LIFE SCIENCE

Detailed explanation-1: -Pharyngeal pouches develop in the early embryos of all vertebrates, including the air-breathing terrestrial reptiles, birds, and mammals. The number of pouches has been reduced in the course of evolution from six or more to four in tetrapods, and the posterior pouches may not actually break through.

Detailed explanation-2: -The resulting pouches give rise to the middle ear cavity, Eustachian tube, mastoid air cells, palatine tonsils, thymus, parathyroid, and parafollicular cells of the thyroid.

Detailed explanation-3: -Amphibians, reptiles, mammals, and birds evolved after fish. The first amphibians evolved from a lobe-finned fish ancestor about 365 million years ago. They were the first vertebrates to live on land, but they had to return to water to reproduce. This meant they had to live near bodies of water.

Detailed explanation-4: -But the underlying similarities of these homologous bones reveal that all these animals share a common ancestor: a four-legged animal–a tetrapod–living over 365 million years ago. This cladogram shows the common ancestor of modern vertebrates, why they are similar, and indicates points of divergence through time.