A dinosaur (Meaning "terrible lizard") is any terrestrially-dwelling, upright-walking reptile from the Mesozoic era. Dinosaurs are classified in two main orders, Saurichia and Ornichia.
Dinosaurs and Non-DinosaursEdit
Many creatures have been given the label of "dinosaur," most prominently the "pterodactyls," more formally known as pterosaurs ("Pterodactyl" is used to specifically describe advanced pterosaurs.). While pterosaurs are believed to share a common ancestor with dinosaurs, they themselves are not dinosaurs. Other reptiles believed to be dinosaurs are mosasaurs, plesiosaurs, and ichyosaurs, popular marine reptiles. However, mosasaurs are actually more closely related to lizards and snakes, and plesiosaurs and ichyosaurs belong to their own distinct reptile groups. A creature known as Dimetrodon (Pronounced di-me-tro-don) has also been called a dinosaur, but it is actually more closely related to mammals, and may not even be a reptile. The difference? Pterosaurs are aerial reptiles, mosasaurs, plesiosaurs, and ichyosaurs are all marine reptiles, and Dimetrodon has a sprawling stance. Dinosaurs are defined as being strictly terrestrial creatures with an upright stance ("Upright stance," of course, meaning that their legs are directly underneath the body, as opposed to the sides.). Additionally, dinosaurs are strictly from the Mesozoic era, specifically from the Late Triassic to the very end of the Cretaceous, and Dimetrodon is from the Permian, which came before the Triassic.
Dinosaurs and BirdsEdit
Although dinosaurs usually strictly follow the above guidelines, some Late Jurassic dinosaurs are believed to have evolved gliding capability, then powered flight, becoming the very first flying dinosaurs. These dinosaurs are believed to be the precursors of birds, some of which (Such as penguins) became the very aqueous dinosaurs (Though some other dinosaur groups may have done some swimming.).
It has been long debated whether dinosaurs are warm- or cold-blooded. However, a new theory states that they were intermediate between the two metabolisms. After all, they were intermediate between birds and reptiles. Additionally, an intermediate metabolism would explain the lack of air and water dinosaurs, as an intermediate metabolism would not produce enough heat for water, nor enough activity for flight. It would even explain their great size. You see, cold-blooded creatures devote most of their matter and energy towards production, not maintenance, whereas warm-blooded creatures are just the opposite. Being in between these would create a balance between production and maintenance, allowing enough matter and energy for great size, and enough activity to maintain it.
Basic Dinosaur ClassificationEdit
- Unranked Crocodylotarsi (Crocodiles and relatives)
- Unranked Ornithodira
- Order Pterosauria
- Superorder Dinosauria
- Order Ornithchia
- Order Saurichia
- Suborder Sauropodomorpha (Sauropods and relatives)
- Suborder Theropoda (Carnivorous dinosaurs)
- Unranked Coleurosauria
- Class Aves (Birds)