The Age of Reptiles

By: Rhiannon Shiloh

Summary of The Age of Reptiles: In the beginning of the Triassic, the continents were in the Pangaea formation. Weather was hot and dry then cold in the winters, causing a lot of deserts. Grasshoppers were introduced, plants and insects didn't go through many changes during this time. The first mammals evolved near the end of this period, they were very small and mainly herbivores or insectivores. Next came the Jurassic period, during this time, Pangaea began to split apart into two pieces. The temperature was was warm and this caused diversity among reptiles. Plants evolved to have roots and use spores to reproduce. Reptiles were dominant in this time, though by the end of it, giant sauropods were starting to go extinct. Mammals remained small and of no competition to larger animals. Marine life was diverse. Last in the Mesozoic Era was the Cretaceous Period. During this time, Pangaea continued to drift apart. Towards the end of the period, the continents were closer to their current placement. Ocean levels were high and a lot of the land we know today was underwater. Flowering plants developed during this time.

How long did it last?:
Age of Reptiles = 286-65 MYA

What did the continents look like/what was going on on Earth/what was life like?:
Triassic: most of the continents were concentrated in the giant C-shaped supercontinent known as Pangaea. Climate was generally very dry over much of Pangaea with very hot summers and cold winters in the continental interior. The oceans had been massively depopulated by the Permian Extinction when as many as 95 percent of extant marine genera were wiped out by high carbon dioxide levels. Plants and insects did not go through any extensive evolutionary advances during the Triassic. Due to the dry climate, the interior of Pangaea was mostly desert. In higher latitudes, gymnosperms survived and conifer forests began to recover from the Permian Extinction. Mosses and ferns survived in external image lb_icon1.png regions. Spiders, scorpions, millipedes and centipedes survived, as well as the newer groups of beetles. The only new insect group of the Triassic was the grasshoppers.The Mesozoic Era is often known as the Age of Reptiles. Two groups of animals survived the Permian Extinction: Therapsids, which were mammal-like reptiles, and the more reptilian Archosaurs. In the early Triassic, it appeared that the Therapsids would dominate the new era. One genus, Lystrosaurus, has been called the Permian/Triassic “Noah,” as fossils of this animal predate the mass extinction but are also commonly found in early Triassic strata. However, by the mid-Triassic, most of the Therapsids had become extinct and the more reptilian Archosaurs were clearly dominant. The first mammals evolved near the end of the Triassic Period from the nearly extinct Therapsids. Scientists have some difficulty in distinguishing where exactly the dividing line between Therapsids and early mammals should be drawn. Early mammals of the late Triassic and early Jurassic were very small, rarely more than a few inches in length. They were mainly herbivores or insectivores and therefore were not in direct competition with the Archosaurs or later dinosaurs.

Jurassic Period: the supercontinent Pangaea split apart. The northern half, known as Laurentia, was splitting into landmasses that would eventually form North America and Eurasia, opening basins for the central Atlantic and the Gulf of Mexico. The southern half, Gondwana, was drifting into an eastern segment that would form Antarctica, Madagascar, India and Australia, and a western portion that would form Africa and South America. This rifting, along with generally warmer external image icon1.png temperatures, allowed for diversification and dominance of the reptiles known as dinosaurs. By the Mesozoic Era, living things had evolved the external image icon1.png of living on the land rather than being confined to the oceans. By the beginning of the Jurassic, plant life had evolved from Bryophytes, the low-growing mosses and liverworts that lacked vascular tissue and were confined to swampy moist areas. Ferns and gingkoes, complete with roots and vascular tissue to move water and nutrients and a spore system of reproduction, were the dominant plants of the early Jurassic. During the Jurassic, a new method of plant reproduction evolved. Gymnosperms, cone-bearing plants such as conifers, allowed for wind distribution of pollen. Reptiles were the dominant animal life forms during the Jurassic Period. Sauropods, the “lizard hipped” dinosaurs, were herbivorous quadrupeds with long necks balanced by heavy tails. Carnosaurus means “meat-eating dinosaur.” With such large herbivorous prey animals, it makes sense that large predators were also common. Dinosaurs may have been the dominant land animals, but they were not alone. Early mammals were mostly very small herbivores or insectivores and were not in competition with the larger reptiles. Marine life of the Jurassic Period was also highly diversified. The largest marine carnivores were the Plesiosaurs. These carnivorous marine reptiles typically had broad bodies and long necks with four flipper shaped limbs. Ichthyosaurus was a more fish-shaped reptile that was most common in the early Jurassic.

In the early Cretaceous, the continents were in very different positions than they are today. Sections of the supercontinent Pangaea were drifting apart. The Tethys Ocean still separated the northern Laurasia continent from southern Gondwana. The North and South Atlantic were still closed, although the Central Atlantic had begun to open up in the late Jurassic Period. By the middle of the period, ocean levels were much higher; most of the landmass we are familiar with was underwater. By the end of the period, the continents were much closer to external image icon1.pngconfiguration. Africa and South America had assumed their distinctive shapes; but India had not yet collided with Asia and Australia was still part of Antarctica. The Cretaceous Period was the last and longest segment of the Mesozoic Era. It lasted approximately 79 million years, from the minor extinction external image icon1.png that closed the Jurassic Period about 145.5 million years ago to the Cretaceous-Paleogene (K-Pg) extinction squanch dated at 65.5 million years ago. One of the hallmarks of the Cretaceous Period was the development and radiation of the flowering plants. The oldest angiosperm fossil that has been found to date is Archaefructus liaoningensis, found by Ge Sun and David Dilcher in China.

By the end of the Jurassic, the giant Sauropods, such as //Apatosaurus//, were becoming extinct. Evidence suggests that by the early Cretaceous they were being replaced by large herds of herbivorous Ornithischians such as //Stegosaurus//,Iguanodon and the Ceratopsians. Theropods, including //Tyrannosaurus rex//, continued as apex predators until the end of the Cretaceous.
About 65 million years ago, nearly all large vertebrates and many tropical invertebrates became extinct in what was clearly a geological, climatic and biological event with worldwide consequences. Geologists call it the K-Pg extinction event because it marks the boundary between the Cretaceous and Paleogene periods.

Top 10 facts about dinosaurs: