The History Of Dinosaurs


The dinosaurs were reptiles that appeared about 230 million years ago. It's believed that they
had scaly skin and some ate plants and others ate meat. Scientists don't know whether or not the
dinosaurs were cold blooded, but they think the smaller ones were warm blooded, and the large
ones were cold-blooded. In this report you'll learn about the earliest dinosaurs, the kinds of
dinosaurs, and how the dinosaurs died.

There are two main groups of the earliest dinosaurs: Thesaurischian, and the ornithischian

First I'll tell you about the Saurischian. The Saurischian were the first main group of dinosaurs.

The Saurischian had lizard like hip joints. In this group there is the Theropoda. These weird
dinosaurs were meat eaters that walked on their hind legs. Also there was the Sauropoda. The

Sauropoda were the plant eating dinosaurs that walked on all four legs.

The second main kind of dinosaurs were the Ornithischian, which had bird like hip joints. There
is only one group belonging to this group and that is the ornithopoda. The Ornithopoda were
plant-eating dinosaurs that walked on two legs. There were also the armored and horned
dinosaurs, which were also plant eaters.

There were many, many different kinds of dinosaurs. Some of them are the Brachiosaurus, the

Stegosaurus, the Triceratops, the Tyrannosaurus, and the Zizhongosaurus.

All of the dinosaurs are in one of two major groups. Plant eaters or meat eaters. Some plant
eaters are the Saltasaurus, the Kritosaurus, and the Datousaurus. Some Meat eaters are the

Chilantaisaurus, the Poekilopleuron, and probably the most terrifying one of all, the

Tyrannosaurus.

During the Carboniferous Period (360 to 286 million years ago), dense tropical forests were concentrated along the equator. Decaying vegetation, compressed by overlying deposits of sand and mud, was gradually converted into coal. Coal deposits of Illinios, the Appalachians, Britain and Germany were originally formed in a continuous band which was dispersed when the continents drifted apart.

The Mesozoic Era lasted from 245 until 65 million years ago. In the sea, marine communities began to assume a modern composition of molluscs and other invertebrates. On land, dinosaurs dominated faunas, and the first flowering plants appeared. At the beginning of the Mesozoic, all of the earth's continents were joined as the supercontinent Pangea.

Some dinosaurs can swim and some can fly. The ones that swim have large, flat arms, or
flippers, that help them through the water. The ones that fly usually have two legs and huge
wings that can have a 30 foot wingspan!

There are many theories about how the dinosaurs died. The most populaur one is that the
weather became cooler, and the dinosaurs had no feathers or fur to protect them against the
changing weather. Others are like a star exploded, but then how could some other speacies have
lived. Another one is that an astioriod hit the earth and made the land dark for three, or so ,
years. So only the animals that could live on nuts or rotten plants could live. They also think that
they have the rock.

The dinosaurs came to rise in the earlier part of the Triassic period, and ecologically dominated
our planet until the late cretaceous. Dinosaurs evolved from reptiles, and birds evolved from the
dinosaurs (to clear up an erroneous myth circulating out there, the dinosaurs did not evolve into
birds. The birds came from the dinosaurs).

Dinosaurs have been divided into two main groups:

Saurischians, or "lizard-hipped" dinosaurs, and Ornithchians, or "bird-hipped" dinosaurs

Saurischians, in my opinion, are the better of the two groups. They include all dinosaurian
predators and the sauropods, or animals such as Apatosaurus and other very large animals. The
ornithchians essentially include everyone else; Triceratops, Stegosaurus, Ankylosaurus, and all of
the other herbivores.

The saurischians are divided further into the theropods (animals that walked on two feet), and
the sauropods, as mentioned above. Further information about these animals can be found in
my two dinosaur databases, below. By now, most people are beginning to believe that dinosaurs
were warm-blooded. Others believe that the dinosaurs were cold-blooded, and then there is the"muddy middle", or those who believe that the dinosaurs were some of both. This is known as
the endo-ecto question, which asks whether the dinosaurs were endotherms (warm-blooded) or
ectotherms cold-blooded. Both viewpoints have very competitive arguments and are still being
debated among paleontologists. By 136 million years ago, the end of the Jurassic period and the
beginning of the Cretaceous, the break-up of Pangea was well underway. North America and

Eurasia had begun to separate as had South America and Africa.

Dinosaurs still dominated the land but by the end of the Cretaceous they would be wiped out by
another mass extinction. By the middle of the Cretaceous flowering plants had developed
and began to dominate other forms of plant life.

One of the great mysteries in science is the extinction of the dinosaurs at the end of the

Mesozoic Era some 65 million years ago. Who or more likely what caused it is unknown and a
subject of great debate.

Scientists believe that climatic changes might be responsible for most of these extinctions. There
is evidence that shows the temperature dropped at the end of the Mesozoic and the sea levels
fell. A sudden change in climate might affect the growth of plants and the dinosaur's food supply.

One of the most intriguing theories suggested for dinosaur extinction is the asteroid theory. In
the 1980's the father-son team of Luis and Walter Alvarez discovered a layer of Iridium in the

Cretaceous-Tentiary boundary. Iridium is rare on Earth, but abundant in meteorites. The

Alvarezs' suggested that a huge asteroid or comet, perhaps miles in diameter, hit the Earth at
that time. The result of such an impact would be an enormous explosion that would throw dust
clouds into the sky darkening the planet. Massive forest fires, triggered by the hit, would add
smoke to the sky. This would cool the planet causing the climatic changes observed.

A crater, now worn down and partly under the ocean, was found along the Mexican Yucatan

Peninsula. It's appearance coincides nicely with the Cretacious-Tertiary boundary. NASA
scientists estimate that the asteroid that struck would have been about 6 to 12 miles in diameter.

The Crater is about 130 miles across.

Triceratops was the three-horned ceratopsian dinosaur that was widespread in North America at the end of the Cretaceous Period. Its enormous frill, a modification of the bones from the rear part of the skull, included three horns that served to protect the front of the body. This peaceful plant eater was probably a mainstay in the diet of Tyrannosaurus.

Tyrannosaurus, the most famous of the carnivorous dinosaurs, weighed up to 7 tons. Its serrated, banana-sized teeth were used to crush the flesh and bone of its prey. With massive head and jaws that measured more than 5 feet in length, and a body length of up to 50 feet, adult tyrannosaurs were the largest of the predatory dinosaurs. They were also the last, living only at the very end of the Cretaceous Period, 65 million years ago.

Brachiosaurus was the largest and heaviest dinosaur known from the Morrison Formation of Utah. This supergiant weighed as much as 80 tons, or the combined weights of 15 large elephants. Ultrasaurus, a supergiant from the Morrison Formation of Colorado that is probably a species of Brachiosaurus, may have weighed as much as 100 tons. Brachiosaurus is the giraffe-necked sauropod, with tall front legs and a long neck designed to reach far above the ground. Bones of this Late Jurassic giant have also been found in eastern Africa.

Stegosaurus, the plated dinosaur, was one of the major plant-eaters of the Jurassic Period. Most paleontologists believe its triangular bony plates were set in two rows along the backbone in a staggered arrangement. The function of the plates is controversial. Perhaps they were for protection, but some paleontologists think that they may have collected solar radiation for thermal regulation.

Hadrosaurs, are two subfamilies of hadrosaurs, the Lambeosaurinae, which have a crest on the skull (like the skull on the right at the top of the page), and the Hadrosaurinae, which lacked the crest (like the skull at the left). The crest on a lambeosaur's skull contains the nasal passages, which "looped" through the crest and often formed sizeable chambers before passing into the airway.

Parasaurolophus, is extremely rare and is known from less than six specimens, making it more rare than Tyrannosaurus rex. Parasaurolophus lived during the Late Cretaceous, about 75 million years ago. Parasaurolophus belongs to a group of plant-eating dinosaurs known as hadrosaurs, or duck-billed dinosaurs. Some hadrosaurs, including Parasaurolophus, are noted for unusual nasal cavities that are expanded into head crests. Many of these crests took on truly bizarre shapes.

Utahraptor, was about 20 feet long and weighed about half a ton. It lived during the Late Early Cretaceous period, about 125 million years ago. It was a meat-eater and used its large, razor-sharp claws to cut into its prey.

Dinosaurs varied greatly in size, ranging in weight from 4 to 6 pounds , in the case of Compsognathus, and up to 160,000 pounds, in the case of Brachiosaurus. Dinosaurs have traditionally been assumed to have been cold-blooded, but in recent years, several different lines of evidence have been interpreted as indicating that dinosaurs may have been warm-blooded like birds and mammals.

The reproductive means of most dinosaurs is unknown, however fossils of dinosaur eggs have been discovered in Brazil, portugal and Tanzania, as well as the United States.

Dinosaur diets varied greatly. Many, including some of the largest species, were herbivores, consuming vast quantities of vegetation to sustain their large bodies. Some, such as the great Tyrannosaurus rex, were carnivores, preying voraciously on other Dinosaurs and keeping primitive mammals small and insignificant. Although Dinosaurs reigned for around 140 million years, their extinction is theorized to have come suddenly. Many scientists insist that an astroid that hit the Earth caused an enormous cloud of dust, striking at the food chain. By killing many plants, this asteroid may have doomed the Dinosaurs.

In 1990 a scientist called Alan Hildebrand was looking over some old geophysical data that had been recorded by a group of geophysicists searching for oil in the Yucatan region of Mexico. Within the data he found evidence of what could have been an impact site. What he 'found' was a ring structure 180km in diameter which was called Chicxulub. The location of this structure was just off the northwest tip of the Yucatan Peninsula. The crater has been dated (using the 40Ar/39Ar method) as being 65 million years old. The size of the crater is comparable to that which would have been caused by an impacting body with a diameter of roughly 10km.So we now have some of the proof of the asteroid theory. We know that a chondritic meteorite with a diameter of 10km contains enough iridium to cause a spike. We also know that about 65 million years ago there was an impact of a large object. The big question is what were the results, and how did they effect the dinosaurs.

The impact basin is buried by several hundred meters of sediment, hiding it from view. This image shows the basin viewed obliquely from approximately 60 above the surface looking north, with artificial lighting from the south.

The Cenozoic Era, which began 65 million years ago and continues today, is characterized by the evolutionary radiation of mammals and birds. The continents have slowly drifted apart through Cenozoic time to assume their current positions.