Author's note: these pages were written some years ago. I am not planning to update them. For a more current coverage, see the link to palaeos com Palaeos website (to which many links on these pages point to anyway. More info here

Order Predentata (=Ornithischia)

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).

Predentata Classification

Originally only four suborders were distinguished - Ornithopoda, Stegosauria, Ankylosauria, and Ceratopsia.  Concerning which see: external link 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:

Genasauria cladogram
1. cheeks
2. armor
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
8. frill
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

diagram © by Professor Paul Olsen

Note that this cladogram only includes the external link  link to palaeos com 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].

Fabrosauria 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

Clade Thyreophora

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.

Scelidosauria Suborder Scelidosauria - Ancestral armoured types - mostly early Jurassic. Quadrapedal. Include light running forms and large heavily armed types. Length 1 to 4.5 meters

StegosauriaSuborder 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

AnkylosauriaSuborder Ankylosauria - heavily armoured dinosaurs, quadrapedal, slow moving, feed on swampy soft vegetation - mostly Cretaceous, length 2 to 10 meters

HeterodontosaursSuborder Heterodontosauria - mostly early Jurassic, small, fast-running bipedal herbivores - length about a metre. Possess tusks that were probably used for intraspecies combat

OrnithopodsSuborder 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.

Clade Marginocephalia

(Dome heads and horned dinosaurs)

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 link to palaeos com Laurasia.

Pachycephalosauria 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.

CeratopisaSuborder 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.

printed material Links Web links

Professor Paul Eric Olsen, Lecture 19 - The Late Cretaceous I - Mongolia

cladogram links link to palaeos com Ornithischia - Palaeos

cladogram Ornithischia (Predentata) - Justin Tweet's Thescelosaurus site

Jurassic Gallery Jurassic Gallery - fantastic artwork by M. Shiraishi, includes reconstructions of many dinosaurs. By Japanese and English

UCMPIntroduction to Thyreophora - the armored dinosaurs

UCMPIntroduction to Marginocephalia

internal link cautionary note (please read before using this page as reference material!)

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page history
page uploaded 9 July 1998
modified 20 August & 13 November
and again on 12 May 1999
and on 17 January 2000
converted to Style Sheet and page reorganised 12 January 2001, links updated 16 January 2010

content by M.Alan Kazlev