Answer :
Final answer:
The evolution of mammals began with their predecessors, the synapsids, around 300 million years ago, transitioning through therapsids, and leading to early mammals in the Jurassic period.
The rise of monotremes, marsupials, and placentals was significant in mammalian diversification, marked by the development of a placenta (excluding monotremes), milk for offspring, and the maintenance of constant body temperature.
Explanation:
Evolution of Mammals
The evolution of mammals can be traced back to their ancestors, the synapsids, which emerged close to 300 million years ago.
The evolutionary path led from synapsids to therapsids and to the first known mammals in the early Jurassic period, approximately 205 million years ago. A significant fraction of this mammalian diversification occurred from the Jurassic to the Cretaceous periods, with the advent of small, gliding mammals and the rise of monotreme, marsupial, and placental mammals.
The evolution of mammals is marked by several key developments:
Placental development (except in monotremes like the platypus and echidna)
Care for newborns through maternal nurturing and milk from mammary glands
Maintenance of constant body temperature independently of the environment
Key events in mammalian evolution are arranged chronologically below:
Emergence of synapsids (~300 mya)
Evolution from synapsids to therapsids
First known mammals (205 mya)
Dividing line for monotremes, marsupials, and placentals evolution
Diversification of mammals in the Cenozoic era (post-dinosaur extinction, ~65 mya)
