Background information
Dinosaurs lived from 230-65 million years ago, in a time period known as the Mesozoic Era. For a profound understanding, scientists divided the Mesozoic era into three periods: Triassic, Jurassic and Cretaceous. The dinosaur first appeared in the Triassic Period was Megalosaurus. Dinosaurs have lived on all the continents in the world, due to the super continent Pangea. This period lasted over millions of years, during this period new dinosaurs evolved while some went extinct. In the Mesozoic Era dinosaurs such as Tyrannosaurus rex and Triceratops existed during the cretaceous period. With the discovery of many new species since the 1840s, the Dinosauria now contains two major groups of dinosaurs: the Saurischia, or "lizard-hipped" dinosaurs or the Ornithischia, commonly known as "bird-hipped" dinosaurs.
Dinosaurs lived from 230-65 million years ago, in a time period known as the Mesozoic Era. For a profound understanding, scientists divided the Mesozoic era into three periods: Triassic, Jurassic and Cretaceous. The dinosaur first appeared in the Triassic Period was Megalosaurus. Dinosaurs have lived on all the continents in the world, due to the super continent Pangea. This period lasted over millions of years, during this period new dinosaurs evolved while some went extinct. In the Mesozoic Era dinosaurs such as Tyrannosaurus rex and Triceratops existed during the cretaceous period. With the discovery of many new species since the 1840s, the Dinosauria now contains two major groups of dinosaurs: the Saurischia, or "lizard-hipped" dinosaurs or the Ornithischia, commonly known as "bird-hipped" dinosaurs.
Classification
There are two main categories in which dinosaurs are classified: Ornithischia and Saurischia. Ornithischia popularly known as "Bird hipped" dinosaurs have three main sub catergories: Thyreophora, Marginocephalia and Ornithopoda. Whereas, Saurischia or popularly known as “lizard hipped dinosaurs” were herbivores and are divided into two sub categories Sauropodomorpha and Theropoda
There are two main categories in which dinosaurs are classified: Ornithischia and Saurischia. Ornithischia popularly known as "Bird hipped" dinosaurs have three main sub catergories: Thyreophora, Marginocephalia and Ornithopoda. Whereas, Saurischia or popularly known as “lizard hipped dinosaurs” were herbivores and are divided into two sub categories Sauropodomorpha and Theropoda
Ornithischia contains several groups of herbivorous dinosaurs, including several basal groups, but primarily three large ones, Thyreophora, Marginocephalia and Ornithopoda. Ornithischia contains several groups of herbivorous dinosaurs, including several basal groups, but primarily three large ones: Thyreophora, Marginocephalia, Ornithopoda.
Thyreophora includes the various armored dinosaurs, like Stegosaurus and Ankylosaurus.
Marginocephalia consists mainly of the pachycephalosaurs (bone-heads) and theceratopsians (horned dinosaurs), like Triceratops.
Ornithopoda is the third Ornithischian group, and includes small bipedal plant-eaters like Heterodontosaurus, but also the often large hadrosaurs, or "duck-billed dinosaurs," like Maiasaura..
The category Saurischia contains two main groups, Sauropodomorpha and Theropada: Sauropodomorpha is the first group, and includes both the "prosauropods" — a group of largely herbivorous, dominantly quadrupedal dinosaurs such as Plateosaurus; and the Sauropoda: long-necked, long-tailed, enormous herbivorous dinosaurs like Apatosaurus, Brachiosaurus, and Diplodocus. Theropoda is the second saurischian group, consisting of the carnivorous dinosaurs. The Theropoda includes some extinct dinosaurs such as Tyrannosaurus rex and Dilophosaurus, but it also includes the living dinosaurs — the birds.
Extinction
There are a few theories explaining the causes of the dinosaur extinction. Some of these theories are:
Dinosaurs evolved around 230 million years ago and had lived throughout the Mesozoic period. The extinction occurred towards the end of the Cretaceous period which was the longest and the last period of the Mesozoic era. It is believed that it took 165 million years for the complete dinosaur extinction to occur.
There are a few theories explaining the causes of the dinosaur extinction. Some of these theories are:
- Atomictheory - According to this theory a large asteroid or comet collided with Earth about 65 million years ago. Scientists think that such a large collision would throw so much dust into the air that sunlight would not be able to shine and plants and animals would die.
- The dramatic changes in climate that resulted from this huge collision were too much for the dinosaurs.
- Volcanic activity - Another theory that could explain how the dinosaurs became extinct is volcanic activity. A huge increase in volcanic activity at around 65 millions years ago could have pumped so much ash into the air that it blocked out the sun killing the dinosaurs.
- Ice Age - Some scientists believe that there was a severe ice age. Throughout Earth's history there have been many ice ages. The last one ended about 10,000 years ago. A very severe ice age could have changed temperatures and frozen a lot of Earth's water. The dinosaurs would not be able live under such conditions and that is how the dinosaurs became extinct
- Disease - It has also been suggested that disease killed off the dinosaurs. A very deadly and contagious disease may have circulated among the dinosaurs forcing them to become extinct.
Dinosaurs evolved around 230 million years ago and had lived throughout the Mesozoic period. The extinction occurred towards the end of the Cretaceous period which was the longest and the last period of the Mesozoic era. It is believed that it took 165 million years for the complete dinosaur extinction to occur.