question archive Discuss whale relative size of each ancestor, terrestrial or aquatic, and major anatomical changes
Discuss whale relative size of each ancestor, terrestrial or aquatic, and major anatomical changes
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Discuss whale relative size of each ancestor, terrestrial or aquatic, and major anatomical changes.
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- Pakicetus, is thought to be the "first cetacean" who roamed the land. It is a quadruped which measures around 1 - 2 meters long. Based on fossil records found in Pakistan, its skeleton has revealed that it had a typical cetacean skull and artiodactyl ankles (even-toed ungulates). Due to this, it was assumed that it was a terrestrial species who roamed the land 50 million years ago, as evident to its ankles which shows running ability. Even though it was a terrestrial mammal, it was considered as cetacean because of its inner ear morphology. Its teeth's shape revealed that it was a carnivorous land mammal.
- Indohyus, considered as the closest distant ancestor of whales (80 cm in length). The ability to thrive in aquatic environment is driven by their inept ability to escape predators. However, many dismissed this claim as they believed that the ancestor is more of an omnivore than a herbivore. Meanwhile, Ambulocetus were a four-legged while with webbed legs to aide for swimming and walking. Several analysis showed that it could have thrived in both marine and freshwater habitats, while its inner ear morphology indicates that it is an aquatic species.
- 34 million years ago, the ancestor of the modern whale probably lacked baleen and could not use echolocation. Due to the increasing changes in the ocean ecosystem, 5 million years after, they evolved and diversified. These era was marked by the increase morphological changes such as increase in size (5 to 9 meters in length) to favor strong selection pressure as ocean temperature drops. Other changes include hind limbs that disappeared and front limbs that transformed into fins. The body has lost its fur and nearly all of its hair. It is streamlined. A horizontal, powerful propeller of a tail has attached itself to the vertebral column.
