"This finding challenges our understanding of body-size evolution," J. G. M. Thewissen and David A. Waugh write in a
Whales, dolphins and porpoises belong to a group called cetaceans, which includes the largest known animals that ever lived, the two scientists write. Until now it had been assumed that the blue whale holds the record for the largest body size. The whale is modeled from a partial skeleton, which includes 13 vertebrae, four ribs and one hip bone. Each vertebra weighs more than 220 pounds, and its ribs measure nearly 5 feet long.According to the study, the whale is a member of the basilosaurid group, a family of extinct cetaceans. It not only was extremely large, but it also had an exceptionally heavy skeleton relative to its body mass.