1.9: Jurassic Park- World of Reptiles
The climate on Earth in this epoch (Jurassic and Early Cretaceous) approached the optimum, the split of the continental plates led to its humidification. A new flourishing of fauna and flora began. The sea strongly prevailed over the land, even high continental platforms such as the Russian and North African, were flooded.
The abundance of phytoplankton and zooplankton caused the thrive of marine fauna, including sponges, corals, bivalve mollusks (who took an active part in the construction of bioherms), echinoderms, etc. Ichthyosaurs and plesiosaurs were the most abundant marine predators.
Interestingly that in fossil deposits, pregnant females of ichthyosaurs are often found. Therefore, the ichthyosaurs were not only viviparous but also gave birth in conditions that “promoted” fossilization. The reason is they likely could not give birth as modern cetaceans: a tail up, this was not allowed with their vertical (like in fish, but not like in cetaceans) caudal fin. Then it seems that they were forced to give birth in shallow water, probably forming large groups (like modern seals).
On land, there were forests similar to the recent temperate taiga, composed mainly of representatives of the ginkgo class. Many of them were technically also angiosperms as their seeds were well protected by additional covers. These forests were mostly inhabited by insects, and primitive mammals hunted for them.
In open spaces, savanna forests were maintained (as modern grasslands exist only due to the constant pressure of ungulates) by giant herbivorous dinosaurs, replacing all the other groups with size of a modern cow and bigger. There also lived numerous predatory dinosaurs, both large and small bird-like insectivorous forms.
Flight of ancient birds was still very imperfect. The ancestors of birds needed feathers mainly for thermal insulation, and the flight occurred from the jumping movements required to catch flying insects. There is no much difference between archosauromorph reptiles and birds; in fact, flying is the only radical difference of birds.
The other group of flying archosaurs, pterosaurs, dominated the water and land borders. Ancestors of pterosaurs were fish-eating animals, and their flight arose as an adaptation to catching prey from the water.