What is a Dinosaur? Over 65 million years ago dinosaurs roamed the earth. Dinosaurs inhabited earth long before man existed. From the early dinosaurs, Archosaurs, to the massive Sauropods and carnivorous Tyrannosaurids, dinosaurs have inspired the research of scientists and captured the imagination of many, young and old. Dinosaurs ruled the world during the Mesozoic Era, which is divided into three Periods. During the Triassic Period, dinosaur ancestors were evolving. In the Late Triassic, the world saw the first true dinosaurs. In the Jurassic Period, the number of dinosaurs grew. By the Cretaceous Period, many different types of dinosaurs had evolved. Paleontologists study the different kinds of dinosaurs to find their relationships to other dinosaurs and to find the ancestors of the dinosaurs. This can tell scientists much about evolution. It can also tell them some things about the world the dinosaurs lived in. Dinosaurs that could migrate were similar, but those dinosaurs that were isolated evolved differently from their relatives on other continents. The largest dinosaurs were over 100 feet (30 m) long and up to 50 feet (15 m) tall (like Argentinosaurus, Seismosaurus, Ultrasauros, Brachiosaurus, and Supersaurus). The smallest dinosaurs, like Compsognathus, were about the size of a chicken. Most dinosaurs were in-between. There were lots of different kinds of dinosaurs that lived at different times. Some walked on two legs (they were bipedal), some walked on four (they were quadrupedal). Some could do both. Some were speedy (like Velociraptor), and some were slow and lumbering (like Ankylosaurus). Some were armor-plated, some had horns, crests, spikes, or frills. Some had thick, bumpy skin, and some even had primitive feathers. The dinosaurs dominated the Earth for over 165 million years during the Mesozoic Era, but mysteriously went extinct 65 million years ago. Paleontologists study their fossil remains to learn about the amazing prehistoric world of dinosaurs. Dinosaurs were reptiles and most hatched from eggs. No dinosaurs could fly and none lived in the water. Plant-eating sauropods were the largest animals to ever walk on Earth - but blue whales are more massive than any of the dinosaurs were! Most dinosaurs were plant-eaters (also called herbivores). For example, Triceratops was a plant-eating dinosaur. Some dinosaurs were meat-eaters (also called carnivores). For example, T. rex was a meat-eating dinosaur. Dinosaur Timeline Earth history is divided into chunks of time, most importantly aeons, eras and periods. Dinosaurs and other prehistoric reptiles were the dominant animals for about 185 million years during the Mesozoic era, which was a section of the Phanerozoic aeon. More simply, the Mesozoic era lasted from 250 million years ago to 65 million years ago, and contained three periods called the Triassic, Jurassic and Cretaceous. The first reptiles appeared during the Palaeozoic Era (570 million to 245 million years ago), just before the Mesozoic Era (245 million to 65 million years ago). Each of these eras is divided up into sections called periods. Palaeozaic era (pall-ay-oh-zoh-ick) 1. The first fishes, Cambrian period: corals, trilobites (570 million years and shellfish ago) appeared. Right: Fossil trilobites 2. The first nautiloids Ordovician period: appeared. Corals A fossil nautiloid (505 million years and trilobites were ago) common. The Age of Dinosaurs (2002). [Online], Available: www.kidcyber.com.au 3. The first land plants Silurian period: and giant sea (438 million years scorpions called ago) Eurypterids appeared. 4. The first Devonian period: amphibians, insects (408 million years and spiders Fossil of a plant called ago) appeared. Archaeopteris from the Devonian period 5. The first reptiles Carboniforous appeared. Great period: (360 million swamp forests years ago) covered the land. 6. The first sailback Permian period: reptiles such as (286 million years Dimetrodon (right) ago) appeared. The Age of Dinosaurs (2002). [Online], Available: www.kidcyber.com.au Mesozaic era (mezo-zay-ick) 1. The first dinosaurs Triassic period: such as 245 million years Coelophosis and ago Euskelosuaurus and mammals, turtles, crocodiles and frogs appeared. 2. The first birds Jurassic Period: appeared (e.g. (208 million years Archaeopteryx). ago) Dinosaurs included diplodocus, stegasaurus, brachiosaurus 3. Dinosaurs during Cretaceous this time included period: (144 million muttaburrasaurus, years ago) quetsalcoatlus, ankylosaurus. The dinosaurs died out towards the end of this period. The first snakes and modern mammals appeared. The Age of Dinosaurs (2002). [Online], Available: www.kidcyber.com.au All through this time the earth was changing. In the Triassic period, all the continents were joined together in one huge landmass. Climate was hot and dry but with rain seasons. The first tree ferns and coniferous trees were starting to appear. In the Jurassic period the climate changed as the huge continent was breaking up. There were now forests of cycads, conifers and gingko, all plants that still exist today. In the Cretaceous period the continents had separated and each had its own flora and fauna. However Australia and Antarctic were still joined together. There were now flowering plants such as magnolias and water lilies. The Age of Dinosaurs (2002). [Online], Available: www.kidcyber.com.au Dinosaur Time Line Dinosaurs, mammals Birds Dinosaurs People evolve evolve go extinct evolve Triassic Jurassic Cretaceous Period Period Period Mesozoic Era Cenozoic Era 248 mya 206 mya 144 mya 65 mya Now Millions of Years Ago .