3. The Cretaceous Period

The Cretaceous Period

144 to 65 Million Years Ago

The Cretaceous is usually noted for being the last portion of the "Age of Dinosaurs", but that does not mean that new kinds of dinosaurs did not appear then. It is during the Cretaceous that the first ceratopsian and pachycepalosaurid dinosaurs appeared. Also during this time, we find the first fossils of many insect groups, modern mammal and bird groups, and the first flowering plants.

Ceratopsian

Pachycephalosaurus

The breakup of the world-continent Pangaea, which began to disperse during the Jurassic continued. This led to increased regional differences in floras and faunas between the northern and southern continents.

The end of the Cretaceous brought the end of many previously successful and diverse groups of organisms, such as non-avian dinosaurs and ammonites. This laid open the stage for those groups which had previously taken secondary roles to come to the forefront. The Cretaceous was thus the time in which life as it now exists on Earth came together.

The age of dinosaurs reached its apex during the Cretaceous period, which occurred 145 to 65 million years ago. Dinosaur and other animal diversity characterized this time, as more different types of dinosaurs emerged during the Cretaceous than in any other period. Nevertheless, ominous signs began to surface, hinting at the non-avian dinosaur downfall that would mark the end of this final phase of the Mesozoic era.

Cretaceous Geology, Climate and Plant Life

Laurasia, a portion of the former Pangea supercontinent, consisted of the present-day continents of North America, Europe and much of Asia. Another section of former Pangea was referred to as Gondwana, which included Africa, Antarctica, Arabia, Australia, India and South America. Both Laurasia and Gondwana broke into pieces during the Cretaceous, leading to the separate continents. North America, however, was substantially different than it is today. A shallow sea split it in half, turning the western portion into an island.

Although wet and dry periods existed before this time, the seasons became more distinct during the Cretaceous. Flowering plants emerged, providing another food source for dinosaurs. The first flowers were mostly like small weeds but, like weeds today, they grew and spread well, quickly moving from tropical to cooler regions. Oak, maple, walnut and other trees also emerged.

The Largest Flying Animals

Pteranodon

Cretaceous skies were full of creatures big and small. Minuscule moths and small bees shared airspace with enormous pterosaurs, which were warm-blooded flying reptiles related to dinosaurs. The pterosaur Pteranodon, which had a wingspan of up to 33 feet, was one of the biggest of the bunch. It spent much of its time soaring over water, looking for fish, crabs, insects and mollusks to eat.

Dinosaur Diversity

Big, small, spiked, fat and more, dinosaurs of all shapes and sizes appeared during the Cretaceous. Since the landmasses were now separated, animals on the distinct continents went their separate evolutionary ways. Beaked, plant-eating dinosaurs known as ceratopsians first appeared at this time. One of the most well-known members of this group was Triceratops, which had three facial horns and a large, bony frill. The so-called "bone-headed" dinosaurs also emerged during the Cretaceous. One of the biggest was Pachycephalosaurus, which had front teeth and might have even enjoyed meat with its plant-based diet.

Ceratopsian

Triceratops

Pachycephalosaurus

Numerous carnivorous dinosaurs preyed upon the other dino bounty. There was Pelicanimimus, which had more teeth — around 220 — than any other known dinosaur. Afrovenator used its own bladelike teeth to tear at the flesh of prey. Carnotaurus had such short arms that its hands appeared to form out of its elbows, but its clawed feet and sharp teeth could still take down sauropods. Tyrannosaurus rex, however, stood out from the carnivorous dinosaur pack. This 40-foot-long beast was so strong that researchers believe it could shake victims to death, once it had sunk its teeth into their bodies.

Pelicanimimus

Afrovenator

Carnotaurus

T-Rex

The Cretaceous period marks the end of the age of Dinosaurs with what is known as the Great Extinction. However, this period gives us some of the most beloved dinosaurs of modern days, like the Triceratops and, of course, the Tyrannosaurus-rex, king of the dinosaurs.

Hints of Extinction

Not all dinosaurs thrived during the Cretaceous. Stegosaurs, which lacked the protective armor of other plant eaters, like ankylosaurs, went into a population decline. In northern areas, long-necked sauropods began to disappear. While minor, these changes might have foreshadowed the mass extinction that marked the end of both the Cretaceous period and the dinosaur age.

