Dinosaurs

1. Dinosaurs lived from about 245 to 65.5 million years ago. They were common during the Triassic, Jurassic, and Cretaceous geologic time periods.

1.1. Triassic: the first geological period in the Mesozoic era. It lasted 50 million years. The period began 252.17 million years ago, and ended 201.3 million years ago. Many new groups arose during the Triassic period, including the dinosaurs and the first mammals

1.2. Jurassic: The Jurassic is the second geological period in the Mesozoic era. It began 201.3 million years ago, and ended 145 million years ago. The Jurassic period happened between the Triassic and Cretaceous periods.

1.3. Cretaceous: The Cretaceous period lasted 80 million years from 145 to 66 million years ago. It followed the Jurassic period, and is the latest period of the Mesozoic era. At its end came the famous meteorite strike which, with the volcanic flood basalts spewed out in the Deccan and ended so many of the dominant life-forms.

2. Dinosaurs had adaptations which helped make them successful. The first known dinosaurs were small predators that walked on two legs. All their descendents had an upright posture, with the legs underneath the body. This transformed their whole life-style. There were other features. Most of the smaller dinosaurs had feathers, and were probably warm-blooded. This would make them active, with a higher metabolism than modern reptiles. Social interaction, with living in herds and co-operation seems very likely for some types.

3. Dinosaurs, a type of Archosaur reptile, were the dominant land animals of the Mesozoic era. Over 500 different genera of dinosaurs have been found. Fossils of dinosaurs have been found on every continent, and there are still frequent new discoveries.

4. Dinosaurs are united by at least 21 traits in their skulls and skeletons. These common characters (called 'synapomorphies') are the reason palaeontologists are sure dinosaurs had a common origin. However, when definite dinosaur fossils appear (early in the Upper Triassic), the group had already split into two great orders, the Saurischia, and the Ornithischia. The Saurischia keep the ancestral hip arrangement inherited from their Archosaur ancestors, and the Ornithischia have a modified hip structure.

4.1. Saurischia: this is the order of dinosaurs with the ancestral pelvis (hips). Theropods: this is the group of carnivorous dinosaurs. Sauropods: these were large herbivorous dinosaurs with long necks.

4.2. Ornithischia: this is an order of beaked, herbivorous dinosaurs with bird-like hips. Armoured dinosaurs: these are dinosaurs with their backs protected by plates of bone. Ankylosauria: dinosaurs with flat plates of armour. Stegosauria: the stegosaurs.

4.3. Cerapoda: three rather different groups: Ornithopoda: the duck-billed dinosaurs. Pachycephalosauria: the thick-headed dinosaurs. Ceratopsia: the horned dinosaurs, like Triceratops.