When did first true mammals appear?

The earliest known mammals were the morganucodontids, tiny shrew-size creatures that lived in the shadows of the dinosaurs 210 million years ago. They were one of several different mammal lineages that emerged around that time.

Read, more on it here. Also to know is, when did mammals first appear on Earth?

about 200 million years ago

Subsequently, question is, did mammals or dinosaurs come first? Mammals first appeared at least 178 million years ago, and scampered amid the dinosaurs until the majority of those beasts, with the exception of the birds, were wiped out 66 million years ago. But mammals didn't have to wait for that extinction to diversify into many forms and species.

In respect to this, where did the first mammals come from?

Mammals evolved from a group of reptiles called the synapsids. These reptiles arose during the Pennsylvanian Period (310 to 275 million years ago). A branch of the synapsids called the therapsids appeared by the middle of the Permian Period (275 to 225 million years ago).

How did early mammals survive during the age of dinosaurs?

It was their diet which enabled these mammals to survive in habitats nearly devoid of plant life. Mammals, in contrast, could eat insects and aquatic plants, which were relatively abundant after the meteor strike. As the remaining dinosaurs died off, mammals began to flourish.