T S A P E H T O T K C BA Our ancestors first stumbled on the remains of dinosaurs in ancient times. The gigantic bones found in Europe were thought to be those of either huge creatures that were described in the Bible as living before the flood or imaginary beings such as dragons or giants.
Dimorphodon
Ichthyosaurus
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Heterodontosaurus
Scientists in the 19th century began to be able to explain the origin of extraordinary fossils, which had been a mystery for thousands of years. After William Buckland, a professor of geology at Oxford University, had studied a large fossilised bone found in limestone at the Stonesfield quarry in England in 1815, he came to the conclusion that it must have belonged to a giant meat-eating lizard. For this reason he called it a Megalosaurus, meaning “great lizard”. This was the first dinosaur about which a proper scientific description was written.
Vulcanodon
The second was the plant-eating Iguanodon. Its tooth inspired the English geologist Gideon Mantell to give it this name, which means “iguana tooth”, in 1825. Sir Richard Owen coined the phrase “dinosaur” in 1841. It means “terrible lizard” from the Greek “deinos” (fearfully great) and “saurus” (lizard). At the same time, he realised that these animals were different from all reptiles, both living and extinct, that were known until then. This meant that they had to be classified in a separate group.
Dilophosaurus
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start (million years) 542 period Cambrian PALAEOZOIC PRECAMBRIAN
490 Ordovician
444 Silurian
416 Devonian
360 Carboniferous
299 Permian
251 200 Triassic Jurassic MESOZOIC
Conquering the land
Ornithosuchus lived some 210 million years ago and was a representative of an advanced group of archosaurs.
The shifting positions of the continents, the changing surface of our planet and the climate change that accompanied this significantly influenced the appearance, evolution, distribution and extinction of the different groups of plants and animals in the course of the history of life on Earth. The first organisms lived in the sea and then, in the Silurian period, when the climate was warm, plants began to appear on land. In the Carboniferous early amphibians came ashore. However, the true conquest of land habitats came later with the evolution of the reptiles in the Permian. These animals had thick impermeable skin, breathed with lungs and reproduced with eggs. Inside each egg there was a membrane to protect the embryo and a yolk to provide nutrients, which meant that the offspring could develop without water. These characteristics allowed the early reptiles to move away from the seas, lakes and rivers, and colonise mountainous regions and drier areas.
REP T ILE RELAT I VES Evolutionary lineages
The evolution of the reptiles divided around 324 million years ago in the Carboniferous period. This division is shown in the structure of the skull, and the reptiles were grouped in two classes according to this. One group is Synapsida, which includes extinct mammal-like reptiles, primitive mammals as well as all mammals living today. The other group is Sauropsida, which is made up of turtles and tortoises, known as anapsids, and diapsids, which include all extinct and living reptiles, birds and their ancestors.
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The first known reptile, Hylonomus, lived about 315 million years ago in the forests of North America. It ate insects and was only 20 cm long.
146 Cretaceous
56 65.5 Palaeocene Eocene CENOZOIC
The Cretaceous was the golden age of dinosaurs with giant creatures such as the 13 m tall Tyrannosaurus…
34 Oligocene
23 Miocene
5.3 0.012 Pliocene Holocene 2.6 Pleistocene
Early dinos Archosauria (archosaurs) is one of the main groups of diapsids. Among their early forms were aquatic and land predators, which had teeth set in sockets in their jaw. Those on land were able to run fast by rising up on their long hind legs without putting their short front legs on the ground, using their tails to balance. Dinosaurs are descended from these bipedal reptiles. The evolutionary line of dinosaurs began to separate from the early archosaurs around 230 million years ago in the Middle Triassic. Flying reptiles, the pterosaurs, and crocodilians (Crocodylia) also evolved from this group. Their forerunners appeared in the Triassic as well.
… as well as the pterosaur Tapejara, which had a 5 m wingspan.
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YS IDEN TIF YING DINO Lizard-hipped and bird-hipped dinosaurs The very first known dinosaurs appeared in north-western Argentina approximately 230–225 million years ago. These early examples looked very similar to each other. They were meat-eating dinosaurs about 1 to 2 metres long. Then plant-eating dinosaurs, which also had a small stature, appeared. By the end of the Triassic, dinosaurs with larger bodies and more complex anatomy had spread from their South American cradle and adapted to a variety of habitats. This continued in the Jurassic and the Cretaceous, creating an extraordinary diversity of species. When compiling the dinosaur family tree, palaeontologists divide the animals into two orders based on the positioning of their pelvic bones (the ilium, ischium and pubis): lizard-hipped or bird-hipped dinosaurs. They are classified into smaller groups according to characteristics of their development, anatomy, diet and other such distinctive features.
