| Summary: | The Oligocene record for Cetacea is quite poor in comparison to the Eocene and the Miocene. However, the initial and rapid radiation Of the Odontoceti (toothed whales) and the Mysticeti (baleen whales) occurred in the Oligocene, and this is considered to be an important period in the evolution of these modern suborders. 2 Odontocetes and mysticetes developed very specialised cranial features related to feeding: mysticetes developed baleen plates to filter-feed plankton, and odontocetes developed the ability to echolocate to aid in hunting and navigation. The observation of the zoogeography of modern whales and their dependence on nutrient-rich upwell areas has led to the hypothesis that the evolution of whales in the Oligocene is a result of new, abundant food resources in upwelling areas resulting from changing ocean currents and shifting continents. The break-up of Gondwanaland and the formation of the cool Southern Ocean could be important factors relating to this. The Oligocene record for Cetacea is quite poor in comparison to the Eocene and the Miocene. However, the initial and rapid radiation Of the Odontoceti (toothed whales) and the Mysticeti (baleen whales) occurred in the Oligocene, and this is considered to be an important period in the evolution of these modern suborders. 2 Odontocetes and mysticetes developed very specialised cranial features related to feeding: mysticetes developed baleen plates to filter-feed plankton, and odontocetes developed the ability to echolocate to aid in hunting and navigation. The observation of the zoogeography of modern whales and their dependence on nutrient-rich upwell areas has led to the hypothesis that the evolution of whales in the Oligocene is a result of new, abundant food resources in upwelling areas resulting from changing ocean currents and shifting continents. The break-up of Gondwanaland and the formation of the cool Southern Ocean could be important factors relating to this.
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