Ankylosaurs

Sauropods

The Great Extinction

 

While the cause of the massive extinction brought on at the end of the Cretaceous period is debated, many theories exist. There is evidence of plant decay which would have contributed to the extinction, as all dinosaurs, whether directly or indirectly, depended on plant life. This could have been caused by large asteroid collisions or volcanic eruptions or both. These events would have suspended sunlight, causing plant life to diminish. Other theories include the regression of the sea level, or a combination of many of these possibilities. Most of the species that survived were not as dependent on plant life. Insects survived on other animals and dead organisms and mammals would often feed on insects. This allowed the Mammals to survive until the present day when mammals would replace the dinosaurs as the dominant species.

2. Dinosaurs of the Jurassic Period

Jurassic Period

A period of the Mesozoic era, spanning the time between the Triassic and the Cretaceous periods, about 206 to 144 million years ago. The start of the period is marked by the major Triassic-Jurassic mass extinction. Named for the Jura Mountains on the border between France and Switzerland, where rocks of this age were first studied, the Jurassic became a household word with the success of the movie Jurassic Park – although most of the dinosaurs featured in the film actually lived during the Cretaceous.

reptiles dominated the land, sea, and air. During this period, vegetation was greener and more lush. By the late Jurassic, great dinosaurs such as Brachiosaurus, Allosaurus, Ceratosaurus, and Stegosaurus, had evolved on land. Pterosaurs ruled the skies and the earliest known birds appeared.

The Jurassic was the beginning of the age when reptiles dominated the land, sea, and air. During this period, vegetation was greener and more lush. By the late Jurassic, great dinosaurs such as Brachiosaurus, Allosaurus, Ceratosaurus, and Stegosaurus, had evolved on land. Pterosaurs ruled the skies and the earliest known birds appeared.

The Jurassic Period also saw the breakup of the super-continent Pangea, which began in the Triassic, continue. At the start of the early Jurassic period, the giant continent Pangaea broke up, forming the beginning of the world that we now know. There were huge volcanoes with rivers of lava and clouds of poison gases.

Land that had been part of the interior of the huge continent was now coastline of smaller continents, and the climate began to change accordingly.

Forests of ferns, ginkgo trees, cycads and conifers grew. All these plants can still be seen today. Scuttling about at the bottom of these plants were the early mammals, all of them rat-sized.

Sauropods were gigantic herbivores

The dominant land animals were the huge dinosaurs, the largest land animals ever. They were the gigantic herbivore (plant-eaters) sauropods such as Diplodocus and Brachiosaurus. Other herbivores included Stegosaursaurus. Carnivorous (meat-eating) dinosaurs included Allosaurus and Dilophosaurus.

Allosaurus

Dilophosaurus

Dilophosaurus

The dinosaurs of the Jurassic were much more different from each other than in other periods: there was a greater variety. Because of the different climate, the forests grew, and the herbivores became huge in order to feed on the tall trees. The carnivores then had to become larger and more fierce to deal with such huge prey.

The first birds appeared, such as Archaeopteryx. The seas were full of marine reptiles such as the plesiosaurs, crocodiles, ichthyosaurs, sharks and rays.

The first birds the Archaeopteryx appeared in the Jurassic Period

Plesiosaurs

Ichthyosaurs

Some Dinosaurs of the Jurassic Period

1.Stegosaurus  (say steg-uh-SAW-rus)

Stegosaurus lived about 160-145 million years ago during the late Jurassic Period. It was over 8 metres long and weighed about 2 1/2 tonnes. Stegosaurus had a big tail with metre-long spikes at the end for protection against predators.The back legs were twice as long as the front legs. It had a tiny head containing a tiny brain. Its mouth was a toothless beak. It had large, flat, triangular plates along its back, rather like armour. Palaeontologists believe that the triangular plates along the back and tail helped it keep its temperature under control. They may also have been used to attract other stegosaurs. They were made of bone that was not solid, but which had tunnels like tubes along them.
The first Stegosaurus fossil was discovered in Colorado, USA in 1877.

