Despite this giant squid pen's shabby appearance, it is quite a remarkable fossil. A squid pen, also called a gladius, is an internal bone-like structure that gives support to a squid's mantle and provides a place for muscle attachment. Squids are made mostly of soft tissue and only have two hard parts: their beak-like mouthparts and their gladius. Hard parts are more likely to be preserved as fossils than soft tissue as hard parts are more resistant to decay than soft tissue. The only way paleontologists know for certain that Tusoteuthis lived in the late Cretaceous Western Interior Seaway about 70 million years ago is from finding fossilized squid pens like this specimen.
Although squid pens—and very rarely, squid beaks—are often the only remains that can be found of ancient squids, paleontologists are able to infer how Tusoteuthis lived from these remains. Studying this specimen and other fossils from the Western Interior Seaway help to reconstruct what life was like in the late Cretaceous seaway.
The Western Interior Seaway existed in a time when there was no polar ice, and sea surface temperatures were estimated to be around 20°C (about 68°F) . As a result, sea level was over 150 meters (about 164 yards) higher than today, which caused the inundation of what is now the North American West. The Western Interior Seaway extended about 4900 km (3044 miles) from the Canadian Arctic to the proto-Gulf of Mexico and whose width is estimated to have been about 1000 km (620 miles, approximately the distance from the Colorado Front Range to western Missouri).
Tusoteuthis is estimated to have grown up to 11 meters in length and fed mostly on fish . While giant in size, some paleontologists believe that Tusoteuthis was more closely related to the modern vampire squid, Vampyroteuthisi, than to the modern giant squid, Architeuthis . Other creatures common in the Western Interior Seaway were mosasaurs, fish, ammonites, and bivalves. Many of the Western Interior Seaway creatures, including Tusoteuthis, are extinct today.
The University of Colorado Museum of Natural History has over 3000 specimens from the late Cretaceous Western Interior Seaway—six of these specimens are squid pens of Tusoteuthis. The Museum has a great representation of Western Interior Seaway fauna and its collection is one of the best places to see examples of past life of the Western Interior Seaway.
 He, S., Kyser, T.K., Caldwell, W.G.E., 2005, Paleoenvironment of the Western Interior Seaway inferred from Δ18O and Δ13C values of molluscs from the Cretaceous Bearpaw marine cyclothem: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 217, p. 67-85.
 Eyden, Phil, 2006, Tusoteuthis and the Cretaceous Giant Squids: The Octopus News Magazine Online.
 Engeser, T., and J. Reitner, 1986, Coleoidenreste aus der Oberkreide des Libanon imStaatlichen Museum für Naturkunde in Stuttgart: Stuttgarter Beiträge zurNaturkunde, Serie B (Geologie und Paliiontologie), v. 124, p. 1-15.