Among non-hadrosaur/non-''Iguanodon'' ornithopods, the ones you've more chances to see in media are: ''Hypsilophodon'' (the prototype of the "hypsilophodonts" aka small-slender members of the group); ''Camptosaurus'' & ''Dryosaurus'' (the two iconic ornithopods from the Late Jurassic): ''Tenontosaurus'' (apparently in the middle between an ''Iguanodon'' and a ''Hypsilophodon''); and ''Ouranosaurus'' (traditionally considered an "iguanodont" but actually closer to hadrosaurs). Among the other examples, the Australian ''Muttaburrasaurus'' and ''Leaellynasaura'' [[note]]The latter, according to recent research, could not be a proper ornithopod however.[[/note]] were portrayed in 1999 by WalkingWithDinosaurs, while ''Orodromeus'' and ''Thescelosaurus'' have had notable ScienceMarchesOn stories.

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'''When dinosaurs went down trees:''' ''[[http://en.wikipedia.org/wiki/Hypsilophodon Hypsilophodon]]''

When we think about small bipedal dinosaurs, our mind authomatically comes to guys like the “raptors”, the “compies”, or the ornithomimids. But there were also several ornithopods which shared an analogue body-shape with the latter; even though they are usually ignored by film-makers. The most iconic of them has always been ''Hypsilophodon''.

One of the first dinosaurs discovered (middle XIX century), lived in Europe 130-125 million years ago together with its gigantic relative ''Iguanodon'', and was originally considered the latter’s juvenile specimen. Unusually for such a small animal, dozens complete individuals have been found, and this also explains its historical role as the stock small ornithopod. Even though most remains come from England (especially the Isle of Wight), some uncertain remains come from North America. A very small dinosaur, 2 m long or less, the size of a dog, ''Hypsilophodon'' is easily distinguishable from theropods by its horny beak on the lower jaw, small mouth-opening typical of ornithischians, large grinding teeth at the bottom of the mouth hidden by cheeks in the living animal, hands with five digits (coelurosaurs never have more than three fingers), and a more round belly to contain the typical large gut of a herbivore.

''Hypsilophodon'' is nicknamed “the gazelle dinosaur”. The comparison works very well: it was a graceful, harmless, wide-eyed biped that escaped predators thanks to its agile legs well adapted for high-speed runs: it was certainly one of the fastest-running dinosaurs. If alive today, it would probably appear one of the cutest-looking dinos, maybe even suitable as a good [[TeamPet household pet]]. But before the 1970s, ''Hypsilophodon'' used to be depicted as a tree-climbing animal, vaguely similar to a large, long-legged, spike-less iguana, and long depicted in this way in books, 3D models, and perhaps even fiction. Few other dinosaurs have had such a great ScienceMarchesOn change during their story.

The traditional prototype of the eponymous "hypsilophodonts" (small/slender non-hadrosaurian ornithopods), ''Hypsilophodon'' is classically countered against ''Iguanodon'', which in turn is the classic prototype of the the “iguanodonts” (large/heavy non-hadrosaurian ornithopods). [[ScienceMarchesOn Now scientists have found]] “hypsilophodonts” is an artificial assemblage including the most basal ornithopods, while “iguanodonts” now indicates a natural group including not only the most ''Iguanodon''-like animals but also duckbills, pre-duckbills and also some traditional “hypsilophodontians” (see below).

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'''The Jurassic antelopes:''' ''[[http://en.wikipedia.org/wiki/Camptosaurus Camptosaurus]]'' & ''[[http://en.wikipedia.org/wiki/Dryosaurus Dryosaurus]]''

Let’s face it: it’s RuleOfCool that undisputedly dominates when coping with dinosaurs. ''Camptosaurus'' is the perfect example. In spite of being one of the most abundant dinosaurs in fossil record, and also one of the most common dinosaurs in museums around the world… when was the last time you’ve you watched it in recent documentaries? The problem is, ''Camptosaurus'' lived ''just'' alongside [[StockDinosaurs dino-stars]] like these: ''Apatosaurus'', ''Diplodocus'', ''Brachiosaurus'', ''Stegosaurus''... and ''Allosaurus''. Thus, it could have shown up in ''WalkingWithDinosaurs'', ''Ballad of Big Al'' or even ''WhenDinosaursRoamedAmerica''. But, as it seems, its very generic appearance was judiced [[ViewersAreMorons too incospicuous to capture the watchers’ interest]].

