By the Upper Triassic they are similar in shape to dolphins and to fast predatory fish like tuna (convergent evolution). They are found in marine strata from the earliest Triassic to the Cretaceous, though the early proto-ichthyosaurs are sometimes put in the broader category of Ichthyopterygia. After transitional Triassic types like "Mixosaurus" and "Cymbospondylus", they have essentially the same body shape. "Californosaurus" was one of the first to have the typical dolphin-like body shape.