2.Allosaurus (say all-oh-SAW-rus)

The name means 'different lizard', because its vertebrae (bones of the spine) are different from that of other dinosaurs. Allosaurus lived about 150 to 145 million years ago in the Late Jurassic period. It was about 12m long and weighed up to 3 tonnes

Allosaurus was a 'lizard-hipped' dinosaur (or theropod). It had a bony crest above each eye and an s-shaped neck. It moved on its two strong back legs.

The back legs had three toes pointing forward and one pointing backwards. It was not a fast runner however. It had a powerful tail.

Allosaurus was a carnivore with big, curved teeth that were grooved for extra sharpness. The strength in its back and neck helped its jaws tear up its prey. Allosaurus had short arms with three long claws that held onto prey such as large sauropods. Allosaurus had quite short arms compared to its legs, but they were powerful. They had three long, hook-like claws that were important for attacking and holding on to prey.

More than 60 Allosaurus skeletons have been found in Wyoming, New Mexico and Utah in the USA, and Tanzania . The most complete was found in 1883.

3.Brachiosaurus (say BRAK-ee-oh-SAW-rus)

Brachiosaurus lived about 150 to 145 million years ago in the Late Jurassic period. Its name means 'arm reptile', because its front legs are much longer than its back legs.
Brachiosaurus was a dinosaur in the group known as sauropods. It was about 25m long and about 13m high. It was able to eat from the tallest trees, feeding on leaves and fruit with its chisel shaped teeth.

Brachiosaurus was one of the biggest land animals ever, probably weighing about 80 tonnes. Good fossils have been found in Colorado, USA and Tanzania.

4.   Diplodocus (say dip-LOD-oh-kus)

The name means 'double beamed lizard' because it had extra bones to help support its spine.

Diplodocus lived about 150 to 145 million years ago in the Late Jurassic period. It was part of the group of dinosaurs known as sauropods. The Late Jurassic period was a time when there were many sauropods.

Diplodocus was a 'lizard-hipped' dinosaur that was about 45 metres long. Much of its length was the tail, which flicked like a whip. Diplodocus weighed about 30 tonnes. Its height at the hips was about 5 metres. It was the longest of the dinosaurs, but not the heaviest. Its brain was not much larger than a tennis ball, but there were many nerves in the base of its spine. This was necessary for it to cope with such an enormous size and to control its tail and back legs.

Diplodocus was a herbivore. It had peg-like teeth which it used for stripping off soft leaves such as those of ferns. The teeth were not used for chewing however. Diplodocus swallowed stones which helped grind up food in its stomach. This habit is similar to that of modern birds.

Fossils have been found in the Rocky Mountains, Montana, Utah, Wyoming and Colorado in the USA.

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1. The Triassic Period

The Triassic Period

248 to 206 Million Years Ago

In many ways, the Triassic was a time of transition. It was at this time that the world-continent of Pangaea existed, altering global climate and ocean circulation. The Triassic also follows the largest extinction event in the history of life, and so is a time when the survivors of that event spread and recolonized.

The organisms of the Triassic can be considered to belong to one of three groups: holdovers from the Permo-Triassic extinction, new groups which flourished briefly, and new groups which went on to dominate the Mesozoic world. The holdovers included the lycophytes, glossopterids, and dicynodonts. While those that went on to dominate the Mesozoic world include modern conifers, cycadeoids, and the dinosaurs.

Climate and Geography During the Triassic period, all of the earth's continents were joined together into a vast landmass called Pangaea (which was itself surrounded by an enormous ocean called Panthalassa). There were as yet no polar ice caps, and the climate was hot and dry, punctuated by violent monsoons.

Terrestrial Life The start of the Triassic period followed the Permian Extinction, an event of unknown cause that wiped out over two-thirds of land-dwelling vertebrates and 95 percent of ocean-dwelling species. Taking their place were the therapsids (mammal-like reptiles), archosaurs (from which the first dinosaurs like Herrerasaurus and Eoraptor evolved, as well as the first prehistoric crocodiles and pterosaurs), and primitive reptiles called pelycosaurs (the most famous of which was Dimetrodon). It was during the late Triassic period that the mammal-like reptiles evolved into the first mammals.



