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 • Evidence of Fossils
Ambulocetus • 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
Dorudon • Late-middle Eocene • Smaller dolphin-sized animals • Skeletal morphology of caudal region • No sacrum and floating pelvis
Basilosaures • 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
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
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
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
Results • 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
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.
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.