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Clash of Titans
Late Carboniferous (300 MYA)Edit
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.
WWM's segment on Carboniferous featured Meganeura, a giant dragonfly, and Arthropleura, a distant cousin to modern millipedes and centipedes. Like the Mesothelae, these invertebrates were true giants, having reached such size due to the overabundance of oxygen in the atmosphere.
Proterogyrinus was another animal featured in this segment: it was an amphibian that belonged to the branch that had evolved into reptiles. Adult Proterogyrinus had many reptile-like features and was a very successful animal; however, when the Carboniferous world of giant insects and spiders came to an end, so did the world of the amphibians.
Early Permian (280 MYA)Edit
The early Permian segment of Reptile's Beginnings featured early mammal-like reptiles: Dimetrodon and Edaphosaurus, the sail-backed reptiles. These sails were very efficient heating and cooling devices, able to catch the warming sun rays and the cooling breezes, but the sail-backed reptiles were just side branches of reptiles to mammal evolution.
By the beginning of the Permian, Earth came through another Ice Age (not featured in WWM), and as a result, the planet's climate was much more continental and drier than in the previous Carboniferous. The earlier plants, like the giant horsetails and ferns largely died-out (though some of them would recover by the Mesozoic Era), replaced by Earth's first conifers, which emitted less moisture and oxygen into the atmosphere and kept more of the plants themselves.
Consequently, Earth's insects and other invertebrates shrank in size and were no longer dangerous to the vertebrates. The amphibians, with their thin skin and dependance on water too shrank in size (i.e. Seymouria from this episode) and by the second half of the Permian, when most of Earth's landmass became a desert, they died out. But the reptiles, including mammal-like reptiles, but not the sailbacks, thrived, and were ready to take over the world...