Prehistoric Life/Dinosaurs/Primitive Dinosaurs: Difference between revisions

* Thanks to documentaries like [[Walking with Dinosaurs]], several people has become conscious about the existence of ''Coelophysis'', which has become “the forerunner of the dinosaur world”. However, some carnivorous dinosaurs lived ''even before'' it; but are so ancient, that could not even be real theropods. In Triassic world, dinosaurs still were not so differentiated each other, and the familiar “Coelophysis” shape was shared by several other animals, obviously with some degree of variation. ''Herrerasaurus'' and ''Staurikosaurus'' are the two most classic examples. Together, they form their own dinosaur subgroup, Herrerasaurians. Their shape was typically theropodian, but their skeleton was more archaic and less bird-like; for example, they had ''five'' digits in their feet, more similarly to sauropodomorphs than to neotheropods (theropods more derived than herrerasaurs), which have only four. Also their pelvis were unique. This bony-puzzle was responsable of many headaches among paleotaxonomists: ''Herrerasaurus'' and ''Staurikosaurus'' have been variably classified as true theropods, true sauropodomorphs, neither-theropod-nor-sauropodomorph saurischians, or even non-dinosaur dinosauromorphs! ''Herrerasaurus'' was the first discovered, in the 1960s. Found in what is now Argentina, it’s the biggest of the two (4 m [12 ft] long), was longer than a ''Coelophysis'' and much more robust, with a larger, stronger head and much shorter neck. It was arguably a more powerful predator, hunting relatively large animals such as [[Useful Notes/Prehistoric Life Non Dinosaurian Reptiles|rhynchosaurs]], basal synapsids and small-sized dinosaurs, but retreated against the giant prosauropod ''Riojasaurus'' or the 7 m-long Postosuchus-relative ''[[Useful Notes/Prehistoric Life Non Dinosaurian Reptiles|Saurosuchus]]''. Discovered in 1970, ''Staurikosaurus'' shared the same body-structure but was only the size of an ''Ornitholestes'' (2 m [6 ft] long), and arguably hunted smaller preys, perhaps young rhynchosaurs or the primitive ornithischian ''Pisanosaurus''. ''Staurikosaurus'' is one of the most poetically named dinosaurs, “Southern Cross lizard”: it has been for several decades the only dinosaur found in Brazil, and Brazilian flag shows just this constellation. Together, these two dinosaurs have long disputed the title of “the first/most primitive dinosaur ever appeared on Earth”. Among the numerous hypoteses, some paleontologists went to claim herrerasaurians were the ancestors of ''all'' the other dinosaurs: now this hypothesis is totally discarded, since both animals had their specializations on their own.

* Discovered in Argentina in 1993, ''Eoraptor'' (“dawn robber”) suddenly seemed to solve the rivalry between ''Staurikosaurus'' and ''Herrerasaurus'' for the “Whoa, the very first dinosaur ever appeared!” title. When was described, it was thought more primitive than both; however [[Science Marches On|newer studies don't always agree with this]]. 3-4 ft long, the same size of a ''Compsognathus'', ''Eoraptor'' shared with herrerasaurians some skeletal features resembling [[Useful Notes/Prehistoric Life Non Dinosaurian Reptiles|non-dinosaurian archosaurs]]; it too was thought neither saurischian nor ornithischian, but a more basal animal in the middle between true dinosaurs and other dinosauromorphs such as contemporaneous ''[[Useful Notes/Prehistoric Life Non Dinosaurian Reptiles|Lagosuchus]]'' (also found in South America). ''Eoraptor'' has been the most celebrated among all the supposed “first dinosaurs”, in part because was discovered just at the time ''[[Jurassic Park]]'' came to audiences - and the fact scientists gave to it the now-familiar suffix “-raptor” could have done its bit, too. Since then, our “dawn robber” has gained much attention in media, also being object of some degree of sensationalism. Several awesome nicknames were invented, from [[Rule of Cool|the first terror]] to [[Up to Eleven|The father of all killer dinosaurs]]. But [[Real Life]] ''Eoraptor'' wasn't so fearsome, really: it was a tiny, gracile dinosaur, which could even become a meal for a hungry ''Herrerasaurus'' or even a ''Staurikosaurus''. Adding to this, its unspecialized teeth were more probably from an omnivorous rather than carnivorous animal. [[Science Marches On|Science Has Marched On Even More]] as recently as in year 2011, and one study has found ''Eoraptor'' to be a ''very unspecialized sauropodomorph''. Good-bye, “first-terror”.

* Like the basal saurischians above, basal ornithischians as a whole are known only since the 1960s, and still aren’t well-understood. So, every recent discover could be ''very'' significative. ''Eocursor'' and ''Tianyulong'' in particular, are fairly gaining more and more consideration in scientific field because of their objective importance. Found in 2007, ''Eocursor'' (“dawn runner”) was discovered in South Africa like ''Heterodontosaurus'' and ''Lesothosaurus'', and its name is cleary inspired from that of ''Eoraptor'' (“dawn robber”). Its relevance is due to the fact that it’s the ''only'' Triassic ornithischian known so far from a complete skeleton (while the ''Pisanosaurus'' one 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, as is known, Stegosaurs+Ankylosaurs+some basal forms (''Scelidosaurus'', ''Scutellosaurus''). 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”. About ''Tianyulong'' ([[Rhetorical Question Blunder|guess which country it comes from]]?): this is a heterodontosaurid from the Late Jurassic found in 2009 in the same Liaoning site from which the Jurassic troodont ''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'' of course) see [[Useful Notes/Dinosaurs|the useful notes about dinosaurs]] to understand the revolutionary implications of this discovery.