Transcript Whale transitions from land to water

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





Sirpa Nummela, J.G.M. Thewissen, Sunji Bajpai, S. Taseer Hussain and
Kishor Kumar. Eocene Evoluiton of Whale Hearing. Nature 430, 776-778.
2004.
Bajpai, S. Thewissen J.G., Sahni, A. The origin and early evolution 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