Evolution of cetaceans "Caperea marginata") all have derived characteristics presently unknown in any cetothere and vice versa (such as a sagittal crest). The adaptation of echolocation occurred when toothed whales (Odontoceti) split apart from baleen whales, and distinguishes modern toothed whales from fully aquatic archaeocetes. This happened around 34 million years ago in a second cetacean radiation. Modern toothed whales do not rely on their sense of sight, but rather on their sonar to hunt prey. Echolocation also allowed toothed whales to dive deeper in search of food, with light no longer necessary for navigation, which opened up new food sources. Toothed whales
Two Forms (Divided Circle) fire at her studio in St Ives in 1975. It includes two vertical bronze semi-circles forming a broken circle approximately across, each pieced pierced by one large hole. Both elements are welded to a bronze base. All three elements are hollow, and were cast in London by Morris Singer. Hepworth designed the work after being diagnosed with cancer in 1966. She wanted the viewer's body to be engaged with her work, saying: "You can climb through the Divided Circle – you don't need to do it physically to experience it." Hepworth also made a series of nine maquettes about tall,