Zoology 10th Edition by Stephen Miller,John Harley

تمرين 9

Mammals are characterized by the presence of mammary glands; hair; a diaphragm; three middle-ear ossicles; sweat, sebaceous, and scent glands; a four-chambered heart; and a large cerebral cortex. They evolved in the synapsid amniote lineage, which has been traced back about 320 million years. The ancestors of modern mammals survived two mass-extinction events, 240 and 65 mya. The demise of the dinosaurs in the last extinction event allowed surviving mammals to diversify into niches formerly occupied by the dinosaurs. The beginning of the Tertiary period marks the beginning of the "age of mammals."
In what ways did the demise of the dinosaurs present evolutionary opportunities for mammals? What evidence of their early evolution is seen in modern mammals?