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What is Ornithischia?

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Dinosauria
Ornithischia
Pronunciation: or-ni-THIS-kee-uh
Author: Harry Seeley
Year: 1888
Meaning: Bird hips (see etymology)
Locomotion: Some two legs, some four legs
Synonyms: Predentata (Marsh, 1894)
(Padian and May, 1993)Definition
All dinosaurs closer to Triceratops than to birds.
In a nutshell
Ornithischia is an extinct order of beaked, herbivorous, "bird-hipped" dinosaurs.
About
Way back in 1887 Harry Govier Seeley split all dinosaurs into two main branches based on the design of their hips; Saurischia — the "lizard-hipped" dinosaurs whose pubis bone points forward at an angle to the ischium, towards the creature's head, and Ornithischia — the "bird-hipped" dinosaurs whose pubis bone runs parallel with the ischium towards the creature's tail, but also has a forward-pointing process to support the abdomen.

Apart from the unique structure of their hips, which are not only wider than those of saurischians but also sport at least five vertebrae that are fused to form the sacrum, ornithischian's have smaller fenestrae ("windows") in front of their eye sockets than saurischians and an extra bone called the predentary (before dentary) at the front of the lower jaw (dentary). This bone mirrors the premaxilla (before maxilla), a bone at the end of the upper jaw (maxilla), and together they formed a "beak" for clipping plant material. All ornithischians have broad leaf-shaped teeth with large denticles and ate plants, but some also sported canines and may have been omnivorous.

Ornithischia includes Ornithopoda (including the spike-thumbed iguanodonts and duck-billed hadrosaurs), Thyreophora (including the plated stegosaurs and armoured ankylosaurs) and Marginocephalia (including the horned ceratopsians and head-banging pachycephalosaurs). Funnily enough, although named for its member's bird-like hip structure Ornithischia doesn't include birds. Birds belong to Saurischia (the "lizard-hipped" dinosaurs) which is confusing enough. But to complicate matters further, the pot-bellied therizinosauroids and ostrich-mimicking ornithomimids who have beaks, and the therizinosauroids and bird-like dromaeosaurids who later evolved bird-like hips, don't belong to Ornithischia either!

Ornithischia is one of the two great lineages of herbivorous dinosaurs. They were nowhere near as big as the members of Sauropoda (the other lineage, from Saurischia), but just like smaller, modern herbivores, they were higher in species and number so carnivores always had plenty of fodder.

Click here to search Dinochecker's database for Ornithischia.
Etymology
Ornithischia is derived from the Greek "ornith" (bird) and "iskhion" (hip joint).
Relationships
References
Seeley HG (1887) "On the classification of the fossil animals commonly named Dinosauria". P R Soc London. 43:165–171.
Thomas R. Holtz, Jr (2008) "The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages".
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To cite this page:
Atkinson, L. "DinoChecker FAQ entry :: What is Ornithischia?"
http://www.dinochecker.com/dinosaurfaqs/what-is-ornithischia›. Web access: 25th Jun 2017.
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