On the other hand, the other well-known Late Jurassic ornithopod, ''Dryosaurus'', despite being even less-conspicuous than ''Camptosaurus'', has received a better treatment showing up in all the three documentaries above, though with very minor roles (in one case, it serves only to give a prey to ''Allosaurus'').

''Camptosaurus'' was similar to ''[[StockDinosaurs Iguanodon]]'' but smaller (5-7 m long) and with mere hints of thumbspikes. [[note]]Some portrayals show ''Camptosaurus'' totally spike-less or with fully-developed ''Iguanodon''-like spikes, both incorrect.[[/note]] This because was one of the most primitive large-sized ornithopods, and a possible ancestor of ''Iguanodon'' and, indirectly, hadrosaurs. In the Jurassic world still dominated by sauropods, camptosaurids and stegosaurs were the only big ornithischians which were successful, anticipating the great diversity bird-hipped dinosaurs reached later in the Cretaceous. ''Dryosaurus'' was much smaller than ''Camptosaurus'' and more similar to a ''Hypsilophodon'' in shape, being totally bipedal. Compared with ''Hypsilophodon'', the dryosaur was larger (3-4 m long), slightly more robust, and with a toothless beak. Nonetheless, ''Dryosaurus'' was a basal iguanodont, closer to ''Iguanodon'' than to ''Hypsilophodon''.

Both discovered during the Bone Wars, ''Camptosaurus'' and ''Dryosaurus'' have been found in the USA. Some close relatives known from Europe include the camptosaurid ''Draconyx'' and the dryosaurid ''Valdosaurus''. Specimens once referred to ''Dryosaurus'' have also been discovered in Africa - more precisely in Tendaguru (together with ''Giraffatitan'' and ''Kentrosaurus''); they have been recently re-classified as ''Dysalotosaurus''.

''Camptosaurus'' and ''Dryosaurus'' are very frequently portrayed in dinosaur books, especially ''Camptosaurus''; here is typically shown as one of the favorite prey of ''Allosaurus'', a concept that is almost certainly [[TruthInTelevision Truth In Books]]. Indeed, in North American placements, camptosaurids and dryosaurids were respectively the “wildebeest” and the “Thompson’s gazelles” of their fauna, that escaped their reptilian “lions” and “hyenas” (carnosaurs and ceratosaurs) by running fast on two legs. Dryosaurids, being smaller and more manouvreable, were arguably less-easy prey to catch than camptosaurids, at least for an adult ''Allosaurus'' - a fully-grown, 2-ton ''Camptosaurus'' was surely a difficult task for young carnosaurs and maybe adult ceratosaurs too.

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'''Hearts of stone and spiral nests:''' ''[[http://en.wikipedia.org/wiki/Thescelosaurus Thescelosaurus]]'' & ''[[http://en.wikipedia.org/wiki/Orodromeus Orodromeus]]''

Hypsilophodon-like animals existed also in Late Cretaceous, but tend to be overshadowed by the spectacular ornithischians of their period (hadrosaurs, ceratopsians etc.). In North-America, while duckbills ruled the “wildebeest” role, the “gazelle” one was mainly played by ''Thescelosaurus''. 3-4 m long and rather similar to ''Dryosaurus'', it was not a basal iguanodont however unlike the latter. One peculiar trait are the small bony plates on its back, maybe placed under the skin and not-visible in the living animal.

''Thescelosaurus'' is the animal from which the controversial “fossilized heart” comes from, which is almost certainly a fossilization artifact: that is, a piece of stone found in one specimen, which casually resembles a heart. Discovered in year 2000, this stony concretion was celebrated as the proof of “warm-bloodedness” among dinosaurs, because it seemingly showed a four-chambered heart just like bird and mammals and unlike most modern reptiles -- crocodilians have four-chambered hearts, but their ancestors could have been warm-blooded as hypothized in the late 2000s.

