Here we've listed those basal ornithischians which do not belong to any of the main groups of bird-hipped dinosaurs. Scelidosaurus,note Heterodontosaurus, Lesothosaurus, and (less-frequent) Scutellosaurus are the most common in dino-books; in older works you'll frequently also read the name "Fabrosaurus".
- Heterodontosaurians were originally thought ornithopods, then ancient relatives of ceratopsians and pachycephalosaurs; today they are generally regarded as very basal ornithischians. Despite their primitiveness, heterodontosaurs not only flourished in the Early Jurassic, but also managed to survive until the Late Jurassic and even the Early Cretaceous: English Echinodon lived alongside Iguanodon and Hypsilophodon! Half the length of Heterodontosaurus tucki and with small tusks only in the upper jaws, Echinodon ("hedgehog tooth") is known to science since the middle XIX century, but its classification as a heterodontosaurian has been confirmed only after the discovery of the namesake of the group (it was also briefly believed a Scutellosaurus relative in the nineties). Geranosaurus ("crane lizard") and Lycorhinus ("wolf nose") were both found in South Africa at the start of the XX century, and also were originally not classified as heterodontosaurs because Heterodontosaurus was not known yet: Lycorhinus, with its typically heterodontosaurian mammal-like dentition, was initially believed a non-dinosaurian therapsid like Cynognathus. Also South-African and Early-Jurassic, Abrictosaurus and Lanasaurus (the latter often synonimized with Lycorhinus) were found about in the same time of Heterodontosaurus; the former's name, "awake lizard", is actually ironical, because it was hypothized that Abrictosaurus underwent "hibernations" (just like what has been proposed for Lesothosaurus, but again, this is not demonstrated). Curiously for a heterodontosaur, Abrictosaurus was totally tusk-less, and because of this was once believed a possible female Heterodontosaurus (this originated from a confrontation with the modern musk-deers, whose males only bear tusks). Some important dinosaur discoveries that have been made since the 2009 regard the heterodontosaurian group. For example, Fruitadens ("Fruita's tooth" from the geological formation that preserved it) lived in the Late Jurassic North America alongside the famous jurassic Stock Dinosaurs; in opposite to the "younger" Echinodon, Fruitadens has tusks only in its lower jaw. With only two feet of length (the same size of a Microraptor), Fruitadens is currently the smallest known North American dinosaur; it and Echinodon are among the smallest bird-hipped dinosaurs ever discovered, only equalled by some marginocephalians (ceratopsians & pachycephalosaurs) like Microceratus and Wannanosaurus, and some "hypsilophodont" ornithopods.
The First Armor against the Predators: Scutellosaurus
- Scutellosaurus ("lizard with small shields", not to be confused with the near-reptile Scutosaurus) has traditionally been the most primitive thyreophoran, variably classified in the Scelidosaurids or in its own family, Scutellosaurids. Discovered only in the 1980s, Scutellosaurus lawleri was also a small bipedal animal with a similar look, but slighty bigger, longer-tailed, more robustly-built than the lesothosaur, and with longer forelimbs: some think was partially quadruped. More importantly, it had a light armor made by small bony plates placed in rows upon its torso, and a row of plates along its backbone from neck to tail: all similar to the armor of the bigger Scelidosaurus, but without the "horns" on its head. Some could say Scutellosaurus was a bit like a primitive miniature Tenontosaurus because of its very developed tail longer than the rest of the body from nose to hips (Scelidosaurus had a more normally-long tail). Like the scelidosaur, Scutellosaurus lived in Early Jurassic, but was found not in Europe like the former but in Arizona, where the popular double-crested Dilophosaurus lived: some portrayals have shown the scutellosaur as that dinosaur's prey, but this is not confirmed. If it had "feathers" or not, this is unknown: but if it had them, they were intersparse between the bony scutes that give to it its name.
At the Origins: Pisanosaurus
- Found in the last decades of the XX century, the Argentinian Pisanosaurus mertii lived in the Middle Triassic (well before Coelophysis and Plateosaurus) and shared its habitat with the alleged first theropods" Herrerasaurus & Eoraptor and many non-dinosaur reptiles such as rhynchosaurs, "thecodonts", and mammal-ancestors (all these were much more common at the time than dinosaurs, never forget this). The pisanosaur still remains the most ancient ornithischian known to science, but sadly, is known only from one incomplete fossil. It was arguably similar to Lesothosaurus in shape and size, and with no armor like the latter. One significative thing is that some Triassic non-dinosaurian archosaurs were once considered basal ornithischians as well (often put in the "fabrosaurid" assemblage): Technosaurus from Texas is one example, sometimes mentioned as "the most ancient North American ornithischian"; other two examples are Revueltosaurus and chinese Dianchungosaurus (the latter was believed a heterodontosaur). The evocative name Technosaurus comes from the Texas Tech University; interestingly, another basal ornithischian, the European Emausaurus (known only from a skull) also derives its name from an university, the German EMAU. It is usually believed in the middle between Scutellosaurus and Scelidosaurus, but some think it's a very primitive stegosaurian. Other three animals are usually considered closer to Scelidosaurus than to Scutellosaurus: Portuguese Lusitanosaurus ("lizard from Portugal") and Chinese Bienosaurus and Tatisaurus.
A Complete Key Fossil: Eocursor
- Like the basal saurischians, basal ornithischians as a whole are mostly known only since the 1960s — not counting Scelidosaurus, which has been known since the XIX century but has recently re-classified as an extremely basal ankylosaurian — and still arent well-understood. So, every recent discover could be very significative. Eocursor and Tianyulong in particular, have fairly gained much consideration in scientific field because of their objective importance. Found in 2007, Eocursor parvus (small dawn-runner) was discovered in South Africa like Heterodontosaurus and Lesothosaurus, and its name recalls that of the famous Eoraptor (dawn robber). Its relevance is due to the fact that its the only Triassic ornithischian known so far from a complete skeleton (while the remain of the even earlier Pisanosaurus is only partial); this gives us precious information about the deepest ornithischian roots, and also could better explain the relationship between bird-hipped dinosaurs and the saurischians. According to the most accepted classification, ornithischians are divided in two main lineages: Thyreophorans and Cerapods. The former are Stegosaurs+Ankylosaurs+some basal forms (Scutellosaurus, Emausaurus, and maybe Lesothosaurus). Cerapods include almost all the other ornithischians, furthermorely divided in Ornithopods (duckbills, Iguanodon, Hypsilophodon etc) and Marginocephalians (ceratopsians+pachycephalosaurs). Indeed, Cerapods is just a Portmanteau made of Cera(topsian) and (Ornitho)pod.
First-Known Feathered Ornithischian: Tianyulong
- Found even more recently, in year 2014, Kulindadromeus ("Kulinda's runner") from Russia was also a very basal ornithopod like Eocursor, with tracks of proto-feathers left. About Tianyulong confuciusi: this is a heterodontosaurid from the Late Jurassic found in 2009 in the same Liaoning site from which the Jurassic near-bird Anchiornis was discovered. Tianyulong, like the latter, has preserved some sort of proto-feathers around its body. The thing is, this is the first time that unequivocally feather-like structures have been found in a non-theropod dinosaur (not counting the quills of Psittacosaurus found in 2001). See the useful notes about dinosaurs in general to understand the revolutionary implications of this discovery.