Dinosaur fossils have been found on all seven continents. All non-avian dinosaurs went extinct about 66 million years ago. There are roughly 700 known species of extinct dinosaurs. Modern birds are a kind of dinosaur because they share a common ancestor with non-avian dinosaurs. The earliest dinosaurs for which we do have well-documented fossils are found in Late Triassic Ischigualasto Formation in northern Argentina. Skeletons discovered in these rock layers include the meat-eating dinosaurs Herrerasaurus and Eoraptor, as well as the plant-eating dinosaur Pisanosaurus.

The heaviest dinosaur was Argentinosaurus at 77 tonnes. It was the equivalent to 17 African Elephants. Argentinosaurus is a double award winner being also the longest dinosaur. It is also the largest land animal to have ever lived.

In 1677, Robert Plot is credited with discovering the first dinosaur bone, but his best guess as to what it belonged to was a giant human. It wasn't until William Buckland, the first professor of geology at Oxford University, that a dinosaur fossil was correctly identified for what it was.

Scientists already know that an asteroid—or perhaps a comet—struck Earth off Mexico's Yucatán Peninsula. The resulting 110 miles/80 kilometers wide Chicxulub crater is thought to have caused a decades-long “impact winter” that killed the dinosaurs.

While scientists have complex ways of classifying dinosaurs, most people separate them into three groups: carnivores, herbivores, and omnivores. Let's learn more about these three types of dinosaurs.

First Dinosaurs. Approximately 230 million years ago, during the Triassic Period, the dinosaurs appeared, evolved from the reptiles. Plateosaurus was one of the first large plant-eating dinosaurs, a relative of the much larger sauropods. It grew to about 9 meters in length. Dinosaurs lived on all of the continents.

At the beginning of the age of dinosaurs (during the Triassic Period, about 230 million years ago), the continents were arranged together as a single supercontinent called Pangaea. During the 165 million years of dinosaur existence this supercontinent slowly broke apart.

After the dinosaurs died out, nearly 65 million years passed before people appeared on Earth. However, small mammals (including shrew-sized primates) were alive at the time of the dinosaurs.

The short answer is we know of about 900 valid dinosaur species that existed. In 1841, Richard Owen, the first director of London's Natural History Museum, gave the name dinosaurs to these giant prehistoric reptiles. The word dinosaur is from the Greek deinos (terrible) and sauros (lizard).

After the dinosaurs' extinction, flowering plants dominated Earth, continuing a process that had started in the Cretaceous, and continue to do so today. But all land animals weighing over 25 kilogrammes died out. 'What we're left with are basically the seeds of what we have today.

Modern Dinosaur movies depicting the dinosaurs being created in lab by modern science. They are popular among peers as it contains something unlike our now existing animals. Curiosity drives people to research, learn and explore, while new concepts keep rising into this world.

The prehistoric reptiles known as dinosaurs arose during the Middle to Late Triassic Period of the Mesozoic Era, some 230 million years ago. They were members of a subclass of reptiles called the archosaurs (“ruling reptiles”), a group that also includes birds and crocodiles.

Scientists first began studying dinosaurs during the 1820s, when they discovered the bones of a large land reptile they dubbed a Megalosaurus (“big lizard”) buried in the English countryside. In 1842, Sir Richard Owen, Britain’s leading paleontologist, first coined the term “dinosaur.” Owen had examined bones from three different creatures–Megalosaurus, Iguanadon (“iguana tooth”) and Hylaeosaurus (“woodland lizard”). Each of them lived on land, was larger than any living reptile, walked with their legs directly beneath their bodies instead of out to the sides and had three more vertebrae in their hips than other known reptiles. Using this information, Owen determined that the three formed a special group of reptiles, which he named Dinosauria. The word comes from the ancient Greek word deinos (“terrible”) and sauros (“lizard” or “reptile”).

Since then, dinosaur fossils have been found all over the world and studied by paleontologists to find out more about the many different types of these creatures that existed.

Scientists have traditionally divided the dinosaur group into two orders: the “bird-hipped” Ornithischia and the “lizard-hipped” Saurischia. From there, dinosaurs have been broken down into numerous genera (e.g. Tyrannosaurus or Triceratops) and each genus into one or more species. Some dinosaurs were bipedal, which means they walked on two legs. Some walked on four legs (quadrupedal), and some were able to switch between these two walking styles.