Other “hypsilophodontians” from Late Cretaceous North America were ''[[http://en.wikipedia.org/wiki/Parksosaurus Parksosaurus]]'' and ''Orodromeus''. Both were smaller than ''Thescelosaurus'', and lived slightly earlier. ''Orodromeus'' was once thought to be the source of some small nests full of eggs containing fossilized embryos, discovered in 1988 just next to the more famous ''Maiasaura'' ones. [[ScienceMarchesOn We now know]] that those eggs were from the theropod ''Troodon'' instead. The ironical thing is, fossils of troodonts were discovered as well around those putative ''Orodromeus'' nests, but it was thought that they were ''actually preying on Orodromeus nestlings'': an astonishingly similar story to the “[[StockDinosaurs Oviraptor robbing Protoceratops' eggs]]”.

Found in 2007, its relative ''[[http://en.wikipedia.org/wiki/Oryctodromeus Oryctodromeus]]''
lived quite a bit earlier than the similar-named ''Orodromeus'', but has also shown the first proof of digging behavior among non-avian dinosaurs: its skeleton has been found inside a fossilized burrow. Another relative, ''Zephyrosaurus'', lived even earlier in the Early Cretaceous alongside ''Deinonychus'' and was possibly its prey.


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'''Duck-billed spinosaur:''' ''[[http://en.wikipedia.org/wiki/Ouranosaurus Ouranosaurus]]''

Here’s one of the best dinosaurian MixAndMatchCritter examples: ''Ouranosaurus''. This medium sized (7 m long) ornithopod looked like a cross between other more familiar dinosaurs. Flat-billed head like ''Anatosaurus''; thumbspikes like ''Iguanodon''; and, above all, a wide spinal crest on its back, similar to ''Spinosaurus'' but less tall and extending from the shoulders down to the tip of the tail.

Named in the 1970s, ''Ouranosaurus'' lived in Cretaceous Sahara like ''Spinosaurus'', and the latter has often been shown as the predator of the former - [[AnachronismStew this is actually a mistake]], because ''Ouranosaurus'' lived 15 million years before "Spino". Nevertheless, its one documentary appearance in "Planet Dinosaur" showed the two living at the same time. Today, some scientists argue that ''Ouranosaurus'' had a fleshy hump instead of a “sail”, because its vertebrae are similar to those of modern bison. But others say that comparing dinosaurs with modern big mammals is not correct, since these are two completely distinct zoological groups.

''Ouranosaurus'' is the most well-known among those middle-ways between ''Iguanodon'' and hadrosaurs called “basal hadrosauroids”, and was closer to duckbills than to ''Iguanodon''. Unlike true hadrosaurs (whose teeth were crammed in "batteries") the ouranosaur had teeth placed in one single line on each half-jaw -- the primitive condition of the non-hadrosaur iguanodonts. Among the other possible pre-hadrosaurs, other than ''Altirhinus'' (see below) and ''Probactrosaurus'', is also worth of mention ''[[http://en.wikipedia.org/wiki/Protohadros Protohadros]]'' and ''[[http://en.wikipedia.org/wiki/Eolambia Eolambia]]'', both discovered in 1998 in the USA. The former was initially considered the earliest hadrosaur (its name just means “the first hadrosaur”); the latter received a similar treatment, initially described as the first ancestor of crested hadrosaurs (''Eolambia'' means "dawn lambeosaurine"). On the other hand, the heavily-built ''[[http://en.wikipedia.org/wiki/Lurdusaurus Lurdusaurus]]'' seems very closely-related to ''Iguanodon'', even though shared its habitat with ''Ouranosaurus'' in North Africa. Interestingly, ''Lurdusaurus'' seems showing adaptations for a semi-aquatic lifestyle, which is unusual for ornithischian dinosaurs. [[note]]This hyp was also made for another ornithischian, the basal ceratopsian ''Koreaceratops'': found only in 2012, its describer believed it was actually a ''marine'' dinosaur![[/note]]

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'''Stock Fodder:''' ''[[http://en.wikipedia.org/wiki/Tenontosaurus Tenontosaurus]]''

One of the most iconic scenes in those paleo-artistic works made in full Dino-Renaissance was a fight between a whole pack of ''Deinonychus'' and a much heavier ornithopod; even though ''Iguanodon'' was often chosen in this role, the most classic choice has been another relative, ''Tenontosaurus''.

