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

Suborder Ornithopoda

The middle Cretaceous ornithopod Iguanodon (length 7 to 8 meters)
artwork © Seiji Yamamoto, reproduced with permission

The single most important group of middle to late Mesozoic terrestrial herbivores, the Ornithopods include a diverse range of small to very large generalised mostly bipedal herbivores, from the middle Jurassic to late Cretaceous periods, and ranging in size from less than a meter to over fourteen metres in length. At one time they were considered the ancestral types from which the other lines of Ornithischia developed.  But nowadays the Fabrosaurs are considered distinct from the rest of the Ornithopoda and the ornithopods lost their ancestor status.  Even heterodontosaurs, previously considered typical Triassic Ornithopods, are now sometimes considered a specialised early off-shoot, ornithopod cousins rather than true ornithopods. If that is so, the ornithopod stratigraphic range is greatly reduced. It may be that the early hypsilophodontids evolved directly from Fabrosaurs, in paralel with but later than the Heterodontosaurs.

The more specialised Ornithopods (Iguanodontia) had very elaborate rows of teeth and developed a sophisticated means of chewing their food.  Many Hadrosaurids also developed strange crests on their snouts or the top of their heads.  The Ornithopods were very much the reptilian Mesozoic equivalents of the Cenozoic mammalian ungulates (hooved mammals).  Even their clawed feet became blunt and hooflike.

Suggested Ornithopod classification:

Infraorder Hypsilophodontia
family Hypsilophodontidae
family Thescelosauridae
family "Muttaburrasauridae"
family Tenontosauridae

Infraorder Iguanodontia
family Dryosauridae
family Camptosauridae
family Iguanodontidae
family Hadrosauridae

Notes on the Infraorder Iguanodontia: This large group evolved from hypsilophodonts sometime during the middle Jurassic and includes most of the medium-sized and large ornithopods. Relatively rare during the Jurassic, they became the dominant herbivores of the northern (Laurasian) faunas throughout the Cretaceous. Iguanodontians form an evolutionary sequence from the relatively small and quite hypsilophodont-like dryosaurids through the medium-sized Camptosaurs to the very large (weights generally about 2 to 3 tonnes, although a few were much larger) iguanodontids and hadrosaurids.  The dryosaurs were obligatory bipeds with forelimbs too small to walk with. Like the hypsilophodonts they were lightly built, very fast runners, relying on fleetness of foot to escape carnivores lareg and small.  The camptosaurids, iguanodontids, and hadrosaurids were able to walk on either two legs or four. They probably ran on their hind-legs but moved slowly on all fours. There was also a tendency towards a broad flaring of the snout and massive dental batteries, all of which reached their extreme in the hadrosaurids or 'duck-bileld" dinosaurs, perhaps the most efficienmt and abundant of all the dinosaurian plant-eaters.

Links

Ornithopoda - Palaeos

UCMP Ornithopoda

Ornithopoda (Predentata) - Justin Tweet's Thescelosaurus site

Ornithopoda - Dinosauricon - cladogram and brief notes. Suggests that the Hypsilophodontia, are a paraphyletic sequence of ancestors to higher ornithopods, and not, as previously thought, a monophyletic sister clade of Iguanodontia.

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

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