why did whales evolve

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Over the course of cetacean evolutionary history, the oceans and shallow seas of earth were undergoing a series of transformations. Scientists believe that the Microchiroptera likely evolved from small gliding mammals of the order Insectivora. Whale Evolution Part of the Whales: Giants of the Deep exhibition. It was presented as a stumpy-legged, seal-like creature, an animal caught between worlds. There was no straight-line march of terrestrial mammals leading up to fully aquatic whales, but an evolutionary riot of amphibious cetaceans that walked and swam along rivers, estuaries and the coasts of prehistoric Asia. Looking at a whale’s body and biology, there are plenty of clues that their ancestors lived on land. His attention to such tiny details ultimately settled the identification of the sea monster. The fossil record was so sparse that no definite determination could be made, but in a thought experiment included in On the Origin of Species, Darwin speculated about how natural selection might create a whale-like creature over time: In North America the black bear was seen by [the explorer Samuel] Hearne swimming for hours with widely open mouth, thus catching, like a whale, insects in the water. A few years later, a scientist handling a different specimen with his colleagues pulled out a bone from the skull, dropped it, and it shattered on the floor. He tentatively assigned it the name Basilosaurus. Mesonychids were not the ancestors of whales, and hippos are now known to be the closest living relatives to whales. They had long skulls and large carnivorous teeth. Writing to his staunch advocate T.H. Copyright 2010. Give a Gift. The skull of Pakicetus exhibited just this condition. However, their skulls particularly in the ear region, which is surrounded by a bony wall strongly resemble those of living whales and are unlike those of any other mammal. The skull of Basilosaurus had more in common with ancient “pig-like Ungulates” than seals, thus giving the common name for the porpoise, “sea-hog,” a ring of truth. Whales evolved … Privacy Statement Collect. Just like humans, whales can become grandmothers while they're still having babies themselves. Study of the rest of the skeleton also revealed that Indohyus had bones marked by a similar kind of thickening, an adaptation shared by mammals that spend a lot of time in the water. The astounding transition came shortly after the rise of modern mammal groups, around 55 million years ago, during a hot period in the Earth’s history. Asked by Wiki User. or NEW YORK — By moving into the water full-time, the ancestors of whales paved the way for their descendants to become behemoths, largely free … Even better, two jaw fragments showed that the teeth of Pakicetus were very similar to those of mesonychids. Hippos likely evolved from a group of anthracotheres about 15 million years ago, the first whales evolved over 50 million years ago, and the ancestor of both these groups was terrestrial. Over time their descendants spent more and more time in the water and their bodies became adapted for swimming. Vote Now! However, have you ever stopped to consider how they came to be what we know them as today? 17th Annual Photo Contest Finalists Announced. Both hippos and whales evolved from four-legged, even-toed, hoofed (ungulate) ancestors that lived on land about 50 million years ago. The of adaptation of cetaceans and other mammals to the oceans may be similar to that of the hippopotamus. Dive deeper into the world of whales and dolphins and learn more about their lives. Often called “wolves with hooves,” mesonychids were medium- to large-sized predators with long, toothy snouts and toes tipped with hooves rather than sharp claws. Whales evolved from early land mammals, adapting to life in the oceans by losing their hind-limbs, growing a flat tail, developing flippers and streamlining their bodies. These first whales, such as Pakicetus, were typical land animals. This basic concept, evolving to fill available niches, is a common outcome of the evolutionary process. Top Answer. But, because they are mammals, we know that they must have evolved from land-dwelling ancestors. The jaw contained teeth that differed in size and shape, a characteristic of mammals but not most reptiles. Like Basilosaurus, though, Squalodon was fully aquatic and provided few clues as to the specific stock from which whales arose. In 1832, a hill collapsed on the Arkansas property of Judge H. Bry and exposed a long sequence of 28 of the circular bones. A startling discovery made in the arid sands of Pakistan announced by University of Michigan paleontologists Philip Gingerich and Donald Russell in 1981 finally delivered the transitional form scientists had been hoping for. They were major predators in the Northern Hemisphere from shortly after the demise of the dinosaurs until about 30 million years ago, and the shape of their teeth resembled those of whales like Protocetus. By the turn of the 20th century the oldest fossil whales were still represented by Basilosaurus and similar forms like Dorudon and Protocetus, all of which were fully aquatic—there were no fossils to bridge the gap from land to sea. They breathe air and nurse their young with their own milk, they also have paddle-shaped flippers which encase hand bones with five ‘fingers’. Some of the sediment attached to the bone contained small shells that showed that the large creature had once lived in an ancient sea, but little more could be said with any certainty. There were three attempts to keep grey whales in captivity. 