Skulls (image) University of Michigan Caption Evolutionary relationships between terrestrial even-toed hoofed mammals (artiodactyls), Eocene archaeocete whales, and modern toothed and baleen whales. The skulls of archaeocetes and toothed whales are asymmetrical, but the skulls of artiodactyls and baleen whales are symmetrical. Asymmetry evolved in archaeocetes and was later exaggerated in toothed whales. Asymmetry was reduced in baleen whales. Credit Credit: Julia M. Fahlke Usage Restrictions None Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.