megagrumbulla

Megagrumbulla is a recognized genus of extinct cephalopods that lived during the early Middle Jurassic period. The taxon falls within the family Grumbullidae, a group of nautiloid-like cephalopods characterized by long, straight sutures and a pronounced shell ornamentation. Fossils attributed to Megagrumbulla have been recovered primarily from the Marmara Basin in southeastern Turkey, though isolated remains have been reported from the Bohemian Basin in Czech Republic. The genus is known from a limited number of well-preserved specimens, most of which represent juvenile and subadult individuals.

Morphologically, Megagrumbulla species are distinguished by a robust, cylindrical shell measuring approximately 20–35 centimetres in length, with subtle concentric ridges along the dorsal side and a well-developed siphuncle positioned slightly ventrally. The aperture is relatively narrow and the phragmocone contains several well-developed chambered sections. Comparative analysis with contemporaneous cephalopods such as Grumbullus and Phylloceras indicates a distinct lineage that may have had a benthic rather than free-swimming lifestyle. The shell composition is dominated by aragonitic lamellae, a feature common among middle Jurassic cephalopods.

The name Megagrumbulla derives from the Greek root "mega," meaning large, and the genus name Grumbullus, reflecting its larger size and close relationship to the type genus of its family. The initial description was published in 1914 by paleontologist Adolf Hedberg, based on a holotype designated by the specimen number TM-1942. Subsequent revisions in the 1970s and 1990s reaffirmed its taxonomic status while refining its morphological character set. Despite its sparse fossil record, Megagrumbulla contributes to a broader understanding of cephalopod diversity during the Middle Jurassic and offers insight into the evolutionary pathways that led to modern nautiloids.