According to a short communication recently published in the Journal of Vertebrate Paleontology, an ancient marine reptile provided a feast for hungry sharks.
In 2006 paleontologists Tamaki Sato, Yoshikazu Hasegawa and Makoto Manabe described the remains of a previously-unknown kind of elasmosaurid, Futabasaurus suzukii, a long-necked predator that swam the seas in what is now Japan about 85 million years ago. Despite its role at the top of the food web, though, many of the bones of Futabasaurus bore toothmarks, and at least 82 shark teeth were found around the skeleton. There were even several shark teeth embedded in the skeleton. Not only had the scientists found a new marine reptile, but they had stumbled upon a prehistoric shark buffet.
According to the new analysis, the shark teeth belong to the species Cretalamna appendiculata, a shark that belonged to the group that contains modern great white, mako and sand tiger sharks. The question is whether the sharks attacked the plesiosaur or were scavenging its carcass. Even though it had previously been proposed that the elasmosaur remains recorded an attack by multiple sharks, the authors of a new study converge on a different scenario.
While the elasmosaur's cause of death is unknown, it appears that it sank to the bottom and was left uncovered for a short period of time, no more than a few months. (The fact that much of the skeleton remained articulated argues against the "bloat and float" scenario in which a decomposing carcass wells with gas, floats to the surface, and begins to drop body parts over a wide area as it rots or is scavenged.) During this time multiple sharks (at least six) fed upon it, and while the carcass may have been the site of a shark "feeding frenzy," it is impossible to tell when each individual shark came and fed. Despite these uncertainties, however, this specimen of Futabasaurus is remarkable because it contains the fleeting records of life, death and scavenging during a time tens of millions of years before our own.
Shimada, K., Tsuihiji, T., Sato, T., & Hasegawa, Y. (2010). A Remarkable Case of a Shark-Bitten Elasmosaurid Plesiosaur Journal of Vertebrate Paleontology, 30 (2), 592-597 DOI: 10.1080/02724631003621920