Reptile's Beginnings

The Carboniferous was the time when first giant land plants evolved: ferns, horsetails, lycopsids, etc. These plants were giant and green, but they weren't related to modern trees, shrubs and grasses, as they reproduced with spores (similar to the fungi) and required plenty of heat and moisture to thrive (i.e. the Carboniferous climate). They released plenty of moisture and oxygen into Earth's atmosphere at that time, making Earth prone to sudden and devastating fires as well.

The Carboniferous was a time of giant invertebrates and the heyday of amphibians; the first reptiles, featured by Hylonomous and Petrolacosaurus already had a number of important evolutionary advantages: water-proof eggs for the young and scaly skin for the adults and an efficient heart, but their small size still made them vulnerable to such predators as the giant Mesothelae spider.