By far the dominant herbivorous component of Australia's dinofauna is the clade Euclasauria, an extremely derived, regionally endemic group of ornithopods. Euclasauria consists of about 75 species in 4 families, of which 59 are found in Australia. Other euclasaur representatives can be found throughout New Guinea and Indonesia.
All extant euclasaurs are obligate quadrupeds (although some can rear on their hind limbs) with a 3 or 4-toed manus. Digestion of tough plants is aided by a specially sacculated stomach ("dinorumen") which, uniquely among vertebrates, seems to rely primarily on symbiotic protozoa to digest fibrous plant matter (other digestive systems depend on bacteria). Uniquely for archosaurs, Euclasaurs are ovoviviparous, giving birth to between 1 to 4 offspring (mostly 2). The leathery-shelled eggs are retained in a cloacal brood pouch until they hatch. The heads of many species are decorated with horns or casques which may be used to distinguish between sexes.
The Cretaceous ancestry of the Euclasauria can be traced to small, basal euornithopods from South-Polar Gondwana (Atlascopcosaurus, Qantassaurus), which possessed a peculiar large ridge on their teeth (which has now been lost in all but the most primitive euclasaurs). These forms, dubbed "antarctornithopods" persisted into the early Cenozoic, radiating into a number of lineages in the Eocene, including the precursors of the Euclasauria, Viriosauria and Rhynchoraptoria. The earliest true euclasaurs appear in the Miocene deposits of Riversleigh, but it was not until the early Pliocene that the group became truly prominent, undergoing an diversification event that has been described as an "evolutionary tacnuke". By the end of the Pliocene, the euclasaurs had developed into a myriad of bizarre herbivores, in doing so, edging out nearly all other ornithischians.
The only extant euclasaur family to retain the primitive ridged grinding teeth of the ancient antarctornithopods, proeuclasauroids are small, gracile herbivores with a range that spans from Tasmania to Borneo. Most of these species are obligate quadrupeds, but one or two smaller species spend much of their time on their hind legs.
Proeuclasaurs are most common in the forests of southern and eastern Australia and on the island of Tasmania. In the north and interior, these deer-like herbivores are replaced by chlorosaurs and iguanodontians, respectively, but once were more widespread.
Common Rainbow Brush-runner (Mossmania sp.)
A diminutive denizen of the rainforests of the east coast, the common rainbow brush-runner feeds on leaves and fruits of a wide variety of plants as well as grasses on the forest edge. An extremely alert and "jittery" animal, this euclasaur is the most widespread member of the Mossmania calura-species complex. The true M. calura is now known to be restricted to Fraser Island.
Long-horned Euclasaur (Ceratodromeus leucopus)
The long-horned euclasaur (Ceratodromeus leucopus) is a characteristic species of the savannah and woodlands of southeastern Australia, and lives in huge nomadic herds.
The chlorosaurids are small denizens of the Papua-New Guinea that migrated from Australia early in their history. While some are still present in northern Australia, chlorosaurids are increasingly replaced by proeuclasauroids further south.
Chlorosaurids are generally small, the largest, Chlorosaurus ornatissimus, reaching 3 meters in length. They are swift and lightly-built runners, similar to the proeuclasauroids in many respects. The few notable difference between the two clades include the chlorosaurs' tendency to grow large and elaborate cranial ornamentation. These crests or casques are not bone, as is the case with some other euclasaurs, but hollow keratin structures, usually in the form of a lambeosaur-like tube extending off the forehead. Chlorosaurids are also the only group of euclasaurs that has gone back to bipedalism. While some chlorosaurids are quadripedal, species of the genus Parachlorosaurus spend their entire adult lives on their hind legs.
Chlorosaurids are the worst known family of euclasaurs, with many species only now coming to light. Their habits are still poorly known, and much of their species count my simply be color variation in just a few true species. Thus, there may be as many as 7, or as few as three known species of chlorosaur, distributed between 3 genera. Chlorosaurs range from the northern tropical forests of Australia to Papua-New Guinea. Un-authenticated reports allege to chlorosaur species on the Moluccan islands, Timor islands and in the Philippines.
Ornate Green Euclasaur (Chlorosaurus ornatissimus)
Despite of the name (Chlorosaurus, means "Green saurian") Chlorosaurinae is only a clade, meaning that not all its belonging species are in fact, green, and therefore proved to be related by DNA analysis not coloration. The Ornate green euclasaur, Chlorosaurus ornatissimus is one such example.
Splashback Euclasaur (Parachlorosaurus viduatus)
The Splashback Euclasaur, Parachlorosaurus viduatus, is a blue-black species found in Timor and the Lesser Sundas Islands, comprising two races which some consider to be subspecies: The Sundasian Splashback Euclasaur (Parachlorosaurus viduatus viduatus), from the Lesser Sundas and the Timorian Splashback Euclarsaur (Parachlorosaurus viduatus timorensis) from the Timor Island. This is an elusive species which often remains hidden in the vegetation. A series of blue splashes, starting at the base of the tail is a shared trait for both races, but the nominate race carries only one blue stripe on the flanks while timorensis carries two.
Euclasaurids are the most common, and the largest, members of clade Euclasauria. These massive herbivores echo the hadrosaurs of Africa and Laurasia, and possess many convergent features with this group, including a quadripedal stance, short, deep tails, and horse-like muzzles tipped by flattened beaks.
Euclasaurids fill all of the large grazer and low-browser niches on Australia. Most are quite large, the four-ton highcrest euclasaur being an average size for this group.
