions, such as subsidence, sea level rise, and increased terrigenous input connected to the regional Laramide orogeny. Confirming this response, the overall number of individuals decreased in the upper section of the Aqra Formation. The presence of planktic foraminifera and abundant red algae indicates that the water depth has increased. The preservation of these individuals and their association with other fossils, such as Maeandropolydora osmaneliensis and Curvichnus semorbis , explain the conspicuous evidence of the activity known as microboring. The unusual exterior shapes are thought to be linked to palaeoenvironmental and sedimentological features. It is believed that the biological and genetic traits of orbitoidal taxa have a considerable impact on the formation of lateral and equatorial chambers. Additionally, multiembryo individuals and the presence of specimens with many embryos are better interpreted as a result of asexual reproduction and not a product of ecological factors on orbitoidal foraminifera that thrived in stressful settings in the Late Cretaceous.