This was one of the most basal known iguanodontians, an Early Cretaceous animal similar in size to the Jurassic ''Camptosaurus'' but totally devoid of thumbspikes (it was once considered an overgrown "hypsilophodont") and with a much longer tail, ''twice'' the length of the rest of its body. First found in the 1970s in Montana, its first skeleton was surrounded by several ''Deinonychus'' skeletons; it was just this detail that made John Ostrom to think about these predators as wolf-like pack-hunters capable to bring down giant preys with their agility and their sickle-claws. Even though in an indirect way, ''Tenontosaurus'' has thus given a strong contribute to the public image of dinosaurs.

In these struggles, ''Tenontosaurus'' is usually shown swinging its enormous tail and hitting some “raptors” to death, before being killed and eaten by the remaining ''Deinonychus''. The Tenontosaur-Deinonychus battle is more justified than the Iguanodon-Deinonychus one, both because the former has at least one possible proof, and because an adult ''Iguanodon'' would have weighed ''eighty times more than Deinonychus'' (see RaptorAttack). Some scientists, however, have recently suggested that the carnivores simply ate the carcass of the ''Tenontosaurus'' they found already dead. The presence of their skeletons around the herbivore could be explained if some “raptors” fought each other to the point that some ended killed by their own companions.

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'''Land Down Under dinosaurs:''' ''[[http://en.wikipedia.org/wiki/Leaellynasaura Leaellynasaura]]'' & ''[[http://en.wikipedia.org/wiki/Muttaburrasaurus Muttaburrasaurus]]''

If you’ve seen the fifth episode of WalkingWithDinosaurs, you’ll already have the idea what we’re talking about. If dinosaur names are often thought bizarre-sounding, these ones certainly do match the commonplace very well. ''Muttaburrasaurus'' is called from the small town of Muttaburra in Queensland, Australia, where its only skeleton was found in 1980. ''Leaellynasaura'' was named after the daughter of its discoverers, Leaellyn: [[note]] Another little-known australian dinosaur, ''Timimus'', was named after Leaellyn's brother, Tim. It has ''mimus'' at the end because was originally thought an ornithomimosaur.[[/note]] hence its feminine suffix ''saura'' - just like ''[[StockDinosaurs Maiasaura]]'' which means “good-mother lizard”. Together with the much simpler-named but equally bizarre-sounding ankylosaur ''Minmi'', these are the most well-known Aussie Dinos.

Similar but smaller than ''Iguanodon'' (about the same size of ''Camptosaurus'', ''Ouranosaurus'' or ''Tenontosaurus''), ''Muttaburrasaurus'' is easy to tell apart from its relatives thanks to its prominent nose, similar to other ornithopods but more bulbous. We don't know if it had thumbspikes: being more basal than the almost-spikeless ''Camptosaurus'', this is unlikely, but it is traditionally shown with them in drawings. Found in 1989, ''Leaellynasaura'' was a tiny (less than 1 m long) bipedal animal similar to ''Hypsilophodon'', but with the possibility of having a tail 3 times longer that its own body. Once considered an “hypsilophodontian”, even its ornithopod status is disputed today, and is now generally regarded as a more basal ornithischian.

The discover of these dinosaurs in the 1980s made sensation in Australia, because very few dinosaurs were known before in the LandDownUnder, all fragmentary. ''Muttaburrasaurus'' still is one of the most complete dinosaurs found there; on the other hand, ''Leaellynasaura'' ‘s only skeleton is very incomplete, but its importance was due to having contributed to enforce the “warm-blooded dinosaurs” hypothesis even more. In Early Cretaceous, Australia was not the temperate/tropical/desertic country we know today, but a colder world with warm summers but cold winters - because was much closer to the South Pole. How could such a small, clearly non-migratory animal manage to survive that icy winter? The only explanation was: ''Leaellynasaura'' was warm-blooded. Furthermore, its unusually big eyes could have been used to see throughout the darkness of the polar winter. All these arguments have been discussed in WalkingWithDinosaurs, in which a family of ''Leaellynasaura'' makes the main characters. The show also portrayed ''Muttaburrasaurus'' and added to it speculative nasal sacs to make loud sounds, but we don't have direct evidence for this.