Eoraptor





Pelycosaurs

Pterosaurs



 Marine Life Because the Permian Extinction depopulated the world's oceans, the Triassic period was ripe for the rise of early marine reptiles like Placodus and Nothosaurus. The vast Panthalassan Ocean was soon restocked with new species of prehistoric fish, as well as simple animals like corals and cephalopods.

Avian Life Except for insects, the skies of the early Triassic period were relatively quiet. It was only toward the end of the Triassic that the earliest pterosaurs, such as Eudimorphodon, appeared on the scene, and they probably weren't the most accomplished fliers.

Plant Life The Triassic period wasn't nearly as lush and green as the later Jurassic and Cretaceous periods, but it did see an explosion of various land-dwelling plants, including cycads, ferns, and Gingko-like trees. Part of the reason there were no enormous dinosaurs during the Triassic (along the lines of Brachiosaurus) is that there simply wasn’t enough vegetation to nourish them

Some Dinosaurs of the Triassic Period

Coelophysis

(say SEE-low-FY-sis)
The name refers to its hollow bones.
Coelophysis lived 220-200 million years ago during the late Triassic Period. It was about 1 to 3 metres long and weighing about 30 kg.

It had a long slender neck. Coelophysis had a double hinged lower jaw, so that it could cut prey with a sawing action if necessary. Its jaws had lots of small, sharp teeth indicating that it was a carnivore. It possibly even ate other Coelophsis. It was built for speed.

In 1947, hundreds of Coelophysis skeletons were discovered buried together in New Mexico. Paleontologists believe they probably died in a flash flood.

2. Plateosaurus

(say PLAT-ee-oh-SAW-rus)
It lived about 22 to 215 million years ago in the Late Triassic period. Its name means 'Flat lizard'.

Plateosaurus belonged to a group of dinosaurs known as prosauropods which was related to the sauropods of the Jurassic and Cretaceous periods.

Plateosaurus was a 9 metre long herbivore weighing about 4 tonnes. It was about 4 metres tall. It evolved in the Late Triassic period and lived up till the Early Jurassic period.

It was the first of the giant dinosaurs to feed only on plants and the first to be able to feed on vegetation in trees by evolving a long neck. It had long back legs and a long tail. Its mouth was like a beak but had teeth. It walked on four legs but probably stood on its back legs and grabbed branches with the claws on its front legs as it fed on leaves. Palaeontologists believe that they may have lived in herds.

Fossils have been found in Germany, France and Switzerland

3. A flying reptile of this period: Peteinosaurus

(say pet-INE-oh-SAW-rus)
The name means 'Winged lizard'. It was not a dinosaur, but a flying reptile living at the same time.It lived about 222 to 215 million years ago in the Late Triassic period

It was an early pterosaur, or flying reptile, with a wingspan of about 60 cm across. It weighed about 100 grams.

Peteinosaurus had very light bones. It had sharp, cone-like teeth. It caught and ate insects as it flew. It had a long finger on its hand, and skin stretched from this to its foot to form a wing on either side. The wings were attached to the body and thigh. The straight tail was about 20 cm long, and was used to steer when it was flying.

Peteinosaurus is one of the earliest vertebrates to be able to fly rather than glide. Complete fossils were found in Cene, in the Italian Alps

4. Fleeing Nothosaurs

An artist's rendering shows hatchling nothosaurs heading for the safety of water as a hungry but terrestrial Ticinosuchus attacks near a lagoon in ancient Switzerland. Nothosaurs lived during the mid- and late Triassic period and were among the earliest reptiles to take to the sea. Because nothosaurs may have had to come ashore to lay eggs, the eggs and hatchlings would have been vulnerable to Ticinosuchus. Yet once the hatchlings reached deeper waters, they were safe—for the moment.

5. Herrerasaurus

An artist's depiction shows a Herrerasaurus lurking in a forest in what is now Argentina as smaller animals hide in the undergrowth. Herrerasaur fossils are among the oldest ever discovered, dating back about 228 million years to the mid-Triassic.