Title: Dinosaur Content: Dinosaurs are a varied group of Archosaur reptiles.The word 'dinosaur' comes from Greek, meaning 'terrible lizard, [] and was coined by English biologist Richard Owen in 1842. [] Dinosaurs are related to birds and crocodiles. They were the most powerful land animals of the Mesozoic era. Over 500 different genera of dinosaurs are known.That is, fossil dinosaurs and not modern birds. Fossils of dinosaurs have been found on every continent, and there are still new discoveries. Dinosaurs began in the Upper Triassic, about 230 million years ago.They may have began earlier: The earliest date of a dinosaur fossil is that of Eoraptor and Herrerasaurus from Argentina, and Saturnalia from Brazil, 237 to 228 mya.Benton M.J. 2015. Vertebrate palaeontology. 4th ed, Wiley Blackwell, p205. By the early Jurassic they were the top land vertebrates, and dominated most environments on land. They continued until the K/T extinction event 66 million years ago. From the fossil record, it is known that birds are living feathered dinosaurs. They evolved from earlier theropods during the later Jurassic. They were the only line of dinosaurs to survive to the present day. Dinosaurs had adaptations that helped make them successful. The first known dinosaurs were small predators that walked on two legs.Moderately large bipedal dinosauromorphs had appeared by 246 mya. Fossil tracks show that the dinosaur lineage appeared soon after the Permian-Triassic extinction event. Their age suggests that the rise of dinosaurs was slow and drawn out across much of the Triassic. All their descendants had an upright posture, with the legs underneath the body. This transformed their whole life- style. There were other features. Most of the smaller dinosaurs had feathers, and were probably warm-blooded. This would make them active, with a higher metabolism than modern reptiles. Social interaction, with living in herds and co-operation, seems certain for some types. The existence of communal egg- laying sites is best understood if the adults travelled in herds, as herbivores do today. The first fossils were recognised as dinosaurs in the early 19th century. Some of their bones were found much earlier, but were not understood. William Buckland, Gideon Mantell and Richard Owen saw these bones were a special group of animals. Dinosaurs are now major attractions at museums around the world. They have become part of popular culture. There have been many best-selling books and movies. New discoveries are reported in the media. thumb|center|500px|Evolution of dinosaurs == Dinosaur features == Dinosaurs are so varied that it is not easy to find what they all share. A reasonable list would include many features of the skeleton which are not familiar to the general reader.Nesbitt, Sterling J. 2011. The early evolution of Archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History. New York: American Museum of Natural History. 2011 (352): 1–292. doi:10.1206/352.1. hdl:2246/6112. ISSN 0003-0090. S2CID 83493714. Dinosaurs were, at the start, small and bipedal: they walked on their hind legs. They laid eggs in nests, and included both carnivores and herbivores.We now know that birds are their living descendents, and more about that later. Changes in the basic set-up of dinosaurs happened because of adaptations to different lifestyles. From the start of their fossil record, there were both herbivores and carnivores. ==Types of dinosaurs== Dinosaurs are united by at least 21 traits in their skulls and skeletons.Nesbitt S.J. 2011. The early evolution of archosaurs : relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 1–292. These common characters (called 'synapomorphies') are the reason palaeontologists are sure dinosaurs had a common origin. However, when definite dinosaur fossils appear (early in the Upper Triassic), the group had already split into two great orders, the Saurischia, and the Ornithischia. The Saurischia keep the ancestral hip arrangement inherited from their Archosaur ancestors, and the Ornithischia have a modified hip structure. center|500px A. Eoraptor, an early saurischian, B Lesothosaurus, a primitive ornithischian, C A saurischian pelvis (Staurikosaurus) D Lesothosaurus pelvis ===Dinosaur classification=== The following is a simplified list of dinosaur groups based on their evolution. Groups with a dagger (†) next to them don't have any living members. *Dinosauria :*Saurischia ("lizard-hipped"; includes Theropoda and Sauropodomorpha) ::*Theropoda (all bipedal; most were carnivorous) :::*†Herrerasauria (early bipedal carnivores) :::*†Coelophysoidea (small, early theropods; includes Coelophysis and its close relatives) :::*†Dilophosauridae (early crested and carnivorous theropods) :::*†Ceratosauria (generally elaborately horned, the dominant southern carnivores of the Cretaceous) :::*Tetanurae (meaning "stiff tails"; includes most theropods) ::::*†Megalosauroidea (early group of large carnivores including the semiaquatic spinosaurids) ::::*†Carnosauria (Allosaurus and close relatives, like Carcharodontosaurus) ::::*Coelurosauria (feathered theropods, with a range of body sizes and niches) :::::*†Compsognathidae (common early coelurosaurs) :::::*†Tyrannosauridae (Tyrannosaurus and its close relatives) :::::*†Ornithomimosauria (meaning "ostrich-mimics"; mostly