Dinosaur

Dinosaurs were a superorder of reptiles that first appeared approximately 210 million years ago. Their reign encompassed the Triassic, Jurassic, and Cretaceous periods, a time period spanning over 150 million years. At the end of the Cretaceous, 65 million years ago, most species of dinosaur become extinct (the Cretaceous-Tertiary extinction event), but there is considerable evidence to suggest that modern birds are the descendants of dinosaurs.

The formal name Dinosauria was first proposed by the English scientist Richard Owen in 1842. The term is a combination of the Greek words deinos ("terrible" or "fearfully great" or "formidable") and sauros ("lizard" or "reptile").

Dinosaurs varied greatly in size. The smallest known species were about the size of a chicken, but most were much larger. The biggest dinosaurs were the Sauropoda; they were the largest land animals ever to live, and overall are second in size only to certain species of whale.

Many other types of reptiles lived at the same time as the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs: these include plesiosaurs (which are not closely related to the dinosaurs), and Pterosaurs (which may have been).

The extinction of the dinosaurs is one of the most intriguing problems in paleontology. Only recently has the nature of this extinction become apparent. The extinction appears to have been rapid, and besides the dinosaurs, other groups, including ammonites, mosasaurs, plesiosaurs, pterosaurs, herbivorous turtles and crocodiles, most kinds of bird, and many groups of mammals, became extinct. The bulk of the evidence now indicates that this extinction event is linked to the impact of a meteorite or comet 65 million years ago (a theory first proposed by Walter Alvarez). The survivors of this mass extinction appear to have been two things that dinosaurs in general were not: small and/or aquatic.

Classification of dinosaurs

Dinosaurs are divided into two major orders, the Saurischia and the Ornithischia, on the basis of hip structure.

Saurischia
- Theropoda
  - Ceratosauria (e.g. Coelophysis, Procompsognathus, Dilophosaurus, Abelisaurus)
  - Spinosauridae (e.g. Spinosaurus)
  - Allosauridae (e.g. Allosaurus)
  - Coelurosauria
    - Tyrannosauridae (e.g. Tyrannosaurus rex, Albertosaurus)
    - Ornithomimidae (e.g. Ornithomimus, Struthiomimus, Gallimimus)
    - Oviraptoridae (e.g. Oviraptor)
    - Therizinosauridae (e.g. Therizinosaurus, Segnosaurus)
    - Troodontidae (e.g. Troodon)
    - Dromaeosauridae (e.g. Deinonychus, Velociraptor)
    - Aves (birds)
- Sauropodomorpha
  - Plateosauridae (e.g. Plateosaurus)
  - Sauropoda
    - Diplodocidae (e.g. Apatosaurus, Diplodocus, ?Mamenchisaurus?)
    - Brachiosauridae (e.g. Brachiosaurus)
    - Titanosauridae (e.g. Titanosaurus, Saltasaurus)
Ornithischia
- Thyreophora
  - Stegosauria (e.g. Stegosaurus)
  - Ankylosauria (e.g. Ankylosaurus, Euplocephalus, Nodosaurus, scolosaurus)
- Neornithischia
  - Ornithopoda (e.g. Anatosaurus, Parasaurolophus, Hypsilophodon, Iguanodon)
  - Pachycephalosauria (e.g. Pachycephalosaurus)
  - Ceratopia (e.g. Psittacosaurus, Protoceratops, Triceratops)

External links

For the most comprehensive family tree of dinosaurs yet available, see

For the Dinosauria On-Line Dinosaur Omnipedia, with dictionaries of terms, pronunciations, maps and cladograms, see

http://www.dinosauria.com/dml/dml.htm#toc

Active research Museum with 35 complete skeletons and more than 110,000 specimens

http://www.tyrrellmuseum.com (Royal Tyrrell Museum of Palaeontology)

This BBC page contains a huge amount of accurate and comprehensible information and pictures

http://www.bbc.co.uk/dinosaurs/

Other Meanings

Charlene and Robbie in episode Refrigerator Day

Dinosaur is sometimes used as a derogatory term to describe things that are perceived as being out of date or no longer in touch with the spirit of the times, and therefore ought to be extinct. An example was the manner in which the punk movement described the 'progressive' bands that preceded them as 'dinosaur groups'. Considering that dinosaurs were actually highly successful life forms for some 150 million years, this term could be seen as quite ironic. It is even more ironic when one considers that birds are most probably direct descendants of dinosaurs, which implies that not only the dinosaurs aren't extinct (in the sense of, say, trilobites), but also that their modern descendants are themselves a highly successful group that have been able to colonize almost every habitat on the planet.

Dinosaurs was also a sitcom television series from Jim Henson Productions.