Evolution of Reptiles

Shafi ul Haq

UNIVERSITY OF HARIPURDEPARTMENT OF FORESTRY & WILDLIFE MANAGEMENT

IntroductionFrom 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

IntroductionThe 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.

Age of ReptilesThe 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

Age of ReptilesOn 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.

Age of ReptilesOver 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.

Age of ReptilesReptilian success during the Mesozoic era

was not limited to terrestrial habitats. Several groups of reptiles, including Ichthyosaurs and Plesiosaurs, lived in the oceans.

Age of ReptilesIchthyosaurs were sleek reptiles that

resembled modern bottlenose dolphin. Plesiosaurs had long, flexible necks and compact bodies.

Ichthyosaurus found in Somerset County, England.

Plesiosaurus

Extinction of DinosaursAlthough 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.

Extinction of DinosaursMost 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.

Extinction of DinosaursThe 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.

Success of ReptilesRepresentatives 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.

Success of ReptilesReptiles today successfully occupy a variety

of terrestrial and aquatic habitats on all continents except Antarctica.

Evolution

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