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'''Iguanodons everywhere?:''' ''[[http://en.wikipedia.org/wiki/Altirhinus Altirhinus]]'' & ''[[http://en.wikipedia.org/wiki/Mantellisaurus Mantellisaurus]]''

Since its first discovery made in the first decades of the XIX Century, ''Iguanodon'' remains have been found everywhere from Africa to Mongolia, Europe and North America. [[WalkingWithDinosaurs Chased By Dinosaurs]] added some sorta iguanodons even in South American settings - even though some iguanodontians ''are'' known from South America, they were much smaller. ScienceMarchesOn however, and now many of these ''Iguanodon'' species have been reclassified in other genera.

Several from Europe have been created as an homage to some of the greatest XIX century paleontologists (at the time, dinosaur remains were mainly from ''Iguanodon''s). So we have ''Mantellisaurus'' from Gideon Mantell (''Iguanodon''’s TropeNamer), ''Owenodon'' from Richard Owen (dinosaurs’ TropeNamer), and ''Dollodon'' from Louis Dollo (the guy who described the famous iguanodonts found in the “Dinosaur Mine” in Belgium as erect bipedal beasts. [[note]]However, ''Dollodon'' is very likely the same as ''Mantellisaurus''. Another former ''Iguanodon'' species has been renamed ''Huxleysaurus'' (after Thomas Henry Huxley, supporter of Darwin's theory of evolution), but this name is unofficial at present.[[/note]] Other Europeans were named for their unique physical characteristics, such as ''Hypselospinus'' ("tall spines") and ''Barilium'' ("heavy hips"). The North American ''Iguanodon'' was renamed ''Dakotadon'' after the state it was found in. A similar fate befell another South Dakotan iguanodont: ''Osmakasaurus'', from the same rock unit as ''[[http://en.wikipedia.org/wiki/Dakotadon Dakotadon]]''
, was originally named as a species of ''Camptosaurus''.

Finally, the Mongolian specimen "Iguanodon orientalis" has been renamed ''Altirhinus''. As with most former ''Iguanodon'' specimens, ''Altirhinus'' was actually closer to hadrosaurs than to ''Iguanodon''. Indeed its name, “high nose”, was given from its humped nose similar to the duckbill ''Gryposaurus''. Interesting that Kron (the villainous ''Iguanodon'' in {{Dinosaur}}) has a hump-nose that could mean he’s actually an ''Altirhinus''.

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'''More primitive guys:''' ''[[http://en.wikipedia.org/wiki/Rhabdodon Rhabdodon]]'' & ''[[http://en.wikipedia.org/wiki/Yandusaurus Yandusaurus]]''

As a whole, non-hadrosaurian ornithopods have been found everywhere. Almost all the main dinosaurian faunas had at least one known ornithopod: even the famous Late Cretaceous islets which were where today is Central Europe. ''Rhabdodon'' was a sort of “dwarf iguanodont”, a primitive spike-less iguanodontian analogue to the earlier ''Dryosaurus'' and ''Tenontosaurus''; it was a late-surviving form which managed to reach the K/T extinction event just thanks to its insulation and absence of competition from the much more evolved hadrosaurs. But wait: some hadrosaurs are ''actually'' known as well from that habitat, such as ''Telmatosaurus''; only, they too were small and primitive. From the same fauna are the close ''Rhabdodon'' relatives ''Mochlodon'' and ''Zalmoxes''. On the other hand, ''[[http://en.wikipedia.org/wiki/Callovosaurus Callovosaurus]]'' (found in England) comes from a far more ancient period; living in the Middle Jurassic, it was one of the most ancient iguanodontians known, and is more closely related to ''Dryosaurus''.

An even more primitive ornithopod from the same period was the Chinese “hypsilophodont” ''Yandusaurus'', perhaps the most basal ornithopod known to science. On the other hand, other “hypsies” from the same fauna were probably too primitive to be real ornithopods: the most scientifically-known is ''[[http://en.wikipedia.org/wiki/Agilisaurus Agilisaurus]]'', others are ''Xiaosaurus'', ''Gongbusaurus'' and former ''Yandusaurus'' species ''Hexinlusaurus''. From Early Cretaceous China comes the enigmatic true-ornithopod ''[[http://en.wikipedia.org/wiki/Jeholosaurus Jeholosaurus]]'', whose pointed frontal teeth seem indicating an omnivorous diet.

