Scales, eggshells, and a beating heart

Evolution continues

The small reptile Petrolacosaurus possessed three significant evolutionary advantages over amphibians, which were, up to this point, the dominant life form. Petrolacosaurus was therefore significantly better adapted to life on land.

First of all, unlike the amphibians, it did not have to keep its skin constantly moist. The reason for this was an evolutionary innovation: scales. Scales offer protection, are more flexible than a shell and injuries heal faster than on uncovered skin. To this day, all reptiles have scales, and the skin of the giant dinosaurs was also covered with scales.

In addition, the reptiles began to develop hard eggshells. This meant they no longer had to return to water to reproduce, or even live near water. On the contrary, they could cover long distance and this way conquered every corner of the planet.

The eggs of Petrolacosaurus were large, the shell protected the embryo inside. But since the embryo also absorbed air through the shell, it died as soon as the egg was covered with water. It is therefore assumed that Petrolacosaurus built its nests in higher hiding places. This way they were not only safe from flooding, but also from amphibians and insects.

But the greatest advantage Petrolacosaurus possessed over all other creatures of its time was its unusually powerful heart. A heart, fossilised finds have shown, was already very similar to the hearts of today's birds and mammals. 

For despite all evolutionary progress, Petrolacosaurus was only a small reptile in the midst of a world of giant insects and amphibians, an animal that was preyed upon, at the bottom of the food chain. So, it sought its salvation in flight and developed a highly efficient heart to do so. It is thanks to the tiny reptile Petrolacosaurus that the prototype of what is probably the most important muscle in our body was already developed in the carboniferous period.