As time passed into the Jurassic period, Pangaea started to break apart. Rifts opened between what became Africa, South America, and North America. New ocean basins started to form. As the continents separated, coastlines grew longer. Shallow seas spread over continental margins. These seas supported abundant marine life.The breakup of Pangaea changed climate patterns. Ocean currents reshaped heat transport around the globe. Regional climates became more varied. Some areas grew wetter, supporting dense forests. Others stayed semi arid but experienced more complex patterns of rainfall. Environments diversified as plate boundaries migrated.By the Cretaceous period, the continents looked more familiar. North America and Eurasia had partial separation. South America, Africa, India, Antarctica, and Australia drifted apart. Large inland seaways flooded parts of continents. In North America, a broad interior sea split the land into two long islands. Warm global climate and high sea level produced extensive shorelines and shallow marine habitats.Across these changing continents, vegetation also transformed. Early in the Triassic, many forests contained seed ferns and strange extinct plant groups. Conifers already existed but had not yet become completely dominant. Over time, conifers took over many upland and mid latitude forests. These conifers were ancestors or relatives of modern pines, cypresses, and araucarias. Ginkgo trees populated some temperate regions. Cycads and related plants filled warm lowlands.Cycads resembled short stout palms with crowns of tough leaves. They thrived in subtropical and tropical zones. Bennettitales, another extinct group, looked somewhat similar and shared those environments. Ferns carpeted forest floors and riverbanks. Horsetails lined wetlands and lake margins. Together, these plants formed the backdrop for early dinosaur ecosystems.Most early dinosaurs were modest sized animals moving through such plant communities. Small bipedal herbivores nibbled low vegetation. Carnivorous species preyed upon them and upon other reptiles. Herbivorous dinosaurs needed large volumes of plant material. Their digestive systems evolved to process tough, fibrous leaves and stems. Because trunks and leaves of Mesozoic plants were often nutrient poor, many herbivores ate almost constantly.During the Jurassic period, conifer forests reached great heights. Towering araucaria like trees created tall canopies. Underneath grew cycads, ginkgos, seed ferns, and many ferns. Sauropod dinosaurs, the giant long necked herbivores, roamed these forests and floodplains. Their long necks allowed them to feed from several levels of vegetation without moving their huge bodies far. Some species likely swept broad feeding paths through canopies.Different dinosaur herbivores specialized on different plant types. Stegosaurs, with their small heads and beaklike mouths, probably focused on low shrubs and ground plants. Ornithopods, including early relatives of duck billed dinosaurs, handled medium height vegetation. Massive sauropods targeted high branches and tall conifers. This separation in feeding height reduced direct competition for food. It allowed many large herbivore species to share the same landscapes.In the Cretaceous period, a major change reshaped plant communities. Flowering plants, called angiosperms, began to appear and then diversify. At first they occupied limited habitats like riverbanks and disturbed soils. Over tens of millions of years, they spread into more environments. Flowering plants offered new types of leaves, seeds, and fruits. They often grew faster than conifers and cycads. They tolerated disturbance and adapted to varying conditions.As flowering plants expanded, some dinosaur groups adapted alongside them. Many small herbivorous dinosaurs developed more complex teeth. Their jaws allowed thorough chewing of tough plant material. Duck billed dinosaurs, or hadrosaurs, evolved intricate dental batteries. These acted like grinding mills for foliage. Horned dinosaurs developed powerful jaws and shearing beaks. Together with hadrosaurs, they formed large herds in Cretaceous floodplains and coastal lowlands.By late Cretaceous times, landscapes in many regions looked like patchworks. Conifer forests persisted in some uplands and higher latitudes. Mixed forests of conifers and flowering plants filled mid latitudes. Lowland plains and river valleys hosted diverse flowering shrubs, trees, and ground plants. Fern prairies spread after disturbances such as volcanic eruptions or local floods. Dinosaurs moved through this mosaic, browsing and grazing in different patches.While dinosaurs dominated the land, other reptiles ruled the skies and seas. Pterosaurs were the flying reptiles of the Mesozoic. They were not dinosaurs, though closely related to them. Early pterosaurs appeared in the Late Triassic period. Over time they developed impressive variety in size and lifestyle. Some species had wingspans similar to modern gulls. Others reached spans larger than a small aircraft.Pterosaur wings formed from membranes of skin and muscle. These membranes stretched from the elongated fourth finger of each hand down to the body and legs. Their skeletons were lightweight and filled with air spaces. This construction reduced body mass while maintaining strength. Many pterosaurs possessed long jaws lined with teeth suited to catching fish or small animals. Later forms included toothless beaked species that may have scavenged or probed for food.The sky during much of the Mesozoic carried numerous pterosaurs above the land and sea. Some soared over oceans, snatching fish from near the surface. Others flew along coastlines, estuaries, and river valleys. Inland species may have hunted small vertebrates or large insects. Their presence added another predatory layer above terrestrial dinosaurs and marine reptiles.At sea, several distinct groups of marine reptiles flourished. Ichthyosaurs resembled streamlined dolphins with vertical tail fins. They were not mammals but reptiles fully adapted to marine life. Their bodies allowed fast sustained swimming. Many preyed on fish and cephalopods such as ammonites. Fossil stomach contents confirm these diets. Large eyes suggest some ichthyosaurs hunted in low light or deeper waters.Plesiosaurs formed another major group of marine reptiles. They had broad bodies, four strong flippers, and relatively short tails. Within plesiosaurs, two general forms emerged. Long necked plesiosaurs had small heads and many neck vertebrae. They likely used flexible necks to sweep through schools of fish or to ambush prey from below. Short necked pliosaurs carried massive skulls and strong jaws. They functioned as top predators, attacking large fish and other marine reptiles.Mosasaurs entered the seas during the Cretaceous period. They were related to lizards and snakes rather than to earlier marine reptiles. Mosasaurs had long bodies and powerful tails used for propulsion. Their jaws contained sharp conical teeth. Many species also had pterygoid teeth along the palate, helping grip slippery prey. Mosasaurs hunted fish, turtles, ammonites, and even other mosasaurs.These marine reptiles shared their oceans with many invertebrates and fish. Coral reefs and sponge communities built complex habitats. Ammonites and belemnites, relatives of modern squid, filled open waters. Shoals of bony fish and sharks moved through coastal and offshore zones. Plankton blooms in warm shallow seas fueled this productivity. The breakup of Pangaea created more continental shelf areas, which favored these rich marine ecosystems.