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'''An enduring rivarly:''' ''[[http://en.wikipedia.org/wiki/Othnielosaurus Othnielosaurus]]'' & ''[[http://en.wikipedia.org/wiki/Drinker_(dinosaur) Drinker]]''

Returning for a moment in Late Jurassic USA, other than ''Camptosaurus'' the Wildebeest and ''Dryosaurus'' the Gazelle, there was also ''Othnielosaurus'' the Dik-Dik, a very small animal with a very convoluted ScienceMarchesOn story. It was described in 1977 as ''[[http://en.wikipedia.org/wiki/Othnielia Othnielia]]'' (this is the name usually heard in docu-media), and renamed more recently because its type material was not diagnostic. Both curious names derive from [[http://en.wikipedia.org/wiki/Othniel_Charles_Marsh Othniel Charles Marsh]], one of the two scientists who “fought” the Bone-Wars in the XIX century. As it seems, its notorious rivalry with [[http://en.wikipedia.org/wiki/Edward_Drinker_Cope Edward Drinker Cope]] has lasted until today, with another similar animal from the same habitat named ''Drinker'' in 1990 out of spite!

To complicate the matter, we also have ''[[http://en.wikipedia.org/wiki/Nanosaurus Nanosaurus]]'' and ''[[http://en.wikipedia.org/wiki/Laosaurus Laosaurus]]''. Discovered during Cope’s and Marsh’s “war”, ''Nanosaurus'' was very commonly-portrayed in old textbooks for having detained the record of “the smallest North-American dinosaur” for almost a century (its name simply means “dwarf lizard”). But today it might not even be a valid name. Today, the record pertains to a tiny heterodontosaurid found only in 2009, ''Fruitadens'' (see in another page). The very fragmentary ''Laosaurus'' (described in USA in the same period of ''Nanosaurus'') has been involved in this taxonomic tangle as well.

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'''Icy amnesia:''' The "Antarctic hypsilophodont"

Finally, let’s not forget the “Mysterious Polar Dino”. In year 1987, just one year after the ankylosaur ''Antarctopelta'', the second Antarctic dinosaur was found, described as a “polar 'hypsilophodont'”; the thing is, it has had an even worse fate than the ankylosaur itself. At least, after 20 years of waiting, the latter ''has'' received a name; the poor polar "hypsy" ''has yet to wait a formal naming and description'', and sadly seems to be almost forgotten today.

Partially compensating, several small bipedal ornithischians have been then discovered in other southern continents, the best-known being ''Leaellynasaura''. It was found in 1989 in Australia along with the single lower jaw of the larger ''[[http://en.wikipedia.org/wiki/Atlascopcosaurus Atlascopcosaurus]]'' (so-called from the Atlas-Copco Corporation that funded its excavation). Today, the most-complete Australian "hypsilophodont" is ''[[http://en.wikipedia.org/wiki/Qantassaurus Qantassaurus]]'' (its name is a homage to Qantas, the LandDownUnder airlines). However, there's another relative discovered in Australia at the start of the XX century, but is known only from a femur: ''Fulgurotherium'' (the "lightening beast")

About South American discoveries, apart from the enigmatic ''Loncosaurus'' (found as well in the early XX century but known from a single femur), there are few non-hadrosaur ornithopods found in the 2000s, the largest one being the 6 m long ''Macrogryphosaurus''. Curiously, one small South American ornithopod described in 1996 [[FollowTheLeader has got]] a feminine name reminescent of ''Leaellynasaura'', ''[[http://en.wikipedia.org/wiki/Gasparinisaura Gasparinisaura]]''. Since that other small ornithischians around the world have received the suffix "-saura", for example "Bugenasaura" (now regarded as a synonym of ''Thescelosaurus'') and, last example, ''[[http://en.wikipedia.org/wiki/Trinisaura Trinisaura]]'', found in Antarctica in the earliest part of 2013 (this one has immediately received a name). Well, [[TheUnfairSex Unfair Sex]] -related names do fit better for [[AnimalMotifs these graceful “gazelle dinos”]] rather than the BadAss -looking ([[AnimalMotifs and very masculine]]) ankylosaurs...