Transcript 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
 Typically smaller than
 Have baleen teeth used
baleen whales
 Have teeth
 Swim rapidly and dive
deep
for filter-feeding
 Very large and do not
dive to great depths
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
Statistical tests
Cow-Pig
Cow-Cetacean
Pig-Cetacean
PARS
641
624
641
ML
0
89
11
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.