By: Jason Prater

What environmental factors are responsible for driving this transition?

Evolution of whale hearing?

Whales, dolphins, and porpoises Characteristics:

Obligate aquatic species Flippers Fluke Vestigial hind limbs

Artiodactyls

Indohyus Found in India Small deer-like Wading mammal

Cenozoic Cooling Upwelling of

nutrients

Antarctic Circumpolar Current Flows west to east

around Antarctica Nutrient exchange

between Atlantic, Pacific, and Indian Ocean.

Building of cell walls, or frustules, in diatoms Increased diatom diversity in Cenozoic Era

Diatoms Unicellular Producers One of the Most common types of phytoplankton Eaten by Krill

Krill then eaten by whales Short food chain (efficient in supporting apex

predator)

Evolved very quickly Pakicetids (basal cetacean group)

Similar to land mammals External auditory meatus tympanic

membrane middle ear ossicles inner ear fluid Fails under water.

Remingtonocetids and Protocetids Combination of pakicetids and modern

odontocetes Sound transmitted to middle ear by large

mandibular fat pad Presence of external auditory meatus

But poor reception of airborne sound Basilosauroids

Addition of air-filled sinuses between ear and skull Still contained external auditory meatus even

though they were obligate marine animals. Modern Odontocetes

Loss of external auditory meatus

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of whales: macroevolution documented on the Indian subcontinent. Journal of Bioscience. Nov. 34(5):673-686, 2009.

J.G.M. Thewissen, L.N. Cooper, M.T. Clementz, S. Bajpai and B.N. Tiwari. Whales originated from aquatic Aritiodactyls in the eocene epoch of India. Nature 450, 1190-1194. 2007

Marx, F.G. and M. Uhen. Climate, critters, and cetaceans: Cenozoic driers of the evolution of modern whales. Science 327, 993-996, 2010. 

Berger, W.H. Cenozoic cooling, Antarctic nutrient pump, and the evolution of whales. Oceanograhy. 54, 2399. 2007