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The ancestors of cetaceans began to move into the water and develop aquatic characteristics about 50 million years ago. They have been evolving ever since, gradually becoming more and more aquatic. Today's cetaceans live entirely in water. The ancestors of pinnipeds began moving into water much more recently, about 23 million years ago. Because of this, modern pinnipeds are not as fully aquatic as cetaceans. The ancestors of sirenians began moving into the water about 40 million years ago, and have been evolving since then.
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Why is there a much greater diversity of flying birds than there is of flying mammals?
Think of it as the same thing as land mammals versus water mammals. Marine mammals first evolved to life on land and then adapted to return to the water, but not all mammals did that. Similar thing with birds. All birds evolved from common flying ancestors, whereas flying mammals evolved from land mammals at a much later point in evolutionary history. Hope that helps.
What mammals do not live on land and do not lay eggs?
Marine mammals do not live on land, and no marine mammals lay eggs. Marine mammals include whales, dolphins and porpoises.
Are marine mammal dorsal fins genes derived from fish dorsal fin genes?
No. The fins evolved from land ancestors who went into the water. This have nothing to do with fish.
What were the first marine mammals to evolve?
Marine mammals such as whales, dolphins and porpoises, are collectively labelled cetaceans (of the order Cetacea, comprising 87 modern species). Cetaceans appear to have evolved from a land mammal that began adapting to marine environments 50,000,000 years ago; the earliest known 'proto whale' (ancestor of modern Cetaceans) is named Pakicetus- a land-based quadruped that eventually evolved into Ambulocetus, which lived in shallow waters but were still able to walk on land.
What is the difference among marine mammals and other mammals?
Marine mammals live and water and they need to surface to breathe. While land mammals can breathe just as humans do.
How did reptiles pave the way for more land animals?
With skin and egg shells able to retain water, reptiles could remain out of water indefinitely, unlike their amphibian ancestors. Mammals and dinosaurs (from which birds evolved) later evolved from reptiles.
How do animals evolve to marine animals if their ancestors were land animals?
well over time the land animals change a little and they need to be underwater to live unlike their land animal ancestors
Did whales ever walk the earth?
Not as whales, no. Marine (sea) mammals (whales, dolphins, etc.) are descended from terrestrial (land) mammals, but they're not identical with those land mammals... among the more obvious changes, they've lost their legs. The related links section has a link to a Wikipedia page showing what some of the distant ancestors of whales might have looked like.
An animal that lives in the ocean but whose ancestors millions of years ago walked on land is?
Land dwelling mammals called archaeocetes evolved to live in the ocean around 50 million years ago. Their descendants include dolphins and whales. Sea turtles, also, evolved from land dwelling turtles more than 110 million years ago.
What is an example of an organ systems whose anatomical features differ entirely in function found in mammals than in their non-mammalian ancestors?
Most tetrapods -- including pre-human mammals -- originated in water and have since evolved to function on land. As such, substantial anatomical chance has occurred.
What evidence supports the hypothesis that whales evolved from land-dwlling mammals?
Theory of evolution
What is the largest land mammal to ever live?
There are no land mammals in or on Antarctica. There are only marine mammals.
