Question

what do you mean by the terms given below :
( i ) Cretaceous era
( ii ) Jurassic era
( iii ) Permian era
( iv ) Triassic era
And also which - which organisms takes place evolution in these era ?

Answer 1

The Mesozoic era (age of reptiles) is divided into three periods namely Cretaceous (135 million years), Jurassic (180 million years), and Triassic (225 million years). The era before the Mesozoic is called Paleozoic which is divided into the following periods - Permian (275 million years), Carboniferous (345 million years), Devonian (395 million years), Silurian ( 430 million years), Ordovician (500 million years), and Cambrian (600 million years).
1. Cretaceous period - During this period appeared the archaic eutharian mammals, modern birds and teleost fishes. Toothed birds and giant reptiles were extinct. The number of gymnosperms were slowly reducing and the angiosperms were increasing in number.
2. Jurassic period - The dominant organisms were the giant dinosaurs, toothed birds, and among plants the gymnosperms were widely spread.
3. Triassic period - The dinosaurs first appeared during this period. Primitive amphibians were slowly becoming extinct. Gymnosperms were abundant.
4. Permian period - During this period there was abundance of primitive reptiles, decline of amphibians, many marine invertebrates became extinct, modern insects first appeared.