They where living creatures who lived in prehistoric times. Giants, Monsters, Beasts are words to describe them.

Dinosaurs (or the dinosauria) are a group of archosaurian reptiles that first appeared about 230 million years ago, during the Triassic Period of the Mesozic era. Many groups went extinct at the end of the Cretaceous, about 65 million years ago. Birds are their only living descendants, and are often referred to as 'avian dinosaurs'.

Despite the name dinosaur meaning "terrible lizard" the dinosauria are not lizards. Dinosaurs are classified as archosaurians, a group which includes crocodilians and possibly pterosaurs.

Definitionally speaking, Dinosaurs might be defined in several ways and the most common way is nodular, that is defining a particular antecedent to all dinosauria. The most common definition is therefore phylogenic and not linnean and therefore includes birds categorically. Dinosauria = df. any descendant of the most recent common ancestor of Triceratops (the most commonly selected ornithischia) and Quiscalus (or any other arbitrary genus of theropod. Tyrannosaurus is common and the suborder neornithes is common. I just chose this genus of "grackles" here but whatever is chosen within those parameters leads to the same encompassing categorical definition of Dinosauria.). Another common way to distinguish dinosaurs from other archosaurs is by a particular arrangement of the ankle bones astragalus and calcaneum and how those bones orientated in respect to one another and with the fibula.

The pelvic structures separated dinosaurs into two orders: saurischia and ornithischia. Saurischians include the prosauropods, sauropods, theropods. Ornithischians include ornithopods hadrosaurs, ankylosaurs, stegosaurs and ceratopsians.

The earliest dinosaurs were usually small in size, and they slowly evolved into different species and a variety of different ecological niches, including herbivores, carnivores and omnivores. Ancestrally all dinoaurs were bipedal but some of the herbivorous groups evolved quadrupedalism, such as the sauropods, hadrosaurs, ankylosaurs and ceratopsians. Many were covered in scales and at some point in their evolutionary history they evolved feathers. One branch of feathered dinosaurs eventually evolved wings, flight and eventually lead to birds. Whilst most mesozoic dinosaurs could probably swim to some degree very few (Hesperornithes) have evidence to suggest they lived aquatic lifestyles. There are modern day birds, such as ducks and penguins, that live in or around water.

Some dinosaurs were the largest terrestrial animals ever to have lived, such as the sauropods, Argentinosaurs, Puertasaurus and Alamosaurus. The specimens that represent these dinosaurs are incomplete, so estimates for their dimensions vary in certainty. Some sauropods had the longest necks of any animals with some reaching 13 or more meters in length. One of the longest dinosaurs was Supersaurus (estimated at 33-34 metres long) and one of the tallest was possibly Sauroposeidon (estimated at 17 metres high). Most of the smallest known dinosaurs belong in the theropod group Maniraptoria which includes modern day birds. The smallest living dinosaur is the 'Bee Hummingbird'

Many types of dinosaurs went extinct at the end of the Cretaceous Period, around 65 million years ago. There is large body of evidence that an asteroid several miles wide crashed onto Earth which may have triggered the mass extinction 65 million years ago. Other evidence suggests that volcanic activities and climate change could have played a role in the mass extinction also.

The only group of dinosaurs to survive the mass extinction and live on to the present are birds.

It's a common misconception the flying pterosaurs and the aquatic plesiosaurs are dinosaurs. The fossil record for pterosaur evolution isn't fully understood but most researchers don't consider them dinosaurs. Although they may be closely related. The plesiosaurs are not closely related to dinosaurs.

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There were many types, the most famous of which was the Tyrannosaurus Rex. They were sorted into two groups; Ornischthia (bird hipped) and Sauischthia (lizard hipped).

A dinosaur is an exint gaint reptile that lived over a million years ago.

Answer2: Before 1824, dinosaurs were unknown to man. In that year the bones of several kinds of fossilized reptiles were unearthed in England. British paleontologist Richard Owen called these animals Dinosauria, from the two Greek words deinos and sauros, meaning "terrible lizard." The name remains in common use to this day, although while dinosaurs are reptiles, they are not lizards.

Since 1824, dinosaur fossils have been found on every continent. The fossil record, left in layers of sedimentary, or water-laid, rock, indicates that there was an extraordinary abundance and variety of dinosaur types at a time in earth's history called the Age of Dinosaurs. Some made their home on land, while others lived in swamps. Some perhaps even lived in water, much like the present-day hippopotamus.

Large quantities of dinosaur remains-including such nonskeletal evidence as tracks-have been unearthed in the Great Central Plain of North America. The prairies of central Alberta have yielded many dinosaur remains, including nearly 500 complete skeletons. In the 1920's, expeditions discovered dinosaur bones in the Gobi Desert of central Asia. In the 1940's a Soviet expedition in Mongolia discovered a dinosaur skeleton some 40 feet [12 m] in length.

In 1986 Argentine scientists discovered the fossils of a plant-eating dinosaur in Antarctica. Until then, Antarctica had been the only major land area where dinosaur fossils had not been found. Just before that, an American researcher found dinosaur bones on the North Slope of Alaska. Throughout the last hundred years, deposits of dinosaur bones have been uncovered in so many places that it has become apparent that dinosaurs were widespread in the remote past.

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