toothless; carnivores to possible herbivores) :::::*†Alvarezsauroidea (small insectivores with short arms that each had one large claw) :::::*Maniraptora (meaning "hand snatchers"; had long, slender arms and fingers) ::::::*†Therizinosauria (bipedal herbivores with large hand claws and small heads) ::::::*†Oviraptorosauria (mostly toothless; their diet and lifestyle are uncertain) ::::::*†Archaeopterygidae (small, winged theropods or primitive birds) ::::::*†Deinonychosauria (small to medium-sized, bird-like, with a distinctive toe claw.) ::::::*Avialae (modern birds and their extinct relatives) :::::::*†Scansoriopterygidae (small primitive avialans with long third fingers) :::::::*†Omnivoropterygidae (large, early short-tailed avialans) :::::::*†Confuciusornithidae (small toothless avialans) :::::::*†Enantiornithes (primitive flying avialans that lived in trees) :::::::*Euornithes (advanced flying birds) ::::::::*†Yanornithiformes (toothed Cretaceous Chinese birds) ::::::::*†Hesperornithes (specialized aquatic diving birds) ::::::::*Aves (modern, beaked birds and their extinct relatives) ::*†Sauropodomorpha (herbivores with small heads, long necks, long tails) :::*†Guaibasauridae (small, primitive, omnivorous sauropodomorphs) :::*†Plateosauridae (primitive, bipedal "prosauropods") :::*†Riojasauridae (small, primitive sauropodomorphs) :::*†Massospondylidae (small, primitive sauropodomorphs) :::*†Sauropoda (very large and heavy, usually over long; quadrupedal) ::::*†Vulcanodontidae (primitive sauropods with pillar-like arms and legs) ::::*†Eusauropoda ("true sauropods") :::::*†Cetiosauridae ("whale reptiles") :::::*†Turiasauria (European group of Jurassic and Cretaceous sauropods) :::::*†Neosauropoda ("new sauropods") ::::::*†Diplodocoidea (skulls and tails elongated; teeth typically narrow and pencil-like) ::::::*†Macronaria (boxy skulls; spoon- or pencil-shaped teeth) :::::::*†Brachiosauridae (long-necked, long-armed macronarians) :::::::*†Titanosauria (diverse; stocky, with wide hips; most common in the late Cretaceous of southern continents) :*†Ornithischia ("bird-hipped"; diverse bipedal and quadrupedal herbivores) ::*†Heterodontosauridae (small basal ornithopod herbivores/omnivores with prominent canine-like teeth) ::*†Thyreophora (armored dinosaurs; mostly quadrupeds) :::*†Ankylosauria (scutes as primary armor; some had club-like tails) :::*†Stegosauria (spikes and plates as primary armor) ::*†Neornithischia ("new ornithischians") :::*†Ornithopoda (various sizes; bipeds and quadrupeds; evolved a method of chewing using flexible skulls and many teeth) :::*†Marginocephalia (Had dome- like growths on their skulls made of bone) ::::*†Pachycephalosauria (bipedal with domed or knobby growth on skulls) ::::*†Ceratopsia (quadrupeds with frills; many also had horns) :::# ==Dinosaur origins and evolution== ===Archosaurs=== The Archosaurs evolved into two main clades: those related to crocodiles, and those related to dinosaurs. * Archosauria **Pseudosuchia: clade of the crocodiles and their relatives. ** Avemetatarsalia: clade of the dinosaurs, pterosaurs, birds and relatives. ***Aphanosauria ***Ornithodira: clade of the pterosaurs and dinosaurs. ****Pterosaurs **** Dinosaurs ===Earliest dinosaurs=== The first known dinosaurs were bipedal predators that were one to two metres long.Palaeos lists "probably habitually bipedal" among the characteristics of the Dinosauromorpha (that is, early proto-dinosaurs). Allen, Vivian; Bates, Karl T; Li, Zhiheng and Hutchinson John R. 2013. Linking the evolution of body shape and locomotor biomechanics in bird-line archosaurs. Nature 497, 104–107. ; popular summary The earliest confirmed dinosaur fossils include the saurischian ('lizard-hipped') dinosaurs Herrerasaurus 230–220 mya, Staurikosaurus possibly 230–225 mya, Eoraptor 231.4 mya,Alcober O.A & Martinez R.N. 2010. A new herrerasaurid (Dinosauria, Saurischia) from the Upper Triassic Ischigualasto Formation of northwestern Argentina. Zookeys. 63, 5581. and Alwalkeria 230–220 mya. Saturnalia, 232–225 mya, may be a basal saurischian or a prosauropod. The others are basal saurischians. Among the earliest ornithischian ('bird-hipped') dinosaurs is Pisanosaurus 230–220 mya. Although Lesothosaurus comes from 199–189 mya, skeletal features suggest that it branched from the main Ornithischia line at least as early as Pisanosaurus. Early saurischians were similar to early ornithischians, but different from modern crocodiles. Saurischians differ from ornithischians by keeping the ancestral configuration of bones in the pelvis (shown in a diagram above). Another difference is in the skull: the upper skull of the Ornithischia is more solid, and the joint connecting the lower jaw is more flexible. These features are adaptations to herbivory; in other words, it helped them grind vegetable food. ==Adaptive radiation== Dinosaurs were a varied group of animals. Adaptive radiation happened. This let them live in many ecological niches. Paleontologists have identified over 500 different genera and 1,000 species of non-avian dinosaurs. Their descendants, the birds, number 9,000 living species, and are the most diverse group of land vertebrates. The largest dinosaurs were herbivores (plant-eaters), such as Apatosaurus and Brachiosaurus. They were the largest animals