Origin and Evolution of Reptiles

1. Origin and Evolution of Reptiles Introduction

2. Introduction • From studies of fossils and comparative anatomy, zoologists infer that reptiles arose from amphibians. • The oldest known fossils of reptiles are about 350 million-years-old. • They were found in deposits from the early carboniferous period, which occurred between 360 and 286 million years ago. Casineria – the earliest known amniote

3. Introduction • The earliest reptiles were small, four legged vertebrates that resembled lizards and had teeth adapted for eating insects. The abundance of insects at the time may have been one reason that early reptiles flourished.

4. Age of Reptiles • The reptiles diversified rapidly, and by the Permian period (286 million to 245 million years ago) they had become the dominant land vertebrates. • The Mesozoic era (245 million to 65 million years ago) is often called the Age of Reptiles because nearly all of the large vertebrates on Earth were reptiles during that time. Plesiosaurus

5. Age of Reptiles • On land, the most famous and spectacular reptiles – the dinosaurs – appeared and evolved into a great variety of forms during the Mesozoic era. • Dinosaurs are known for the great size of some species. One of the largest dinosaurs, Brachiosaurus, measured 23 m (75ft) in length, stood 12 m (40 ft) tall, and weighed more than 77,000 (170,000 pounds). Many species of dinosaurs, however, were small, some no larger than chicken.

6. Age of Reptiles • Over 300 species of dinosaurs have been identified. Their fossils have been discovered on all continents, even Antarctica, which had a much warmer climate during the Mesozoic era than it does today. • Dinosaurs were adapted to a wide range of environments and to different ways of life.

7. Age of Reptiles • Reptilian success during the Mesozoic era was not limited to terrestrial habitats. Several groups of reptiles, including Ichthyosaurs and Plesiosaurs, lived in the oceans.

8. Age of Reptiles • Ichthyosaurs were sleek reptiles that resembled modern bottlenose dolphin. Plesiosaurs had long, flexible necks and compact bodies. Plesiosaurus Ichthyosaurus found in Somerset County, England.

9. Extinction of Dinosaurs • Although the fossil record provides many clues about what dinosaurs were like. Paleontologists who study dinosaurs still have many unanswered questions. For example, why did the dinosaurs become extinct 65 million years ago, at the end of the cretaceous period? • Many species of aquatic and terrestrial organisms besides the dinosaurs became extinct at this time.

10. Extinction of Dinosaurs • Most scientists think that a catastrophic cosmic event was responsible for the mass extinction. Supporters of this hypothesis – called the asteroid-impact hypothesis – suggest that a huge asteroid hit the earth, sending so much dust into the atmosphere that the amount of sunlight reaching the earth’s surface was greatly reduced.

11. Extinction of Dinosaurs • The reduced sunlight causes severe climate changes that led to the mass extinction. • According to this hypothesis, the dinosaurs would have become extinct very quickly, perhaps even with a few months.

12. Success of Reptiles • Representatives of the four modern orders of reptiles—turtles and tortoises, lizards and snakes, tuataras, and crocodilian—survived the mass extinction of the Cretaceous period. • These four orders of reptiles have diversified to more than 5,000 species.

13. Success of Reptiles • Reptiles today successfully occupy a variety of terrestrial and aquatic habitats on all continents except Antarctica. Evolution