Previous Year Question
Consider the following events:
First reptiles
First insects
Shelled animals
First mammals
Arrange the above events in Chronological order of their origin on the earth and select the correct answer from the codes given below:
2, 1, 3, 4
2, 3, 1, 4
3, 2, 1, 4
2, 4, 1, 3
Correct Answer: C
Detailed Solution
The correct chronological order is—Shelled animals → First insects → First reptiles → First mammals.
Early hard-shelled animals appeared very early in the history of marine life. Some shell-bearing organisms were already present by the end of the Ediacaran, while during the Cambrian Period, about 541 million years ago, shells and other hard body parts became much more common among animals.
Insects appeared later in the fossil record. The oldest known insect fossils are associated with the Devonian Period, which means insects had evolved before reptiles and mammals.
The first reptiles appeared about 300 million years ago, during the Late Carboniferous/Pennsylvanian. The evolution of the amniotic egg was an important step in this transition because it reduced the dependence of vertebrate reproduction on water.
Mammals evolved still later during the Triassic Period. Early mammals were small and lived alongside dinosaurs and other reptiles.