In your OWN words, describe the cardiac cycle

The cardiac cycle is defined as a sequence of alternating contraction and relaxation of the atria and ventricles in order to pump blood throughout the body. ... In other words, when the atria are in diastole, the ventricles are in systole and vice versa.The cardiac cycle describes all the activities of the heart through one complete heartbeat—that is, through one contraction and relaxation of both the atria and ventricles. ... The volume of the ventricles remains unchanged (isovolumetric) during this period.

Explanation:

a. small and rodent-like

Explanation:

During the Mesozoic the first mammals appear, they lived with the dinosaurs and managed to survive the meteorite, the scientists explain that the underground burrows and the aquatic environments where the first mammals were hiding from the dinosaurs also managed to protect them from the rising temperatures, this  was thanks to theirs small size. According to paleontological studies it is known that the organization of mammals remained in the form of almost always insectivorous and small-sized animals, arboreal and nocturnal.