Highcrest Euclasaur (Euclarsaurus ornatus)
A giant euclasaur species of southwestern Australia, the highcrest euclasaur is an animal of coastal woodland, scrub and heath, infrequently venturing into the more arid inland areas. Unlike the great euclasaur, the highcrest rarely herds and usually lives in mated pairs or small family groups.
This was the first euclasaur species to be formally described, and was so named because the holotype and paratypes were gunned down...I mean collected, at a locality corresponding in our world to the town of Eucla, near the Western-South Australian border.
Great Euclasaur (Euclarsaurus ingens)
By far the largest land animal on the continent, small herds of these behemoths can be found in savannah and open woodland habitats throughout eastern and northern Australia (a closely related species is found in the southwest). Not a fussy-feeder, great euclasaurs will happily munch on grasses and a wide variety of low-foliage.
Magnificent Hexacorn (Hexacornis magnificus)
The magnificent hexacorn (Hexacornis magnificus) is a spectacular swamp-dweller that feeds on sedges and aquatic grasses as well as browsing on p-Pandanus leaves. During the Pleistocene, hexacorns could be found throughout northern and eastern Australia today they are restricted to the wetlands of Kakadu and Arnhem Land, this applies to the subspecies in the area, most notably Hexacornis magnificus arnhemensis. Other subspecies are found on Papua, most notably "Hexacornis magnificus papuaensis".
Duohorn (Bicornis benemattii)
The duohorn (Bicornis benemattii) is a relatively rare eucalsaur, found only in the arid grasslands of Western Australia. Genetic evidence suggests and internal anatomy suggest that the duohorn's closest relative are the hexacorns (genus Hexacornis), but if so, these grazers have diverged strongly from their moose-like cousins.
Duohorns are grazers, rather like the more distantly related genus Euclasaurus of southern an eastern Australia. Their beaks, which are blunt but not squared, are capable of cropping a wide range of vegetation, which is then digested with the aid of the duohorn's euclasaurian digestive track. Duohorns are capable of tackling the toughest grasses, the spiniest acacias, and even the formidable dontgothere shurbs. It is not unknown for these hardy animals to venture into sclerophyll forests, where they mow over bushes and young trees.
The two immense horns that give the duohorn its name rise up from the postorbitals just behind the eye sockets to form an impressive capital-V shape. These horns are mostly keratin, but they are still quite heavy, held aloft by powerful muslces anchored to enlarged neural spines over a duohorn's shoulder-blades. Unlike the hexacorns, which use their horns as principally as sexual symbols, the cranial structures of the duohorns are intended for a far more utilitarian purpose. A mature duohorn possesses a powerful defensive weapon on its head, a weapon it has no compunctions against using. Attackting rhynchoraptors can be maimed or killed by a sideways swipe of a duohorn's head, and specbiologists live in constant fear of these short-tempered creatures.
Baluong (Alloceros brontogenus)
This species of Euclarsaur that was though to believed to be extinct, but was recently found roaming Eastern Australia. As of now not much is known about it at the moment, but more research will be conducted in the future. However, what is known is that they travel in large family herds.
Red-crested Tanamisaur(Tanamisaurus erythronasus)
With only a single genus and three species to its name, the strange clade Tanamisauridae is a remnant from a once vibrant diversity of euclasaurs, killed during the Ice Age when vast tracks of Australian forest turned to desert scrub. Tanamisaurids probably evolved as high-level browsers, similar to the South American pseudosauropods, but the drying of Australia robbed them of their habitat. Today, tanamisaurs, most notably the red-crested tanamisaur (Tanamisaurus erythronasus) live on the edges of Australia's great interior desert, eating whatever vegetation they can find, and storing excess protein in a camel-like, fatty hump on their backs.
The tanamisaurs are animals beautifully adapted to life in the arid interior and are widely distributed in the deserts and semi-deserts of Central and Western Australia. The anterior hump is a water-reservoir whilst the posterior one consists mostly of fat. During sandstorms, the slit-like nostrils can be closed whilst a thick, translucent membrane protects the eyes.
"Managed to get a snap of an old bull Red-crested Tanamisaur whilst driving across the Nullabor. You see heaps of female/juvenile herds around the place but those big males are lone wanderers...real thrill to get up close to one! Was the start of the dry season...but there was still heaps of greenery around the place thanks to an unusually good rain. Still, this guy was already stuffing his face, his humps were already bulging in anticipation of the coming hard times. Smart, probably how he managed to live so long.
The mating season was long over but he still had quite a bit of colour in that crest of his. He just stood there, chewing his cud while I approached him. These animals look so spindly from a distance that you don't realise just how big they are until you're up close. He snorted in annoyance as I took the shot, or maybe it was because of all those flies buzzing around his nostrils that he got so ticked off? He turned to the north and started walking. As a blur on the horizon, he stopped and continued feeding..."
- Brian Choo, João Boto, and Daniel Bensen
,=Mossmania calura (Common rainbow brush-runner) ,=Proeuclasauria=| | `=Ceratodromeus leucopus (Long-horned euclasaur) ,=| | | ,=Chlorosaurus ornatissimus (Ornate green euclasaur) | `=Chlorosauria=| | `=Parachlorosaurus viduatus (Splashback euclasaur)
| ,=Euclasaurus ornatus (Highcrest euclasaur) | ,=| | | `=Euclasaurus ingens (Great euclasaur) | ,=Euclasauridae| | | | ,=Bicornis benemattii (Duohorn) | | `=| | | `=Hexacornis magnificus (Magnificent hexacorn) `=|
`=Tanamisauridae=Tanamisaurus erythronasus (Red-crested tanamisaur)