Petrolacosaurus was a primitive diapsid lizard reptile. It was also the very first and earliest reptile ever to evolve.
Petrolacosaurus lived during the Carboniferous peiord, sharing its environment with the giants insects and amphibians is lived alongside with.
Petrolacosaurus was small and looked similar to modern lizards. Although it was very small, Petrolacosaurus often hunted smaller insects on the forest floors of the Carboniferous, but the creature itself was fairly low on the food chain.
Unlike amphibians, Petrolacosaurus, like all reptiles, had tough, scaly skin which trapped moisture inside their bodies, vital for all land dwellers. Because they didn't dry out in the sun, they could venture away from water. They also had evolved a complex heart, which was much more efficient than their enemies. In fact, their hearts were the templates for our own. In the case of Petrolacosaurus, it was a powerful pump that pushed blood and oxygen around their bodies to their muscles so they could run at high speeds without stopping for a rest.
Petrolacosaurus may have often spent time in wholes, but they didn’t need burrows to avoid danger, they had speed and stamina on their side.