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Evolution of Cetaceans: Whales and Hippos Connection Explored

Explore the evolutionary journey of cetaceans using DNA evidence, fossil findings, and embryological studies to uncover the link between whales and hippos. Learn about ancestral species like Pakicetus and Ambulocetus, and discover the convergent evolution of modern cetaceans.

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Evolution of Cetaceans: Whales and Hippos Connection Explored

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  1. Cetacean Evolution

  2. 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?

  3. 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

  4. 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

  5. 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

  6. Basiloaurus Toothed whales - odontocetes • Killer whale • Sperm whale • Dolphin Baleen whales - mysticetes • Humpback whale • Blue whale • Gray whale

  7. 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

  8. Porpoise Embryo Embryo has : 4 limbs buds Pelvis Tail Nostrils toward front of head During Development: • Forelimb buds become flippers • Rear limb buds fail to mature - remain within body of adult • Nostrils shift from snout to top of head= blowhole • Flipper- bone structure similar to terrestrial ancestors. Fingers are attached to arm bones and wrist bones • Even baleen whales have embryonic tooth buds

  9. So…Evidence from: • Fossils- Paleontologists • DNA- molecular Biologists • Embryology- embryologists • Comparative anatomy- zoologists homologous structures vistigual organs/structures

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