SAUROPODOMORPHS These were herbivorous dinosaurs with a small head and a long neck and tail. Early types were bipedal and later sauropodomorphs walked on four legs, some growing to an enormous size. For instance, Seismosaurus was 45 metres long and Supersaurus 42 metres long. Genera: Massospondylus, Bruhatkayosaurus, Diplodocus, Apatosaurus
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The majority of dinos in this group of dinosaurs were carnivores that walked on two legs. Their anatomy and size, however, varied greatly. The bird-like Epidexipteryx was tiny and measured just 25 cm, while at the other extreme the barrel-chested Giganotosaurus with a huge head was 14.5 metres long. Genera: Tyrannosaurus, Rugops, Dromaeosaurus, Velociraptor
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THEROPODS
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Herrerasaurus, a carnivore which lived 230 million years ago, is one of the oldest lizard-hipped dinosaurs.
DINOSAURIA
Saurischians (lizard-hipped dinosaurs)
Ornithischians (bird-hipped dinosaurs)
The pubis of carnivorous lizard-hipped dinosaurs pointed forwards, forming a triangle with the hip bone and the ischium. These provided a good surface for the muscles needed for fast movement to attach to. Gigantic herbivores also belong to this order.
Herbivorous bird-hipped dinosaurs had longer intestines because their digestion was slower, and their backward pointing pubis allowed more space for their digestive system.
Ilium (hip bone) Ischium Pubis
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PACHYCEPHALOSAURS
These fast, bipedal animals were named “thick-headed lizards” because of their high, spongy, domed skull, which in some species such as Pachycephalosaurus was 25 cm thick. Genera: Stegoceras, Pachycephalosaurus, Prenocephale
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Stegosaur
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Ornithopods, whose name means “bird feet”, were plant-eaters with a horny beak. They usually walked on two legs but went down on all fours to graze. This group includes small fast moving creatures as well as larger types with a crest on their head. Genera: Hadrosaurus, Corythosaurus, Parasaurolophus
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ORNITHOPODS
ANKYLOSAURS
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One function of the bony plates along the back of stegosaurs may have been to control body temperature. Huayangosaurus, for example, was an Asian stegosaur living in the Jurassic that was smaller with a taller and shorter skull than the later genera of the Stegosauridae family, which were present in North America. Genera: Lexovisaurus, Stegosaurus
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STEGOSAURS
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Ank
Ankylosaurs were armoured plant-eaters that lived in herds in the Jurassic and Cretaceous. Their back was covered in armour plates and they had a club at the end of their tail to defend themselves against predators. Genera: Saichania, Ankylosaurus, Euoplocephalus
CERATOPSIANS These quadrupeds, known as the “horned” dinosaurs, lived socially, grazing in herds, which protected them to some extent against predators. Later species had frills and horns but the early Psittacosaurus lacked these. Genera: Diabloceratops, Triceratops, Pentaceratops
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CHRO Y NICLE Triassic
G P A N
It seems most likely that dinosaurs first appeared in the territory of modern-day South America in the Triassic period around 230 to 225 million years ago because the earliest known fossil remains have been found there. Early genera such as Eoraptor, Eodromaeus and Staurikosaurus looked similar. These were 1 to 2 metre tall, meat-eating theropod dinosaurs and preyed on plant-eating sauropodomorphs that were small for herbivorous dinosaurs, the 8 metre Plateosaurus This early sauropodomorph, the 3 m tall Mussaurus, lived in South America 215 million years ago. and the 11 metre Riojasaurus. The first representative of bird-hipped dinosaurs (Ornithischia) was the 1 metre tall Pisanosaurus, which already existed 228–220 million years ago. These three main groups of dinosaur spread, perhaps in several waves, across the supercontinent to the territory of modern North AmeriA E ca, Africa, Asia and Europe.
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In the Jurassic Pangaea split into new continents, which resulted in a greater diversity of dinosaurs.
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In the Triassic the ancient continents formed a single supercontinent, which helped the spread of the dinosaurs.
