Transcript Cetacean Evolution

Cetacean Evolution
What is the exact ancestor of
cetaceans?
•
•
•
•
DNA evidence supports
Whales and Hippos 1st cousins
Whales and Hippos into H2O 55 mya
DNA/ DNA hybridization
Analyze (compare DNA)
Studied by molecular Biologists
– But anklebones (fossil evidence0 don’t support this
idea. But whales don’t have anklebones, or do
they?
52 mya, Packicetus (Pakistan):
• Skull of an “archeocyte” (now extinct)
• Cetacean- like but jaw different
– 1) Have ears- no oil filled space for receiving sound
in H20
– 2) No blowhole
• Fed in fish in shallow water
• Bred and gave birth on land
• Wolf size to bear size
Fossil evidence studied by paleontologists
49 mya, Ambulocetus natans
(Pakistan):
•
•
•
•
Means “walking whale that swam”
Strong legs with feet like pinniped (kind of sea)
No fluke yet
Flexible backbone. Swam by undulating body
up and down, like sea lion
– Bred and gave birth on land
40 mya, Brachiosaurus 50’ long
(Egypt):
• Many skeletons discovered
• Simple hind leg with three tiny toes used as
“claspers” to hold female during mating
• Carnivorous teeth
• Hair reduced/ lost to decrease drag
• Breathing nostrils move toward top of head
Basiloaurus
•
•
•
•
•
•
Toothed whales - odontocetes
Killer whale
Sperm whale
Dolphin
Baleen whales - mysticetes
Humpback whale
Blue whale
Gray whale
Convert evolution with fish
Convergent evolution- independent development
of similar features because of adapting/
evolving in similar habitats
• Flukes - like vertical tail fins but turned 90%
• Killer whales and dolphin dorsal fin, triangular
like sharks
• Hair- lost
• Breathing- valve close blowhole
Porpoise Embryo
Embryo has : 4 limbs buds
Pelvis
Tail
Nostrils toward front of head
During Development:
1. Forelimb buds become flippers
2. Rear limb buds fail to mature - remain within body of
adult
3. Nostrils shift from snout to top of head= blowhole
4. Flipper- bone structure similar to terrestrial
ancestors. Fingers are attached to arm bones and
wrist bones
5. Even baleen whales have embryonic tooth buds
So…Evidence from:
1)
2)
3)
4)
Fossils- Paleontologists
DNA- molecular Biologists
Embryology- embryologists
Comparative anatomy- zoologists
homologous structures
vistigual organs/structures