Question

Please answer the following related to the concept of evolution:

A. What are three characteristics of the skeletons of vertebrate animals (such as a dog, cat, horse, or primate) that suggest they represent homologous structures? What is a homologous structure?

B. Why do the fossils of whales and their ancestors support the idea that whales evolved from a four-legged terrestrial vertebrate mammal?

Answer 1

Homologous structures

Homologous structures are structures like bones or organs in different organisms having anatomical similarity with each other. These structures have similar anatomical features which indicates that different organisms would have a common ancestor. Homologous structures are structurally similar, this does not mean they must have identical shapes or functions.

Three characteristics of the skeletons of vertebrate animals (such as a dog, cat, horse, or primate)

1. The forelimbs of vertebrate show homologies. The Pentadactyl is common in all vertebrates, but they perform different function

2. The pelvis of vertebrates (a dog, human, cats and even snake) are similar in structures.

3. The tailbone in human beings is also considered as a homologous structure and is shared by most of the vertebrate animals

B) The fossils of whales and their ancestors support the idea that whales evolved from a four-legged terrestrial vertebrate mammal because the first fossil evidence to be discovered was of Pakicetus, which was a land animal with four well-functioning legs. They consist of long skulls and the regions of ear supported by bony wall are exclusively found in today’s living whales. The presence a large auditory bulla in the inner ear formed from ectotympanic bone found in cetaceans (order of aquatic mammals like whales, dolphins etc) provided the evidence that whale had evolved from four-legged mammal.