Before the dinosaurs, it's thought there were mammal like reptiles living on the Earth. What was so mammalian about them?

Fossil remains of the reptiles that were around before the dinosaurs, shows that their teeth were differentiated. The teeth of reptiles today are all the same: they are all pointed. The reptiles that lived before the dinosaurs had teeth designed for different purposes. Like us, they had molars for grinding their food and canines and incisors for ripping their food apart.