Birds evolved from
a. insects.
b. a common ancestor with reptiles.
c. amphibians.
d. mammals.

B

Explanation:

The evolution of birds is yet to be fully ascertained and this is due to the fragility of bird bones, as they do not fossilize as well as other vertebrates. Recently discovered fossils from China, South America and other countries made the discovery that birds evolved from small carnivorous dinosaurs possible.

For decades, the fossil link between birds and dinosaurs was Archaeopteryx. Archaeopteryx is from the Jurassic period and was the first known bird. In the 1860's, it became a specimen in search for the ancestors of living birds. Archaeopteryx had feathers along its arms and tails just like living birds but it had teeth and and a bony tail, which is not a characteristics of living birds. Also, the skeletal structure in Archaeopteryx were distinct from that of living birds. Due to this characteristics, Archaeopteryx was recognized as an intermediate between birds and reptiles i.e. it has characteristics of both dinosaurs and birds.

Birds are diapsids i.e. they have two openings in their skulls. Birds belong to a group of diapsids called archosaurs, which also includes crocodiles and dinosaurs. Dinosaurs are divided into two groups Saurischia (lizard-like) and the Ornithischia (bird-like). The Saurischians is further divided into two groups, in which bipedal predators called THEROPODS is one of them.

In 1970's, paleontologists discovered based on fossils of Archaeopteryx that it shared unique features with small carnivorous dinosaurs called THEROPODS. Based on the shared characteristics between the fossils of theropods and birds (hip and wrist bone inclusive), it was suggested by scientists that maybe the theropods are the ancestors of birds.

correct answer is option a.

tropopause, stratopause and mesopause have all in common aspect that is point of maximum temperature in its layer of the atmosphere. all layers of atmosphere observe abrupt change in temperature. tropopause is the boundary between troposphere and stratosphere. stratopause is the boundary between stratosphere and mesosphere. mesopause is the boundary between mesosphere and thermosphere. these all boundaries are ranges between altitude of 0 to 80 km.