Dinosaur: Encyclopedia II - Dinosaur - Study of dinosaurs

Dinosaur - Study of dinosaurs

Information on dinosaurs is obtained from a widely varying fields of study which include Physics, Chemistry, Biology, and the Earth Sciences (which also includes Paleontology). Activities include the discovery, reconstruction and conservation of dinosaur fossils and the interpretation of those fossils which enables us to better understand the evolution, classification and behavior of dinosaurs.

Dinosaur - Classification

Main article: Dinosaur classification

Dinosaurs (including birds) are archosaurs, like modern crocodilians. Archosaurs' diapsid skulls have two holes located where the jaw muscles attach, called temporal fenestrae. Most reptiles (including birds) are diapsids; mammals, with only one temporal fenestra, are called synapsids; and turtles, with no temporal fenestra, are anapsids. Dinosaurs have teeth that grow from sockets (an archosaur characteristic) rather than as direct extensions of the jaw bones, as well as various other archosaur characteristics. Within the archosaur group, the dinosaurs are differentiated most noticeably by their gait. Instead of legs that sprawl out to the side, as found in lizards and crocodylians, they have legs held directly under their body. All dinosaurs were land animals.

Many other types of reptiles lived at the same time as the dinosaurs. Some of these are commonly, but incorrectly, thought of as dinosaurs, including plesiosaurs (which are not closely related to the dinosaurs) and pterosaurs, which developed separately from reptilian ancestors in the late Triassic period.

Dinosaurs are divided into two orders, the Saurischia and the Ornithischia, on the basis of their hip structure. Saurischians (from the Greek meaning "lizard hip") are dinosaurs that originally retained the hip structure of their ancestors. They include all the theropods (bipedal carnivores) and sauropods (long-necked herbivores). Ornithischians (from the Greek meaning "bird-hip") is the other dinosaurian order, most of which were quadrupedal herbivores.

The following is a simplified classification of dinosaurs familes. A more detailed version can be found at List of dinosaur classifications.

The dagger (†) is used to indicate taxa that are extinct.

Dinosaur - Order Saurischia

• †Family Herrerasauridae
• Suborder Theropoda
  • †Superfamily Coelophysoidea
  • †Superfamily Ceratosauria
    • †Family Abelisauridae
  • (unranked) Tetanurae
    • †Family Spinosauridae
    • †(unranked) Carnosauria
    • (unranked) Coelurosauria
      • †Family Coeluridae
      • †Superfamily Tyrannosauroidea
      • †Superfamily Ornithomimosauria
        • †Family Alvarezsauridae
      • (unranked) Maniraptora
        • †(unranked) Oviraptorosauria
          • †Superfamily Therizinosauria
        • †Superfamily Deinonychosauria
          • †Family Troodontidae
          • †Family Dromaeosauridae
          • †Family Microraptoria
        • Class Aves (birds)
• †Suborder Sauropodomorpha
  • †Thecodontosaurus
  • †Family Plateosauridae
  • †Riojasaurus
  • †(unranked) Sauropoda
    • †Family Diplodocidae
    • †(unranked) Macronaria
      • †(unranked) Titanosauriformes
        • †Family Brachiosauridae
        • †Family Titanosauridae

Dinosaur - †Order Ornithischia

• †Suborder Thyreophora
  • †Superfamily Stegosauria
  • †Superfamily Ankylosauria
• †Suborder Cerapoda
  • †Family Heterodontosauridae
  • †Superfamily Pachycephalosauria
  • †Superfamily Ceratopsia
    • †Family Psittacosauridae
    • †Family Protoceratopsidae
    • †Family Ceratopsidae
  • †Superfamily Ornithopoda
    • †Family Hypsilophodontidae
    • †Family Iguanodontidae
    • †Family Hadrosauridae

Dinosaur - Evolution

Dinosaurs split off from their archosaur ancestors approximately 230 million years ago during the early Triassic period, roughly 20 million years after the Permian-Triassic extinction event wiped out an estimated 95 percent of all life on Earth.^{[20] [21]} Radiometric dating of fossils from the early dinosaur species Eoraptor establishes its presence in the fossil record at this time. Paleontologists believe Eoraptor resembles the common ancestor of all dinosaurs; ^[22] if this is true, its traits suggest that the first dinosaurs were small, bipedal predators.^[23]

Also among the earliest dinosaurs was the primitive Lagosuchus; Saltopus, which was barely larger than a human hand, appeared slightly later. The first few lines of primitive dinosaurs diversified rapidly through the rest of the Triassic period; dinosaur species quickly evolved the specialized features and range of sizes needed to exploit nearly every terrestrial ecological niche. During the period of dinosaur predominance, which encompassed the ensuing Jurassic and Cretaceous periods, nearly every known land animal larger than 1 meter in length was a dinosaur.

The Cretaceous-Tertiary extinction event, which occured approximately 65 million years ago at the end of the Cretaceous period, caused the extinction of all dinosaurs except for the line that had already given rise to the first birds. Other diapsid species related to the dinosaurs also survived the event.

Adapted from the Wikipedia article "Study of dinosaurs", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki