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NOTES: Whale Evolution

NOTES: Whale Evolution. Defining Characteristics of Mammals:. Body covered in hair/fur Young nourished with milk from the mother (mammary glands) A 4-chambered heart in a closed circulatory system A diaphragm that separates the thoracic (chest) cavity from abdominal cavity

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NOTES: Whale Evolution

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  1. NOTES: Whale Evolution

  2. Defining Characteristics of Mammals: • Body covered in hair/fur • Young nourishedwithmilk from the mother (mammary glands) • A 4-chambered heart in a closed circulatory system • A diaphragm that separates the thoracic (chest) cavity from abdominal cavity • Are warm-blooded; maintain stable internal temperature

  3. The Story of Whale Evolution Question: How did whales get here?Hypothesis: Whales evolved from terrestrial mammals, with modifications in their anatomy and physiology selected for in a changing environment. Evidence needed? Fossil remains of whale-like mammals, with limbs of varying degrees of reduction and other features varying in similarity to modern whales.

  4. Modern Cetaceans Odontocetes (toothed whales): -clearly aquatic -teeth -one blowhole Earliest evidence of these modern whales in the fossil record? ~30 mya

  5. Modern Cetaceans Mysticetes (baleen whales): -clearly aquatic -baleen plates (teeth present only in embryonic development) -two blowholes Earliest evidence of these modern whales in the fossil record? ~29 mya

  6. EVIDENCE #1: The Fossil Record • Scientists have found a lot of whale-like fossils in Pakistan that date to the Eocene epoch (55 mya – 34 mya). WHY?

  7. Between the landmass we call “India” and the mainland (Asia) was the Tethys Sea. • Continental drift pushed India into Asia, forming the Himalayan Mts (& Mt Everest!), eliminating this part of the Tethys Sea (and pushing the ocean floor to the top of a mountain chain – including its fossils!)

  8. The movement of India into Asia caused the Tethys Sea to become shallower and saltier – creating a rich food supply for organisms to take advantage of. • This changing environment presented a new opportunity for those who could take advantage of it (i.e. those with adaptations for feeding in the marine environment).

  9. Eocene Epoch TimelineLet’s rediscover the fossil evidence, as the scientists did – following the sequence of discovery (NOT chronological order).Keep in mind the EXCITEMENTthat paleontologists must have felt, as they found evidence of organisms with predictable intermediate traits (“transitional forms”) between land mammals and today’s modern whales.

  10. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic

  11. DORUDON, 36 mya (1936) • Clearly aquatic • Primitive whale: distinctive teeth, reduced hind limbs

  12. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic Pachyaena55 mya (1955) clearly terrestrial

  13. PACHYAENA, 55 mya (1955) • Clearly terrestrial • Land mammal: same distinctive teeth, tiny hooves

  14. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic Pakicetus50 mya (1983) clearly terrestrial Pachyaena55 mya (1955) clearly terrestrial

  15. PAKICETUS, 50 mya (1983) • Clearly terrestrial • Land mammal: same distinctive teeth and tiny hooves, but distinct whale-like ear region -Group Creodonts, wolf-sized carnivores -Found to have a lower % 18O in teeth / bones; evidence of a freshwater environment

  16. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic Basilosaurus37 mya (1990)clearly aquatic Pakicetus50 mya (1983)clearly terrestrial Pachyaena55 mya (1955)clearly terrestrial

  17. BASILOSAURUS, 37 mya (1990) • Clearly aquatic • Primitive whale: same distinctive teeth, but reduced hind limbs and flippers

  18. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic Basilosaurus37 mya (1990)clearly aquatic Rodhocetus46 mya(1994)clearly aquatic Pakicetus50 mya (1983)clearly terrestrial Pachyaena55 mya (1955)clearly terrestrial

  19. RODHOCETUS, 46 mya (1994) • Clearly aquatic • Primitive whale: same distinctive teeth, tiny hooves, whale-like ear region, PLUS hind limbs disengaged from pelvis, nostrils further back on head, less flexible neck -Shorter front limbs and hind limbs disengaged from pelvis BOTH indicate an aquatic habitat

  20. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic Basilosaurus37 mya (1990)clearly aquatic Need evidence of a “transitional form” from wolf-sized carnivore to whale! Rodhocetus46 mya(1994)clearly aquatic Pakicetus50 mya (1983)clearly terrestrial Pachyaena55 mya (1955)clearly terrestrial

  21. AMBULOCETUS, 48 mya (1994) • A TRANSITIONAL FORM! • “The Walking Whale”: front limbs with fingers and tiny hooves, hind limbs clearly adapted for swimming, whale-like ear region -This organism would have walked on land like a sea lion, but swam like a sea otter

  22. Eocene Epoch Timeline Dorudon36 mya (1936) clearly aquatic Basilosaurus37 mya (1990)clearly aquatic Rodhocetus46 mya(1994)clearly aquatic Ambulocetus48 mya (1994)transitional form! Pakicetus50 mya (1983)clearly terrestrial Pachyaena55 mya (1955)clearly terrestrial

  23. Ambulocetus

  24. Whales’ Closest Living Relative?

  25. Whales’ Closest Living Relative? • Pachyaena (the terrestrial ancestor lineage) is EXTINCT • So, who are the closest living relativesof whales? • Maybe Hooved Mammals: Ungulates? • -Perissodactyls(odd-toed) • -Artiodactyls (even-toed)

  26. PERISSODACTYLS (odd-toed ungulates) Horses & Zebras Rhinos & Tapirs

  27. ARTIODACTYLS (even-toed ungulates)

  28. EVIDENCE #2: Anatomical Evidence • Early whale ankle bones have two smaller ridges, indicating a closer relationship with artiodactyls • Mesonychid ankles (the extinct lineage) have one large ridge, indicating they are more closely related to perissodactyls Pakicetus Artiodactyls Pachyaena Perissodactyls

  29. EVIDENCE #3: Molecular Evidence • Scientists can also compare the DNA of whales with that of artiodactyls. • For example, scientists can compare segments of the beta-casein gene (a gene that codes for the production of milk protein), which is found in all mammals:

  30. EVIDENCE #3: Molecular Evidence • 2 porpoise & sperm whale • 3 porpoise & right whale • 3 sperm whale & right whale • 3 sperm whale & hippo • 3 porpoise & hippo • 3 right whale & hippo • 3 giraffe & deer • 3 giraffe & cow • 4 cow & deer 2-3 differences, comparing DNA among whales 3 differences, comparing DNA between whales & hippos 3-4 differences, comparing DNA among artiodactyls

  31. RECAP – Evidence for Whale Evolution • Distinctive teeth link whales to the 4-legged, terrestrial Mesonychids(Pachyaena)of the Eocene epoch. • Tiny hooves on Mesonychids and early whale toes tie whales to the Ungulates • Similar ankle bones(with 2 ridges) link early whalesto Artiodactylsas the closest relatives of whales

  32. RECAP – Evidence for Whale Evolution • DNA similarities confirm the artiodactyl connection and points to hippos as the closest cousins of whales! • These multiple, independent lines of evidence strengthen, narrow and confirm the hypothesized relationship between whales and artiodactyls

  33. Whales’ Closest Cousin? Hippos!!

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