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NORTH AMERICA
EURA
Jurassic During the Jurassic, increasingly advanced types of dinosaur evolved while the primitive species went extinct. By now this group of reptiles ruled the land. Herds of sauropods, which had a small head, long neck and tail and a huge barrel-shaped body, populated the grazing grounds. One such dinosaur was the 6 to 10 metre long Vulcanodon, which was small compared to later species such as the colossal 35 metre long Diplodocus and Brachiosaurus. Among the lizard- hipped meat-eating coelurosaurs, which had a slenderer build, there was a great diversity of species. This group was represented by Coelurus and Ornitholestes in North America and Elaphrosaurus in Africa. Besides these, the early represen tatives of the Carnosauria group, another evolutionary line of theropods, appeared. These species were the top predators of their age, Allosaurus in North America and Yangchuanosaurus in Asia.
In the Cretaceous the separation of the continents created more individual dinosaur communities.
SOUTH AMERICA
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AFRICA AUSTRALIA
Compsognathus, a late Jurassic coelurosaur that lived 150 million years ago, hunted insects and lizards. Its body was probably covered in feather-like structures.
ANTARCTICA
Cretaceous While lizard-hipped dinosaurs typically dominated in the Jurassic, it was the bird-hipped ceratopsians and duck-billed hadrosaurs that reached the peak of diversity in the Cretaceous. Up to the middle of this period known as the golden age of dinosaurs, the giant carnivores were represented by the carcharodontosaurids, while the fish-eating spinosaurids with a semi-aquatic lifestyle were also abundant. Midway through the Cretaceous, these species went extinct, and were replaced as the top predators by tyrannosaurs in
the northern hemisphere and abelisaurs in the southern hemisphere. Of the herbivorous sauropods, the gigantic brachiosaurs and diplodocid dinosaurs vanished, and titanosaurs appeared. The bird-hipped pachycephalosaurs and bird-mimic ornithomimosaurs only lived in the Cretaceous. Life on Earth changed dramatically at the end of the period 65.5 million years ago, when all dinosaurs disappeared probably due to a meteorite strike.
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Hidden in rock Today it is an accepted scientific fact that a couple of hundred million years ago dinosaurs lived on Earth. But how do we know that they really existed? Fossils provide the answer. These are the remains of ancient forms of life and also traces of their lives that have been preserved until today. There are several types of fossil. These include the petrified bones and calcium shells of animals, and impressions of skin, leaves or animal tracks and even dung preserved in stone. Animals with solid structures such as bones or a hard shell are most likely to become fossilised. Soft tissues rot so all that remains of them are impressions.
Thick sedimentary layers are deposited on fossils over millions of years, so often they lie far below the surface.
BONES BROUG H Fossils that tell a story Fossil remains can only be identified and studied after they have been removed from the rock they are embedded in. This job starts in the field, but the meticulous finishing work is done in the laboratory. This preparation requires great accuracy as every detail can contain useful information. Fossils are truly the best guide to the anatomy, stance and even forms of behaviour of dinosaurs. Thanks to palaeontologists studying these petrified remains excavated from the depths of the Earth, skeletons and moving replicas are on display in museums, and realistic visualisations can now bring dinosaurs back to life on film.
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In some cases the movement of the crust of the Earth pushed the fossilised remains close to the surface. Erosion then wore away the stone until the remains were partly revealed and then could be removed by palaeontologists.
Bringing the past to life
Although only the partial skeleton of Balaur has been found, this reveals that, unlike its relative Velociraptor, it did not have one but two oversize retractable claws on its hind legs and had a stockier body.
The first step in reconstructing dinosaurs is to make a skeleton from the available bones. This is not at all easy if the bones are jumbled or incomplete. At such times the remains are compared with similar, known creatures or related animals that are living today in order to complete the skeleton. Fossils of soft tissues are very rare, but when they are found, they help a great deal in determining the shape of the animal. The places where the muscles were attached to the bones can often be identified, which provides a good basis for imagining the muscle system and judging the size of the muscles. An estimate of the volume of the internal organs can be made based on the space between the rib cage and the pelvis. When all these factors are put together, a good idea of the animal’s appearance can be gained.
Assembling the skeleton of Triceratops for exhibition.
HT T O Y LI F E There are several ways of determining the age of fossilised bones or the rock they are in. This enables an estimate of when a particular species of dinosaur such as Ceratosaurus lived. When trying to
decide the colouration and patterns of dinosaurs, scientists look at reptiles, mammals and birds that are alive today and have a similar lifestyle. However, much is left to the imagination of the artist.
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