Side-Green.Com - Modern Definition of Dinosaurs - Under phylogenetic taxonomy, dinosaurs are usually defined as the group consisting of "Triceratops, Neornithes (modern birds), their most recent common ancestor, and all descendants." It has also been suggested that Dinosauria be defined with respect to the most recent common ancestor of Megalosaurus and Iguanodon, because these were two of the three general cited by Richard Owen when he recognized the Dinosauria.
Both definitions result in the same set of animals being defined as dinosaurs, including:
- theropods (mostly bipedal carnivores)
- sauropodomorphs (mostly large herbivorous quadrupeds with long necks and tails)
- ankylosaurians (armored herbivorous quadruped)
- stegosaurians (plated herbivorous quadrupeds)
- ceratopsians (herbivorous quadrupeds with horn and frills)
- ornithopods (bipedal or quadrupedal herbivores including "duck-bills")
These definitions are written to correspond with scientific conceptions of dinosaurs that predate the modern use of phylogenetics. The continuity of meaning is intended to prevent confusion about what the term "dinosaur" means.
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| Triceratops skeleton at the American Museum of Natural History in New York City |
There is wide consensus among paleontologist that birds are the descendants of theropod dinosaurs. Using the strict cladistical definition that all descendants of a single common ancestor must be included in a group for that group to be natural, birds would thus be dinosaurs and dinosaurs are, therefor, not extinct. Birds are classified by most paleontologists as belonging to the subgroup Maniraptora, which are coelurosaurs, which are theropods, which are saurischians, which are dinosaurs.
From the point of view of cladistics, birds are dinosaurs, but in ordinary speech the word "dinosaur" does not include birds.Additionally, referring to dinosaurs that are not birds as "non-avian dinosaurs" is cumbersome. For clarity, this article will use "dinosaur as a synonym for "non-avian dinosaur". The term "non-avian dinosaur" will be use for emphasis as needed.
See also:
This article about dinosaurs quoted from userpages.umbc.edu