Tusoteuthis is an extinct genus of large enchoteuthine cephalopod that lived during the Cretaceous. Although often called a squid, it is now thought to be more closely related to modern octopuses. Although many specimens from Western Interior Seaway of North America were described, at 2019, only one, poorly preserved specimen from Kansas is recognized as Tusoteuthis. One species, T. longa, is traditionally recognized. In 2019, due to poor preservation of holotype specimen, Tusoteuthis was considered likely to be a nomen dubium, and it was proposed that later described species are better to included in genus Enchoteuthis instead.^[2]

American paleontologist William N. Logan did not directly explain the etymology of Tusoteuthis when he named it in 1898.^[3] The generic name may be formed from Latin tusus "crushed" (passive participle of Latin tundo "beat, crush") + Greek teuthis "squid", alluding to the typically fragmented condition of the fossil gladius.^[4] The gender of the type species name was later corrected to the Latin feminine longa.

Due to fragmentary nature of holotype specimen, it is hard to determine other specimens that are described as T. longa are actually belonging to that species, and species T. longa itself is likely to be nomen dubium. Some of specimens, including gladius remains which has yielded an estimated mantle length close to or equal to that of the modern giant squid, should be classified as specimens of Enchoteuthis melaneae instead. Another species of Tusoteuthis, T. cobbani was also reclassified to genus Enchoteuthis.^[2]

Enchoteuthids like Tusoteuthis are estimated to be active predators.^[2] Fossils that are described as Tusoteuthis were found to be preyed on by other animals, especially the many, various predatory fish of the Western Interior Seaway. A fossil of the predatory aulopiform, Cimolichthys nepaholica, was found with the gladius of T. longa in its gullet. The back portion of the gladius was in the stomach region, while the mouth of C. nepaholica had remained opened, suggesting that the fish had died in the middle of swallowing the cephalopod, tail first. Researchers strongly suspect that as the fish was swallowing Tusoteuthis, the head and/or tentacles remained outside the mouth, thus blocking the gills of the fish, and suffocating it as it swallowed its prey.^[5]

• Cephalopod size
• Enchoteuthis