to ever walk on dry land. Other plant-eaters, such as Iguanodon, had special weapons to help them fight off the meat-eaters. For example, Triceratops had three horns on its head shield, Ankylosaurus was covered in boney plates, and Stegosaurus had spikes on its tail. The carnivores were bipedal (walked on their back legs), though not as we do. Their body was more towards the horizontal, balanced at the back by their tail. Some were very large, like Tyrannosaurus, Allosaurus and Spinosaurus, but some were small, like Compsognathus. It was the smaller sized meat-eaters that may have evolved into birds. The first fossil bird, Archaeopteryx, had a skeleton which looked much like that of the dinosaur Compsognathus, as T.H. Huxley commented. ==Life style== ===Locomotion=== Dinosaurs were primitively bipedal: their probable ancestors were small bipedal Archosaurs. The date of the early dinosaur genus Eoraptor at 231.4 million years ago is important. Eoraptor probably resembles the common ancestor of all dinosaurs; its traits suggest that the first dinosaurs were small, bipedal predators. The discovery of primitive, pre-dinosaur,A clade of Archosaurs ancestral to all dinosaurs and pterosaurs. types in Middle Triassic strata supports this view. Analysis of their fossils suggests that the animals were indeed small, bipedal predators. thumb|right | 300px | Hip joints and hindlimb postures Those dinosaurs which returned to four-legged stance kept all four legs under their body. This is much more efficient than the sprawling legs of a lizard. The big sauropods could never have reached so large a size without their pillar-like legs. A review surveys what we know about the mechanics of dinosaur movement.Alexander, R. McNeil 2006. Dinosaur biomechanics. Proceedings of the Royal Society B: Biological Sciences. 273 (1596): 1849–1855. (full free access) ===Warm blooded=== A major change in outlook came in the 1960s, when it was realised that small theropods were probably warm-blooded.Bakker, Robert T. 1986. The dinosaur heresies: new theories unlocking the mystery of the dinosaurs and their extinction. Citadel N.Y. The question of whether all theropods or even all dinosaurs were warm blooded is still undecided. It is now certain (from fossils discovered in China: see Jehol biota) that small theropods had feathers. This fits well with the idea that they were warm-blooded, and that the origin of birds can be traced to a line of small theropods. ===Activity=== Warm blooded animals have a high metabolic rate (use up food faster). They can be more active, and for longer, than animals who depend on the environment for heating. Therefore, the idea of warm-blooded dinosaurs insulated by feathers led to the idea that they were more active, intelligent and faster runners than previously thought. Main-stream palaeontologists have followed this view for small theropods, but not for larger herbivores.Benton M.J 2000. Walking with dinosaurs: the facts. BBC, London, Chapter 6. Since we know that the size of a Stegosaur's brain was about the size of a walnut, there is good reason to think its intelligence was limited. ===Limitations=== Despite their great success over a long period, there were life-styles which the dinosaurs never evolved. None ever evolved to live entirely in water, as many mammals do, though Spinosaurus was semi- aquatic. They never dominated the small terrestrial niche. All through the Mesozoic most small vertebrates were mammals and lizards. ==Extinction== The extinctions at the end of the Cretaceous were caused by one or more catastrophic events, such as massive asteroid or meteorite impacts (like the Chicxulub impact), or increased volcanic activity. Several impact craters and massive volcanic activity, such as that in the Deccan Traps in India, have been dated to the approximate time of the extinction event. These geological events may have reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology. Did any terrestrial dinosaurs survive the great extinction event? Several fossils have been found in the Hell Creek Formation about 40,000 years later than the K/T extinction event. Many scientists dismiss the "Paleocene dinosaurs" as re-worked, that is, washed out of their original places and then re-buried in much later sediments. An associated skeleton (e.g. more than one bone from the same individual) found above the K/T boundary would be convincing, but no such finds have been reported. ==Dinosaurs in fiction== :"...Dragons of the prime, that tare each other in their slime". Tennyson, In Memoriam,1849. Books about dinosaurs have been popular, especially with children, but adults have also enjoyed these kinds of books. In Edwardian times, Arthur Conan Doyle wrote a novel about a plateau filled with dinosaurs which he called The Lost World. Jurassic Park in 1990 started a new phase in dinosaur popular culture. ===Novel and film adaptations=== *Jurassic Park (novel), a 1990 novel by Michael Crichton **Jurassic Park (film), the 1993 film adaptation directed by Steven Spielberg, based on the novel **The Lost World: Jurassic Park (1997), the second film in the series **Jurassic Park III (2001), the third film in the series ==Related pages== *List of dinosaurs *Dinosaur brains and intelligence *For "dinobirds", see Origin of birds *K/T extinction event