The Predentata or Ornithischia are a very diverse group of dinosaurs distinguished by their bird-shaped hips and the presence of an extra bone (the predentry) in the front of the low jaw (hence the two names for them - "Ornithischia" is the older name). Many types evolved ungulate (hooved) mammal-like features like elaborate batteries of chewing teeth, and horns and other types of crests and head ornaments (used not so much against preditors as in intra-specific rivalry - competition for mates, etc).
Originally only four suborders were distinguished - Ornithopoda, Stegosauria, Ankylosauria, and Ceratopsia. Concerning which see: Ornithischian Dinosaurs - a gif file showing the original four main types (185 kb)
More recently some of these groups have been shown to be related and hence united under larger sub-ordinal groups, while new groups are also required by modern discoveries.
The three main (large) clades of Ornithischian (Predentata) dinosaurs are the Thyreophora or armoured dinosaurs, the Ornithopoda or mostly bipedal, typical plant-eaters, and the Marginocephalia or horned and bone-head forms. Here is another breakdown of Ornithischian systematics:
3. armor as plates covering back
4. armor as spikes or plates
5. uneven enamel
6. back part of skull makes shelf
7. rostral bone
9. reduced hands
10. domed head
11. jaw joint below tooth row
12. elongate hands
13. prepubic process well developed
14. ridge on teeth
15. reduction in manus digits I and V (and large nares)
16. manus digit 1 spike-like
Note that this cladogram only includes the Genasauria and not some more primitive forms like the Fabrosauria.
The current cladistic paradigm has meant these early types, like Fabrosaurs and Heterodontosaurs have been stuck as "outgroups" with no linnean status beyond family level. Since these early groups differ at least as much as the later ones I decided to take matters into my own hands and christen them as new suborders [ Stanley Friesen's Dinosaur classification follows a similiar tack].
Suborder Fabrosauria - small early ancestral forms - active fast-running lightly-built bipeds, ancestral to all other Ornithschian lineages, late Triassic to early Jurassic - length about a metre
These are small to large specialised quadrapedal armoured forms - early Jurassic to late Cretaceous - length one to ten metres. There are three main subgroups: the primitive ancestral Scelidosaurs, the unusual Stegosaurs, and the heavily armoured Anklyosaurs. It has been suggested that the Stegosaurs are actually more closely related to the Ornithopods, but generally the following three lineages are grouped together, with the scelidosaurs as the basal (paraphyletic) grade from which the other two clades developed.
Suborder Scelidosauria - Ancestral armoured types - mostly early Jurassic. Quadrapedal. Include light running forms and large heavily armed types. Length 1 to 4.5 meters
Suborder Stegosauria - plated dinosaurs - mostly Jurassic, spines along the back and tail for protection, plates served a thermoregulatory purpose. Quadrapedal, short forelimbs, slow-moving. Length 4 to 10 meters
Suborder Ankylosauria - heavily armoured dinosaurs, quadrapedal, slow moving, feed on swampy soft vegetation - mostly Cretaceous, length 2 to 10 meters
Suborder Heterodontosauria - mostly early Jurassic, small, fast-running bipedal herbivores - length about a metre. Possess tusks that were probably used for intraspecies combat
Suborder Ornithopoda - small to large generalised mostly bipedal herbivores, late Jurassic to late Cretaceous. Can be divided into the small, less specialised, Hypsilophodontia, and the larger (often 6 to 8 meters, weights of several tonnes) Iguanodontia (divided in turn into the Dryosauroidea and the Iguanodontoidea. One line of Iguanodontia, the Hadrosaurs or "duck-bill" dinosaurs, developed distinctive crests that were probably used for intraspecies communication.
The Marginocephalia or "fringed heads" were a specialised group of Ornithischians defined by a small shelf or frill at the back of their skull. There are two main types, the dome heads and the horned dinosaurs, which evolved from a common ancestor during the early Cretaceous. With the exception of one or two questionable Gondwana forms, the group appears to be limited to Laurasia.
Suborder Pachycephalosauria - dome headed dinosaurs, superficially resemble the ornithopods; bipedal, small to medium-sized, with a bony "battering ram" that was probably used in fites over territory or mates.
Suborder Ceratopisa - horned dinosaurs, small to large parrot-beaked dinosaurs, divided into the primitive early Psittacosauria - parrot-beaked dinosaurs, stocky animals about about 1.5 meters long, and the Neoceratopsia or horned dinosaurs, including both horned and hornless types, all equipped with a bony frill, and the medium-sized to larger ones quadrapedal. Included here area number of famous late Cretaceous types like Styracosaurus, Triceratops, etc.
Professor Paul Eric Olsen, Lecture 19 - The Late Cretaceous I - Mongolia
Ornithischia - Palaeos
Ornithischia (Predentata) - Justin Tweet's Thescelosaurus site
Jurassic Gallery - fantastic artwork by M. Shiraishi, includes reconstructions of many dinosaurs. By Japanese and English
Introduction to Thyreophora - the armored dinosaurs
Introduction to Marginocephalia
cautionary note (please read before using this page as reference material!)
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