Those who have studied animals say that mammals had started to emerge when they separated from reptiles and birds. There was a time when mammals have similar characteristics to these two types of families. The first mammals may have formed during the early Jurassic period. Some say that the first real mammal is known as the skinny shrew.
This started to live even before the dinosaurs started. Their main goal is to get insects from the ferns that can be found in shores so that they would have something to eat. They lived over 160 million years ago. This mammal may have evolved after the dinosaurs started to appear.
Mammals have evolved over millions of years. It is believed that mammals originated from SYNAPSIDS. Synapsids diverged from the main reptile stock. Synapsids are known to be heavy-bodied, stumpy legged creatures with a large head. Over time, the Synapsids adapted to various types of habitats and food. Some of them were insect eaters, and some others were rodent-like seed-eaters.
Synapsids arose during the Pennsylvanian Period about 310 to 275 million years ago. A particular branch of the synapsids known as the “therapsids” is believed to have appeared around the middle of the Permian Period, which was about 275 to 225 million years ago. Millions of years later, some of these therapsids evolve many of their features that would later be associated with mammals.