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Evolution of Whales: From Land to Water. Catie Willard and Lindsey Baumoel. Question???. How have whales physiologically evolved from land to water?. Whale Video. Pakicetus. Three genera: Pakicetus , Nalacetus , and Ichthyolestes Eocene Kuldana Formation of Pakistan

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Evolution of whales from land to water l.jpg

Evolution of Whales: From Land to Water

Catie Willard and Lindsey Baumoel

Question l.jpg

How have whales physiologically evolved from land to water?

Whale Video

Pakicetus l.jpg

  • Three genera: Pakicetus, Nalacetus, and Ichthyolestes

  • Eocene Kuldana Formation of Pakistan

  • Evidence of Fossils

Ambulocetus l.jpg

  • 47-48 million years ago

  • Well developed fore- and hind-limbs

  • Swam by pelvic paddling

  • Hind feet large, with elongated, flattened toes suggesting webbed feet and the ability to walk on land

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  • Late-middle Eocene

  • Smaller dolphin-sized animals

  • Skeletal morphology of caudal region

  • No sacrum and floating pelvis

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  • 40 to 34 million years ago

  • Hind limbs to short to support body mass

  • 18 meters (60 feet)

  • The hind limbs had fused tarsals

  • Absence of articulation

  • Possible functions of limbs

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Mysticeti and Odontoceti

  • Miocene

  • Have baleen teeth used for filter-feeding

  • Very large and do not dive to great depths

  • Typically smaller than baleen whales

  • Have teeth

  • Swim rapidly and dive deep

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Molecular Evidence

  • Five mitochondrial DNA sequences and eleven nuclear-encoded protein sequences aligned from Cetacea, two Artiodactyl suborders and an outgroup

  • Cetacean DNA sequences from Finback Whale

  • Protein sequences come from different whales depending on who the sequence was known for in each of the eleven proteins

  • Maximum parsimony and maximum likelihood where the methods of reconstruction used for alternative phylogenetic trees

  • Only transversions were looked at for the DNA sequences

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Molecular Evidence

  • PROTPARS was used to calculate the number of amino acid replacements required for each alternative tree

  • The reliability of these tests was determined by bootstrap re-sampling of parsimony and several other tests; for DNA sequences the max-likelihood trees were also tested by bootstrap re-sampling

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  • Tree one is the presently accepted taxonomic scheme

  • The DNA data using max parsimony and max likelihood combined with bootstrap resampling gives tree II

  • For protein sequences the traditional tree was not supported by any of the tests; the only significant support was for tree II

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Works Cited

  • Bejder, Lars and Brian K. Hill. 2002. Limbs in whales and limblessness in other vertebrates: mechanisms of evolutionary and developmental transformation and loss. Evolution and Development. 4(6): 445-458.

  • Gingerich, Philip D. 2003. Land-to-sea transition in early whales: evolution of Eocene Archaeoceti (Cetacea) in relation to skeletal proportion and locomotion of living semiaquatic. Paleobiology. 29(3): 429-454.

  • Gingerich, Philip D. 1998. Paleobiological perspectives on Mesonychia, Archaeoceti, and the origin of whales. Paleobiology. 423-446.

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Works Cited cont’d

  • Graur, D. and Higgens, D. 1994. Molecular evidence for the inclusion of cetaceans within the order artiodactyla. Mol. Biol. Evol. 11(3): 357-364.

  • Thewissen, J. G. M., Hussain, S. T., and Arif, M. 1994. Fossil evidence for the origin of aquatic locomotion in Archalocete whales. Science. 263(5144): 210-212.

  • Thewissen, J. G. M, Williams, E. M., Roe, L. J., and Hussain, S. T. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature. 413: 277-281.