Ornithischia

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Ornithischia

[‚ȯr·nə′this·kē·ə]
(paleontology)
An order of extinct terrestrial reptiles, popularly known as dinosaurs; distinguished by a four-pronged pelvis, and a median, toothless predentary bone at the front of the lower jaw.

Ornithischia

 

an order of fossil reptiles of the superorder Dinosauria. The pubic bone of the tetraradiate pelvis had a developed posterior appendage (as in birds). The anterior, toothless part of the jaws was clad in a horny jacket and resembled a bill. The teeth were laterally compressed, with leaflike crowns. The distal phalanges of the digits in late ornithischians were flattened into hooves. The reptiles were herbivorous, with the earliest ones possibly being omnivorous. Many possessed defensive adaptations in the form of cutaneous scutella, spines, or horns. There were six (or four) suborders, including Stegosau-ria, Ankylosauria, and Ceratopsia. Ornithischians lived in the Jurassic and Cretaceous periods.

References in periodicals archive ?
The Early Jurassic ornithischian dinosaurian ichnogenus Anomoepus.
The Late Triassic pseudosuchian Revueltosaurus callenderi and its implications for the diversity of early ornithischian dinosaurs.
After ornithischian tooth remains were reidentified as coming from crocodile-like creatures and not dinosaurs, the evidence for this group in the late Triassic was whittled down to just three body fossils from a small area of southern Gondwana.
All previous feathered theropods belong to the saurischian order, whereas the new fossil belongs to the ornithischian.
The find "pulls the origin of feathers down into the Triassic, when the saurischian and ornithischian lineages of dinosaurs split", said Philip Currie at the University of Alberta in Canada.
Because the various groups had such dissimilar anatomies, early dinosaur investigators presumed that the bird-hipped ornithischians had evolved from a different stock of reptiles than had the sauropods and theropods, which together form a group called saurischian dinosaurs, characterized by their lizard-like pelvises.
The two researchers showed that some saurischians and ornithischians had remarkably similar joints, indicating that the earliest members of these two lineages had sprung from one line of animals that bore features common to both groups.
According to Sereno, the primitive nature of the Eoraptor skull supports the theory that dinosaurs arose from a common ancestor and only later developed specializations that would split them into ornithischians and saurischians.
By the time of Eoraptor, during the rnid-Carnian stage of the Triassic period, dinosaurs had already split into the major groups of carnivorous theropods and herbivorous ornithischians.