Catie Willard and Lindsey Baumoel
Question???How have whales
physiologically evolved from land to water?
Whale Video
PakicetusThree genera:
Pakicetus, Nalacetus, and Ichthyolestes
Eocene Kuldana Formation of Pakistan
Evidence of Fossils
Ambulocetus47-48 million years
agoWell developed fore-
and hind-limbsSwam by pelvic
paddlingHind feet large, with
elongated, flattened toes suggesting webbed feet and the ability to walk on land
DorudonLate-middle EoceneSmaller dolphin-
sized animalsSkeletal morphology
of caudal regionNo sacrum and
floating pelvis
Basilosaures40 to 34 million years
agoHind limbs to short to
support body mass18 meters (60 feet)The hind limbs had
fused tarsalsAbsence of
articulationPossible functions of
limbs
Mysticeti and OdontocetiMioceneHave baleen teeth
used for filter-feeding
Very large and do not dive to great depths
Typically smaller than baleen whales
Have teethSwim rapidly and
dive deep
Molecular EvidenceFive mitochondrial DNA sequences and eleven nuclear-
encoded protein sequences aligned from Cetacea, two Artiodactyl suborders and an outgroup
Cetacean DNA sequences from Finback WhaleProtein 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 sequencesStatistical tests Cow-Pig Cow-Cetacean Pig-Cetacean
PARS 641 624 641
ML 0 89 11
Molecular EvidencePROTPARS 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
ResultsTree one is the presently accepted taxonomic
schemeThe 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 CitedBejder, 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’dGraur, 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.
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