Evolutionary history Sperm whale

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fossil record

although fossil record poor, several extinct genera have been assigned clade physeteroidea, includes last common ancestor of modern sperm whale, pygmy sperm whales, dwarf sperm whales, , extinct physeteroids. these fossils include ferecetotherium, idiorophus, diaphorocetus, aulophyseter, orycterocetus, scaldicetus, placoziphius, zygophyseter , acrophyseter. ferecetotherium, found in azerbaijan , dated late oligocene (about 28 to 23 million years ago), primitive fossil has been found possesses sperm whale-specific features such asymmetric rostrum ( beak or snout ). sperm whale fossils date miocene period, 23 to 5 million years ago. diaphorocetus, argentina, has been dated miocene. fossil sperm whales middle miocene include aulophyseter, idiorophus , orycterocetus, of found on west coast of united states, , scaldicetus, found in europe , japan. orycterocetus fossils have been found in north atlantic ocean , mediterranean sea, in addition west coast of united states. placoziphius, found in europe, , acrophyseter, peru, dated late miocene.


fossil sperm whales differ modern sperm whales in tooth count , shape of face , jaws. example, scaldicetus had tapered rostrum. genera oligocene , , middle miocene, possible exception of aulophyseter, had teeth in upper jaws. acrophyseter, late miocene, had teeth in both upper , lower jaws short rostrum , upward curving mandible (lower jaw). these anatomical differences suggest fossil species may not have been deep-sea squid eaters modern sperm whale, genera ate fish. zygophyseter, dated middle late miocene , found in southern italy, had teeth in both jaws , appears have been adapted feed on large prey, rather modern orca (killer whale). other fossil sperm whales adaptations similar collectively known killer sperm whales.


phylogeny

the traditional view has been mysticeti (baleen whales) , odontoceti (toothed whales) arose more primitive whales in oligocene period, , super-family physeteroidea, contains sperm whale, dwarf sperm whale, , pygmy sperm whale, diverged other toothed whales after that, on 23 million years ago. 1993 1996, molecular phylogenetics analyses milinkovitch , colleagues, based on comparing genes of various modern whales, suggested sperm whales more closely related baleen whales other toothed whales, have meant odontoceti not monophyletic; in other words, did not consist of single ancestral toothed whale species , descendants. however, more recent studies, based on various combinations of comparative anatomy , molecular phylogenetics, criticised milinkovitch s analysis on technical grounds , reaffirmed odontoceti monophyletic.


these analyses confirm there rapid evolutionary radiation (diversification) of physeteroidea in miocene period. kogiidae (dwarf , pygmy sperm whales) diverged physeteridae (true sperm whales) @ least 8 million years ago.









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