PHRS Dinosaur

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dinosaur

Greek deinos 'terrible', sauros 'lizard'

Any of a group (sometimes considered as two separate orders) of

extinct reptiles living between 205 million and 65 million years ago.Their closest living relations are crocodiles and birds. Many speciesof dinosaur evolved during the millions of years they were thedominant large land animals. Most were large (up to 27 m/90 ft),but some were as small as chickens. They disappeared 65 millionyears ago for reasons not fully understood, although many theoriesexist, perhaps the most widely accepted being that the Earth wasstruck by a comet.

Classification

Dinosaurs are divisible into two unrelated stocks, the ordersSaurischia ('lizard-hip') and Ornithischia ('bird-hip'). Members ofthe former group possess a reptile-like pelvis and are mostly bipedaland carnivorous, although some are giant amphibious quadrupedalherbivores. Members of the latter group have a bird-like pelvis, aremainly four-legged, and entirely herbivorous.

The Saurischia are divided into: theropods ('beast-feet'), includingall the bipedal carnivorous forms with long hindlimbs and short

forelimbs (tyrannosaurus, megalosaurus); and sauropodomorphs('lizard-feet forms'), including sauropods, the large quadrupedalherbivorous and amphibious types with massive limbs, long tailsand necks, and tiny skulls (diplodocus, brontosaurus).

The Ornithischia were almost all plant-eaters, and eventuallyoutnumbered the Saurischia. They are divided into four suborders:ornithopods ('bird-feet'), Jurassic and Cretaceous bipedal forms(iguanodon) and Cretaceous hadrosaurs with duckbills; stegosaurs('plated' dinosaurs), Jurassic quadrupedal dinosaurs with a double

row of triangular plates along the back and spikes on the tail(stegosaurus); ankylosaurs ('armoured' dinosaurs), Cretaceousquadrupedal forms, heavily armoured with bony plates(nodosaurus); and ceratopsians ('horned' dinosaurs), UpperCretaceous quadrupedal horned dinosaurs with very large skullsbearing a neck frill and large horns (triceratops).

These two main dinosaur orders form part of the superorderArchosaurus ('ruling reptiles'), comprising a total of five orders. Theother three are Pterosaurs ('winged lizards'), including pterodactyls,

of which no examples exist today, crocodilians, and birds. All fiveorders are thought to have evolved from a 'stem-order', theThecondontia.

dinosaurexcavation

Bird: Fossils ofEarly Birds

Dinosaur:Cloning fromPreserved DNA

Dinosaur: TheBiggest and theOldest

Extinction: ARace againstTime

What Killed theDinosaurs?

DinosaurExtinctionHypothesis

Dinosauria

Dinosaur TraceFossils

Early DinosaurDiscoveries inNorth America

World's FirstDinosaurSkeleton:HadrosaurusFoulkii

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SpeciesBrachiosaurus, a long-necked plant-eater of the sauropod group,was about 12.6 m/40 ft to the top of its head, and weighed 80tonnes. Compsognathus, a meat-eater, was only the size of achicken, and ran on its hind legs. Stegosaurus, an armoured plant-

eater 6 m/20 ft long, had a brain only about 3 cm/1.25 in long. Notall dinosaurs had small brains. At the other extreme, the huntingdinosaur stenonychosaurus, 2 m/6 ft long, had a brain sizecomparable to that of a mammal or bird of today, stereoscopicvision, and grasping hands. Many dinosaurs appear to have beenequipped for a high level of activity. Tyrannosaurus was a huge,two-footed, meat-eating theropod dinosaur of the Upper Cretaceousin North America and Asia. The largest carnivorous dinosaur wasGiganotosaurus carolinii. It lived in Patagonia about 97 millionyears ago, was 12.5 m/41 ft long, and weighed 68 tonnes. Its

skeleton was discovered in 1995.

Theories of extinctionA popular theory of dinosaur extinction suggests that the Earth wasstruck by a giant meteorite or a swarm of comets 65 million yearsago and this sent up such a cloud of debris and dust that climateswere changed and the dinosaurs could not adapt quickly enough.The evidence for this includes a bed of rock rich in iridium anelement rare on Earth but common in extraterrestrial bodies datingfrom the time.

An alternative theory suggests that changes in geography broughtabout by the movements of continents and variations in sea level ledto climate changes and the mixing of populations betweenpreviously isolated regions. This resulted in increased competitionand the spread of disease.

Archaeological findingsThe term 'dinosaur' was coined in 1842 by the English

palaeontologist Richard Owen, although there were findings ofdinosaur bones as far back as the 17th century. In 1822 G A Mantell(17901852) found teeth of iguanodon in a quarry in Sussex. Thefirst dinosaur to be described in a scientific journal was in 1824,when William Buckland, professor of geology at Oxford University,published his finding of a 'megalosaurus or great fossil lizard' foundat Stonesfield, a village northwest of Oxford, England, although amegalosaurus bone had been found in 1677.

One of the largest dinosaur species found in the UK was a sauropod,

Cetiosaurus oxoniensis, discovered in 1870 near Bletchingdon,north of Oxford. It was around 15 m/49 ft long, although specimenshave been discovered in North Africa up to 18 m/60 ft long. In 1992

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another large dinosaur,Iguanodon bernissartensis, was discoverednear Ockley in Surrey, England, by amateur fossil hunters.

An almost complete fossil of a dinosaur skeleton was found in 1969in the Andean foothills, South America; it had been a two-leggedcarnivore 2 m/6 ft tall and weighed more than 100 kg/220 lb. Morethan 230 million years old, it is the oldest known dinosaur. In 1982a number of nests and eggs were found in 'colonies' in Montana,suggesting that some bred together like modern seabirds. In 1987finds were made in China that may add much to the traditionalknowledge of dinosaurs, chiefly gleaned from North Americanspecimens. In 1989 and 1990 an articulated Tyrannosaurus rex wasunearthed by a palaeontological team in Montana, with a full skull,one of only six known. Short stretches of dinosaur DNA wereextracted in 1994 from unfossilized bone retrieved from coal

deposits approximately 80 million years old.

Recent discoveriesThe discovery of a small dinosaur was announced in China in 1996.Sinosauropteryx lived about 120 million years ago and was 0.5m/1.6 ft tall. It had short forelegs, a long tail, and short feathers,mainly on its neck and shoulders.

In 1997 US scientists claimed that 65 million-year-old remainsdiscovered in the Atlantic Ocean were proof that a massive asteroid

impact on Earth killed the dinosaurs. A sea-drilling expeditiondiscovered three samples that have the signature of an asteroidimpact. Previous evidence from sediment suggested that thedinosaurs did not become extinct at exactly the same time as animpact occurred. The new evidence appeared to substantiate thetheories of geologists such as Walter Alvarez, who championed thetheory that the dinosaurs disappeared from fossil history because ofsuch an impact.

US palaeontologists discovered in 1997 a dinosaur wishbone inplace in the skeleton of a velociraptor. This was the first time awishbone had been found in place and scientists claimed that thisconstitutes strong evidence for birds having evolved from dinosaurs.

The fossil of a previously unknown dinosaur was discovered inNiger in 1998. The crocodile-like fish-eater has been namedSuchomimus and lived 100 million years ago. It was about 11m/36ft in length (with a 1-m/3-ft jaw) and weighed about 4 tonnes.

A new species of carnivorous dinosaur was discovered in Argentinain 2000. Several skeletons were found at the same site, so thespecies is thought to have been social, and about 1 m/3.3 ft longer

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