First documented record of the ammonite Turrilites costatus LAMARCK, 1801 from the Cenomanian of northern Saudi Arabia: Implications for Arabian Plate paleogeography

ABDULLAH HOMOUD ALRWAILI

This study presents the first documented occurrence of the heteromorph ammonite genus Turrilites LAMARCK, 1801, from the Cretaceous strata of the Kingdom of Saudi Arabia. A dense, in-situ fossil assemblage, dominated by numerous specimens identified as Turrilites costatus LAMARCK, 1801, was discovered in an outcrop of the Aruma Formation located 9.5 km south of the city of Ar’ar in northern Saudi Arabia. To date, the published fossil record of this genus on the Arabian Peninsula has been restricted to the Natih Formation of the Sultanate of Oman, on the southeastern margin of the Arabian Plate. The presence of Turrilites, a well-established index fossil for open-marine, outer-shelf environments, in the interior of the Arabian Plate fundamentally challenges prevailing paleogeographic models that depict this region as a shallow, restricted epeiric sea during the Cenomanian. These findings provide the first direct paleontological evidence for the existence of a persistent, open seaway connected to the Neo-Tethys Ocean that extended across the northern Arabian Plate. This discovery necessitates a significant reassessment of the region's paleogeographic maps and deepens our understanding of its complex paleoenvironmental history during a critical period of global greenhouse conditions.