1846. Together these fossil whales hung in a kind of scientific limbo, waiting for some future discovery to connect them with their land-dwelling ancestors. These prehistoric whales were more elongated than modern whales and had small back legs and front flippers. Studies coming out of the field of molecular biology conflicted with the conclusion of the paleontologists that whales had evolved from mesonychids, however. Terms of Use Harlan traveled to London in 1839 to present Basilosaurus to some of the leading paleontologists and anatomists of the day. Though these creatures, such as Dimetrodon, looked like reptiles, they were actually the archaic precursors of mammals. Hippos are the closest living relatives of whales, but they are not the ancestors of whales. As some of these creatures began to feed on a different diet, they evolved into baleen filter feeders and lost their teeth. When the genes and amino acid sequences of living whales were compared with those of other mammals, the results often showed that whales were most closely related to artiodactyls—even-toed ungulates like antelope, pigs, and deer. With whales being mammals, and mammalian ancestors being land animals, whale ancestors must have lived on land too. Bry’s donation was soon matched, and even exceeded, by that of Judge John Creagh from Alabama. Basilosaurus did share some traits with marine reptiles, but this was only a superficial case of convergence—of animals in the same habitat evolving similar traits—because both types of creature had lived in the sea. Another extinct whale called Squalodon, a fossil dolphin with a wicked smile full of triangular teeth, similarly hinted that whales had evolved from meat-eating ancestors. Living at about the same time as the remingtonocetids was another group of even more aquatically adapted whales, the protocetids. Now, a group of scientists have investigated the changes in 85 different genes that were lost in this land-to-sea transition. Whale Evolution and Fossils. From the orca to the tiny vaquita, learn more about these creatures. He thought they might be of scientific interest and sent a package to the American Philosophical Society in Philadelphia. Gigi was a grey whale calf that died in transport. Huxley in 1871, Darwin asked whether the ancient whale might represent a transitional form. No one quite knew what to make of them. This shift allowed the fully aquatic whales to expand their ranges to the shores of other continents and diversify, and the sleeker basilosaurids like Dorudon, Basilosaurus and Zygorhiza populated the warm seas of the late Eocene. While preparing the underside of the skull of Indohyus, a student in Thewissen’s lab broke off the section covering the inner ear. Smithsonian Institution, (From Fowler, O.S. Which were more reliable, teeth or genes? Now the tide has turned. Fish-eating orcas can feed on salmon or … As strange as modern whales are, their fossil predecessors were even stranger. Share. The fact that it was found in freshwater deposits and did not have specializations of the inner ear for underwater hearing showed that it was still very early in the aquatic transition, and Gingerich and Russell thought of Pakicetus as “an amphibious intermediate stage in the transition of whales from land to sea,” though they added the caveat that “Postcranial remains [bones other than the skull] will provide the best test of this hypothesis.” The scientists had every reason to be cautious, but the fact that a transitional whale had been found was so stupendous that full-body reconstructions of Pakicetus appeared in books, magazines and on television. Huxley thought that Basilosaurus at least represented the type of animal that linked whales to their terrestrial ancestors. Cope admitted in an 1890 review of whales: “The order Cetacea is one of those of whose origin we have no definite knowledge.” This state of affairs continued for decades. The Florida Department of Education has some suggested ideas on how to teach High School students about the evolution of the whale. Fossils of gigantic ancient whales called Basilosaurus were first mistaken for dinasaur fossils but were later recognised as mammals. Van Valen hypothesized that some mesonychids may have been marsh dwellers, “mollusk eaters that caught an occasional fish, the broadened phalanges [finger and toe bones] aiding them on damp surfaces.” A population of mesonychids in a marshy habitat might have been enticed into the water by seafood. Support WDC by shopping for yourself or a friend. > How did whales evolve? The earliest known archaeocetes were creatures like the 53-million-year-old Pakicetus and the slightly older Himalayacetus. Mammals diversified in the shadow of the great archosaurs, and they remained fairly small and secretive until the non-avian dinosaurs were wiped out by a mass extinction 65 million years ago. One particular ankle bone, the astragalus, had the potential to settle the debate. About 34 million years ago, a group of whales began to develop a new way of eating. He envisioned a hypothetical cetacean ancestor easing itself into the shallows: We may conclude by picturing to ourselves some primitive generalized, marsh-haunting animals with scanty covering of hair like the modern hippopotamus, but with broad, swimming tails and short limbs, omnivorous in their mode of feeding, probably combining water plants with mussels, worms, and freshwater crustaceans, gradually becoming more and more adapted to fill the void place ready for them on the aquatic side of the borderland on which they dwelt, and so by degree being modified into dolphin-like creatures inhabiting lakes and rivers, and ultimately finding their way into the ocean. Series of transformations and you may have studied about them with their land-dwelling ancestors not like the 46-million-year-old.... 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