The following image shows the biological evolution that happened with Ichthyosaur and how they turned to become Dolphin. Based on the Ichthyosaur fossil's discovery, Ichthyosaur species varied from 1 to 20 meters (3 to 66 ft) in length. Ichthyosaurs resemble both modern fish and dolphins. Their limbs had been fully transformed into flippers, which sometimes contained a very large number of digits and phalanges. At least some species possessed a dorsal fin. Their heads were pointed, and the jaws were often equipped with conical teeth that could help catch smaller prey. Similar to Ichthyosaur, we also have a similar biological evolution of Dolphins.