Before the Jurassic period, the great age of the dinosaurs, we find the Triassic, not as well known but very interesting events. In this period when the continents are separated from Pangea, facilitating new diversity of different species. During the Triassic mammal-like reptiles disappeared or mammal-like reptiles ... a type of animal that are midway between mammals and reptiles, and it was late in the period when the first dinosaurs dinosaurs (again because it gives me the wins).
An example of these reptiles mamiferoides disappeared are cynodonts. The cynodont is a missing link between reptiles and mammals, in fact, its name literally means "dog teeth" and if we saw it, we remind some kind of dachshund with a little alopecia. It is an animal that does not exceed one meter in length, with a small, thick tail of about 30 cm. It fed on insects and small reptiles.
When it ran, its back was moving from side to side like a lizard running (just imagine a komodo dragon running); but its body has hair and live in burrows with his beloved spouse, like mammals.
Another feature of this prehistoric animal and half mammal, half reptile, is the offspring. The couple lived cynodont within a burrow, and inside this put the eggs were hatching, like most reptiles. However, when pups out breaking the shell, they were totally dependent on their parents. For example we see that existing crocodiles out of the burrow and are adults but reduced, however, the size of most mammals are born and take time to break away from the mother because they are dependent and need to develop a strategy is more ... survival differently. Well so do the cynodonts, pup birth three months are left sucking the milk from the glands of the mother and not leave the den until they are developed enough. This is a clever way that the offspring is not threatened by predators that may have the outside world.
How I love the picture above, it is as if it were a super-predator, dangerous and totally unscrupulous murderer mammiform. But let's face it, maybe it was like in the image below.
The importance of these mammal-like reptiles, is that these small mammals evolve and hairy (the size of mice or squirrels), since dinosaurs were the kings of the food chain for 160 million years. You and I probably have in our genes the essence of cynodonts.