A Herbivore with Fangs!
Here we've listed those basal ornithischians which do not belong to any of the main groups of bird-hipped dinosaurs. Scelidosaurus, Heterodontosaurus (its skull is portrayed in the image), Lesothosaurus, and (less-frequent) Scutellosaurus are the most common in dino-books; in older works you'll frequently also read the name "Fabrosaurus".
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Non-Stock Basal Ornithischians
Tiny Tusked Critters: Echinodon
& Fruitadens
- 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). 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 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 equaled by some marginocephalians (ceratopsians & pachycephalosaurs) like Microceratus and Wannanosaurus, and some "hypsilophodont" ornithopods.
The Tuskless: Abrictosaurus
- Also South-African and Early-Jurassic, Abrictosaurus and Lanasaurus (the latter often synonymized with Lycorhinus below) were found about in the same time of Heterodontosaurus; the former's name, "awake lizard", is actually ironical, because it was hypothesized that Abrictosaurus underwent "hibernations" (just like what has been proposed for Lesothosaurus, but again, this is not demonstrated). Curiously for a heterodontosaur, Abrictosaurus was believed totally tusk-less (it actually had four tiny "tusks", but much smaller than the ones of Heterodontosaurus), and because of this was once believed a possible female Heterodontosaurus — this originated from a confrontation with the modern musk-deer, whose males only bear long tusks visible when the mouth is closed. Geranosaurus ("crane lizard") and Lycorhinus ("wolf nose") were both found in South Africa at the start of the XX century, and 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.
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 was believed the most ancient ornithischian known to science, but sadly, is known only from one incomplete fossil, and now is considered only a dinosaur-like archosaur, more precisely a dinosauromorph like Lagosuchus. Pisanosaurus was nonetheless similar to Lesothosaurus in shape and size by convergent evolution.
Dinosaur or Not?: Technosaurus
- 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 (actually related with the pseodosuchians named aetosaurs) and Chinese Dianchungosaurus (the latter was believed a heterodontosaur and was also informally called "Tianchungosaurus"). The evocative name Technosaurus comes from the Texas Tech University; interestingly, a true basal ornithischian, the European Emausaurus (known only from a skull) also derives its name from a 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 aren’t 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 it was initially believed the only Triassic ornithischian known so far from a complete skeleton (while the remain of the even earlier Pisanosaurus is only partial, and not dinosaurian); today Eocursor is usually considered Early Jurassic like Lesothosaurus, but its completeness gives equally to us precious information about the deepest ornithischian roots, and also could better explain the relationship between bird-hipped dinosaurs and the saurischians. Found even more recently, in year 2014, Kulindadromeus ("Kulinda's runner") from Russia was also a very basal Jurassic ornithischian, with tracks of proto-feathers left.
The Ornithischian Roots
- According to the most accepted classification, ornithischians are divided in two main lineages: Thyreophorans and Neornithischians. The former are Stegosaurs+Ankylosaurs+some basal forms (Scelidosaurus, Scutellosaurus, Emausaurus, and maybe Lesothosaurus). Neornithischians include almost all the other ornithischians. Apart from some basal form, all neornithischians ("new ornithischians") belonged to the group named Cerapods. The latter were furthermore divided in Ornithopods (duckbills, Iguanodon, Camptosaurus etc.) and Marginocephalians (ceratopsians+pachycephalosaurs). Indeed, Cerapods is just a Portmanteau made of “Cera(topsian)” and “(Ornitho)pod”. Recently the belonging of Hypsilophodon in the Ornithopod group has been called into question: Hypsilophodon seems a basal Neornithischian, and not still a proper Cerapod. While the heterodontosaurians probably were even more archaic, having evolved before the split between Thyreophorans and Neornithischians.
First-Known Feathered Ornithischian: Tianyulong
- Tianyulong confuciusi is a heterodontosaurid, believed closer to Fruitadens than to Heterodontosaurus. From the Late Jurassic, it was first found in 2009 in the same Liaoning site from which the Jurassic near-bird Anchiornis was discovered. Another specimen was discovered in 2012. Tianyulong had four tusks like Heterodontosaurus but was slightly smaller (3 ft). Like Anchiornis, it 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.