Some dinosaurs were covered with a type of body armor, and some probably had feathers, like their modern bird relatives. Some moved quickly, while others were lumbering and slow. Most dinosaurs were herbivores, or plant-eaters, but some were carnivorous and hunted or scavenged other dinosaurs in order to survive. At the time the dinosaurs arose, all of the Earth’s continents were connected together in one land mass, now known as Pangaea, and surrounded by one enormous ocean. Pangaea began to break apart into separate continents during the Early Jurassic Period (around 200 million years ago), and dinosaurs would have seen great changes in the world in which they lived over the course of their existence. Dinosaurs mysteriously disappeared at the end of the Cretaceous Period, around 65 million years ago.

Many other types of animals, as well as many species of plants, died out around the same time, and numerous competing theories exist as to what caused this mass extinction. In addition to the great volcanic or tectonic activity that was occurring around that time, scientists have also discovered that a giant asteroid hit Earth about 65.5 million years ago, landing with the force of 180 trillion tons of TNT and spreading an enormous amount of ash all over the Earth’s surface. Deprived of water and sunlight, plants and algae would have died, killing off the planet’s herbivores; after a period of surviving on the carcasses of these herbivores, carnivores would have died out as well.

Despite the fact that dinosaurs no longer walk the Earth as they did during the Mesozoic Era, unmistakable traces of these enormous reptiles can be identified in their modern-day descendants: birds. Dinosaurs also live on in the study of paleontology, and new information about them is constantly being uncovered. Finally, judging from their frequent appearances in the movies and on television, dinosaurs have a firm hold in the popular imagination, one realm in which they show no danger of becoming extinct.

The Triassic, Jurassic, and Cretaceous periods were marked out by geologists to distinguish among various types of geologic strata (chalk, limestone, etc.) laid down tens of millions of years ago. Since dinosaur fossils are usually found embedded in rock, paleontologists associate dinosaurs with the geologic period in which they lived—for example, "the sauropods of the late Jurassic."

To put these geologic periods in the proper context, bear in mind that the Triassic, Jurassic, and Cretaceous don't cover all of prehistory, not by a long shot. First came the Precambrian period, which stretched from the earth’s formation to about 542 million years ago.

The development of multicellular life ushered in the Paleozoic Era (542–250 million years ago), which embraced shorter geologic periods including (in order) the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian periods. It's only after all that we reach the Mesozoic Era (250-65 million years ago), which includes the Triassic, Jurassic and Cretaceous periods.

Ages of the Dinosaurs (The Mesozoic Era)

This chart is a simple overview of the Triassic, Jurassic, and Cretaceous periods, all of which were part of the Mesozoic era. In brief, this incredibly long period of time, measured in "mya" or "millions of years ago," saw the development of dinosaurs, marine reptiles, fish, mammals, flying animals including pterosaurs and birds, and a huge range of plant life. The largest dinosaurs did not emerge until the Cretaceous period, which started over 100 million years after the start of the "age of dinosaurs."

... Triassic: 237–201 mya ...

Archosaurs ("ruling lizards");

therapsids ("mammal-like reptiles")

...Jurassic: 201–145 mya ...

Dinosaurs (sauropods, therapods);

Early mammals; Feathered dinosaurs

...Cretaceous : 145–66 mya ...

Dinosaurs (sauropods, therapods, raptors, hadrosaurs, herbivorous ceratopsians);

Small, tree-dwelling mammals

Archosaur: Sometimes called “ruling reptiles,” this group of ancient animals included dinosaurs and pterosaurs (flying reptiles)

Therapsid: A group of ancient reptiles that later evolved to become mammals

Sauropod: Huge long-necked, long-tailed vegetarian dinosaurs (such as the Apatosaur)

Therapod: Two-legged carnivorous dinosaurs, including raptors and Tyrannosaurus

RexPlesiosaur: Long-necked marine animals (often described as similar to the Loch Ness monster)

Pterosaur: Winged flying reptiles that ranged from the size of a sparrow to the 36-foot-long

QuetzalcoatlusCycad: Ancient seed plants that were common during the time of the dinosaurs and are still common today

Early estimates of 300-year lifespans for the largest sauropods were based on comparisons with crocodiles and turtles, which have much slower metabolisms. The consensus is now that Apatosaurus and Diplodocus dinosaurs probably only lived for 70 or 80 years, which is about the same as an elephant today.

The Struthiomimus may have been the fastest dinosaur. It could run up to 60 miles per hour!

Troodon had a large brain for its relatively small size and was probably among the smartest dinosaurs. Its brain is proportionally larger than those found in living reptiles, so the animal may have been as intelligent as modern birds, which are more similar in brain size.

The short answer is we know of about 900 valid dinosaur species that existed.