Tusoteuthis was a giant squid nearly equal in size to those that ply the oceans today—with their tentacles stretched out, the ancient cephalopods may have measured 25 to 35 feet (8 to 11 meters) long. Like the modern giant squid, Tusoteuthis lacked an outer shell and is known only from discoveries of the rigid support structure in its body called a pen or gladius. The pen was akin to a backbone but made of delicate shell-like material called chitin.
The pen supported a fleshy body with large eyes, a sharp beak, and presumably ten arms lined with suckers that made Tusoteuthis a formidable predator in the Late Cretaceous seas. Smaller cephalopods and fish were likely dietary staples, though small marine reptiles that visited the ocean depths may have fallen prey as well.
Tusoteuthis moved via jet propulsion—it expelled water through a siphon on the lower part of its body. Squirts of dark inky fluid sometimes helped the squid blind and confuse predators like the mosasaur Tylosaurus and a barracuda-like fish called Cimolichthys long enough for escape.