Prehistoric Life/Dinosaurs/Primitive Dinosaurs: Difference between revisions

{{tropeUseful Notes}}

* Giving the coup-de-grace to ''Eoraptor'', its common-ancestor-of-all-dinosaurs title is now contended by other dinosaurs found in the 2000s. Astonishingly, they all come from South America, which could be renamed “the cradle of the dinosaur kind” at this point. The most enigmatic ones make together the Guaibasaurids. These saurischians were extremely generic and unspecialized dinosaurs, whose external shape was ''really'' in the middle between a small theropod and a "prosauropod", not deceptively theropodian like herrerasaurians or ''Eoraptor''. The namesake ''Guaibasaurus'' was the first discovered and initially considered a possible basal theropod; then, the mythical-named ''Saturnalia'' <ref> “Saturnalia” is a plural Latin name for a kind of feast made by Ancient Romans to celebrate Saturn, the goddity who protected their crops.</ref> from Brazil, which was initially believed the “first prosauropod'”. In the second half of the 2000s, scientists decided that both dinosaurs were too basal to be either theropods or sauropods, and put together in the same family, Guaibasaurids. Now they are often considered very basal sauropodomorphs, though this, too, [[Science Marches On|may still change]]. With their unspecialized traits, guaibasaurids were almost surely omnivorous creatures; indeed, a third member found in 2009 has received a meaningful name: ''Panphagia'', “[[Extreme Omnivore|eat-all]]”.

* Among basal Ornithischian dinosaurs, there were curious things as well. ''Heterodontosaurus'', for example, might be renamed the [[Full Boar Action|boar]]-[[Feathered Friends|bird]]. Living in Early Jurassic South Africa 190 million years ago, ''Heterodontosaurus'' superficially resembled the ornithopod ''Hypsilophodon'' with its slender, bipedal body, but was even smaller (1.20 m/4 ft long), more robust and with longer forelimbs. Discovered only in the sixties, its name means “lizard with different teeth”, and with reason: no other dinosaur had such a diversified dentition, with ''three'' kinds of teeth surprisingly similar to those found in mammals. The most noticeable are two pairs of canine-like “tusks” visible when the mouth closed, giving it a vaguely boar-like look; behind, molar-like teeth to grind up tough vegetation; in front of them, small peg-like teeth only on the tip of its upper jaw. With this dentition, ''Heterodontosaurus'' was probably a mostly herbivorous omnivore, eating insects other than vegetation, while the tusks could have been used for display and/or competiton. Some scientists suspect only males did have the large canines, but there is no evidence. Other close relatives, like ''Abrictosaurus'', are devoid of tusks: their skull could either pertain to females, or, more probably, to totally tusk-less species. All these animals make together their own ornithischian family, Heterodontosaurids. Once thought ornithopods or ancient relatives of ceratopsians and pachycephalosaurs, now they are regarded as very basal ornithischians. Despite their primitiveness, heterodontosaurs not only flourished in the Early Jurassic, but also managed to survive until the Early Cretaceous, with species such as the poorly-known ''Echinodon''.

* When talking about Ornithischians, we can find the same issues of Saurischians: in the Triassic/Early Jurassic they were all so-similar each other, it’s hard task to classify them accurately. Nonetheless, they are extremely important animals for scientists, no matter their often tiny size. Other than ''Heterodontosaurus'', we have several other examples. ''Lesothosaurus'', ''Scutellosaurus'' and ''Pisanosaurus'' have traditionally been the most relevant. ''Lesothosaurus'' in particular was once considered the forerunner of all bird-hipped dinos, and thought not to belong to any great ornithischian group; [[Science Marches On|recent research]] suggest it could be a very basal Thyreophoran, thus ancestor of Stegosaurs and Ankylosaurs. Also from Early Jurassic Southern Africa, its name derives from [[Exactly What It Says on the Tin|the Kingdom of Lesotho]] (a small South African enclave) where its remains were dug out in 1978. Merely 3 ft long, the bulk of a ''Compsognathus'', ''Lesothosaurus'' seems not to have any specialization in its anatomy. Its mouth had simple teeth and small cheeks, its forelimbs short and five-digited, its hindlimbs apt for running. It was said that ''Lesothosaurus'' resembles a lizard more than any other dinosaur. Fragmentary remains that have been named "Fabrosaurus" may be synonymous with this taxon; since they were named before ''Lesothosaurus'', in old textbooks this dinosaur is often referred “Fabrosaurus”. ''Scutellosaurus'': has traditionally been the most primitive thyreophoran. Discovered only in the 1980s, was also a small bipedal animal with a similar look, but slighty bigger, longer-tailed, more robustly-built than the lesothosaur, and with a light armor made by small bony plates placed in rows upon its torso, similar to that of the bigger ''Scelidosaurus''. Like the scelidosaur, ''Scutellosaurus'' lived in Early Jurassic, but was found in Arizona, where the popular double-crested ''[[Stock Dinosaurs|Dilophosaurus]]'' lived (and could have been its predator). Also found in the last decades of the XX century, the Argentinian ''Pisanosaurus'' lived with the alleged “first theropods ''Eoraptor'' and ''Herrerasaurus'', and still remains the most ancient ornithischian known to science. Sadly, is known only from one incomplete fossil, but was arguably similar to ''Lesothosaurus'' in shape and size. One curious thing is that some Triassic non-dinosaurian archosaurs were once considered basal ornithischians as well: "Technosaurus" from Texas is one example.

[[Category:Prehistoric Life Primitive Dinosaurs]]