![]() This trend has continued into living whales, which have a “blowhole” (the exterior opening to the bony nostrils) located on top of the head above the eyes. These animals evolved nostrils positioned further and further back along the snout. Whales that evolved after Ambulocetus ( Kutchicetus, etc.) show even higher levels of saltwater oxygen isotopes, indicating that they lived in nearshore marine habitats and were able to drink saltwater as today’s whales can. ![]() Isotopic analyses help us figure out the likely habitats of extinct whales like Ambulocetus. The isotopes show that Ambulocetus likely drank both saltwater and freshwater, which fits perfectly with the idea that these animals lived in estuaries or bays between freshwater and the open ocean. This means that we can learn about what sort of water an animal drank by studying the isotopes that were incorporated into its bones and teeth as it grew. Animals are what they eat and drink, and saltwater and freshwater have different ratios of oxygen isotopes. The hypothesis that Ambulocetus lived an aquatic life is also supported by evidence from stratigraphy - Ambulocetus‘s fossils were recovered from sediments that probably comprised an ancient estuary - and from the isotopes of oxygen in its bones. Its tail is longer and more muscular, too. Its legs are shorter, and its hands and feet are enlarged like paddles. Evolution: Education & Outreach 2:272-288.Ĭompared to other early whales, like Indohyus and Pakicetus, Ambulocetus looks like it lived a more aquatic lifestyle. From land to water: The origin of whales, dolphins, and porpoises. Photo of Pakicetus and Ambulocetus courtesy of J.G.M. Often, seemingly minor features provide critical evidence to link animals that are highly specialized for their lifestyles (such as whales) with their less extreme-looking relatives. However, their skulls - particularly in the inner ear region, which is surrounded by a bony wall - strongly resemble those of living whales and are unlike those of any other mammal. From the outside, they don’t look much like whales at all. They had long skulls and large teeth that could be used for eating meat. These first whales, such as Pakicetus, were typical land animals. Hippos likely evolved from a group of anthracotheres about 15 million years ago, the first whales evolved over 50 million years ago, and the ancestors of both these groups were terrestrial. Nor were the ancient relatives of whales that you see pictured on this tree - such as Pakicetus. We know this because the ancient relatives of hippos called anthracotheres (not shown here) were not large or aquatic. ![]() Hippos are large and aquatic, like whales, but the two groups evolved those features separately from each other. Whale phylogeny from The Tangled Bank, used with permission of the author, Carl Zimmer, and publisher, Roberts & Company, Greenwood Village, Colorado. That’s why each of them gets its own branch on the family tree. In fact, none of the individual animals on the evogram is the direct ancestor of any other, as far as we know. The first thing to notice on this evogram is that hippos are the closest living relatives of whales, but they are not the ancestors of whales.
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