Which group of marine reptiles had a dolphin-like body and large eyes?

The group of marine reptiles with dolphin-like bodies and large eyes was the ichthyosaurs. These streamlined reptiles evolved bodies suited to fast swimming, with pointed snouts, flippers, and powerful tail fins.

Ichthyosaurs were not dinosaurs, despite living during much of the same broad era. They were air-breathing reptiles that spent their entire lives in the sea. Many species gave birth to live young rather than laying eggs on land, an adaptation that removed the need to leave the water.

Their very large eyes were especially useful for seeing in dim conditions, including deeper water. Some ichthyosaurs had enormous eyes supported by strong bony rings, suggesting that vision played an important role in hunting. Their diets included fish, squid-like animals, and other marine prey, although some large species may have tackled bigger animals.

The other choices were also marine reptiles, but they had different body plans. Mosasaurs were generally lizard-like, plesiosaurs had distinctive neck-and-flipper arrangements, and pliosaurs were short-necked predators with large heads. Ichthyosaurs are the classic dolphin-shaped group.