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Animal Evolution Response to a changing environment The Beginning Evidence from fossil animals and plants indicate that environments have changes over time and that animal populations change as well. Horses: Ancestors of horses are thought to have started out as forest dwelling animals, living on soft, wet forest floors and eating plants. In a wet forest environment having a foot that can spread out is an advantage. But on a dryer, harder surface a foot that can help you run fast on that surface is an advantage. That foot has fewer toes and a hard nail or hoof to run on. Some horse ancestors had slightly harder and bigger teeth than others – these tended to more effectively eat these “harder” leaves, and had greater reproductive success. Horse teeth also became longer, having more length in the jaw bone. So, horses changed along with their environment Whale Evolution In comparing a whale to a fish, we can see that each lineage is adapted to swim in the oceans, but in very different ways. Why are they different? (We know that whales are mammals.) Whale Questions What are Whales? Where did whales “come from”? What evidence do we have regarding the evolution of whales? What’s a whale? Fish: Whale: Why don’t these skeletons look the same? What is the ‘floating bone’ circled here? Whale Hips Time Early Whale Teeth (in a 4-legged mammal?) a Mesonychid –called Pachyaena … with tiny hooves! ~ 55 mya Early Whale Teeth ~50 mya Pakicetus - an early whale Early Whale Teeth… With tiny hooves, too ! Ambulocetus - the “walking whale” ~48 mya Early Whale Teeth Rodhocetus - an early whale And tiny hooves, too ! ~46 mya Early whale teeth in… Basilosaurus and LEGS too… ~37mya Early Whale Teeth in Dorudon ~ 36 mya Ambulocetus DNA Analysis of a Whale and EvenToed Ungulates compare segments of beta-casein gene Whale Evolution Recap Fossil teeth link whales to the 4-legged mesonychids of the Paleo-Eocene. Tiny hooves on mesonychids and early whale toes tie whales to the ungulates. Ankle bones of early whales point to artiodactyl ungulates as the closest relatives of whales. DNA differences point to hippos as the closest living relative of modern whales. Whale’s Closest Cousin: Hippos