Dinosaurs

Dinosaurs are known to almost everybody. These extinct beasts fascinate even little kids. They were the ones that ruled in the Age of Reptiles.

Here is a brief explanation of the groups of dinosaurs. After every group there are a few species listed in brackets for those of you who want a more thorough look. Dinosaurs are divided into two main groups (orders):

Saurischia:

Sauropods were large herbivores on four legs. The sauropods, which included Apatosaurus (Brontosaurus), Diplodocus, and Brachiosaurus. Brachiosaurus was among the largest land animals ever to live. It was 80 feet (24 meters) long and weighed up to 50 tons. It could eat the branches of trees that were 40 feet in the air. Diplodocus was 90 feet long. [Apatosaurus (Brontosaurus), Diplodocus, Brachiosaurus, Barosaurus]

Theropods were the meat-eating dinosaurs. They were divided into two groups, also.

Carnosaurs were the ones that terrorized all other groups. The most famous of this group was Tyrannosaurus Rex, who had serrated teeth the length of toothbrushes, and it was 52 feet long. [Tyrannosaurus Rex, Allosaurus, Tarbosaurus, Gorgosaurus]

Coelurosaurs were small, nimble carnivores that probably lived on insects, lizards, and meat that was left over from their larger cousins. Coelurosaurs resembled ostriches. They had long skinny legs like skewers and a beaked head atop a long neck. [Celophysis, Ornitholestes, Ornithomimus]

Ornithischia:

A major group in this order was the Ornithopods. These were mostly bipeds at first, like Iguanodon. Iguanodon had large spikes instead of thumbs, probably used for defense or foraging. All Ornithopods (and all Ornithischia) were herbivores. [Heterodontosaurus, Lycorhinus, Camptosaurus, Iguanodon] The early Ornithopods evelved into two groups:

The Hadrosaurs lived during the late Cretaceous. These have been given the nickname "duck bills" because of their mysteriously shaped mouths. They looked like flat, toothless beaks. But what was even more interesting was the rest of the head. It had a crest, which was a long nose-bone, sticking out on top of the head. Several different shapes and sizes of these crests existed. Scientists are puzzled by the use of these. Samples of Hadrosaurs have even come with intact skin, so we know almost exactly how they looked like. [Anatosaurrus, Lambeosaurus, Saurolophus, Parasaurolophus, Corythosaurus]

Ceratopians, or horned dinosaurs, also evolved from the Ornithopods. This group contains another very famous dinosaur - Triceratops. Triceratops had three horns on its head and a bony ruffle covering its neck. These Ceratopians are much like the modern Rhinoceros - big and powerful with a horn on top. The largest Ceratopians weighed 8 tons, but the smaller ones, like Protoceratops, were not quite so grand. [Protoceratops, Triceratops, Chasmosaurus, Monoclonius, Styracosaurus]

Another Ornithischia group was the Stegosaurus. Needing to adapt because of its lack of speed, the famous Stegosaur Stegosaurus developed large spikes on its tail and upright armor plates on its back. Even with this display of defense, the Stegosaurs died out by the end of the Jurassic [Stegosaurus]

Ankylosaurs were the tanks of the Cretaceous. On their tails, they had large clubs or spikes to defend themselves. On their backs, they had armor, spikes, and hard leathery skin. [Ankylosaurus]

For whatever reason, dinosaurs died out at the end of the Cretaceous. Although no one knows yet why this happened, the general scientific populace supports the theory that there was a climate change on earth that the creatures could not adapt to. It is a mystery, though, how this occurred.

The most supported theory is that of a large meteor hitting the earth, spewing dust and debris into the air. This would block sunlight, causing a cooling in the earth's climate. In turn, cold-blooded animals would die out. In recent years, scientists have found a possible crash site off the Yucatan Peninsula in Mexico.

Another climatic change theory is one where volcanoes spit out a lot of dust, also blocking the sun.

Other explanations exist:

A tremendous increase in solar radiation.

A reversal of the earth's magnetic field.

Plants turned alkaline, and dinosaurs could not survive on them.

A Black Death swept the land.

Egg-eating mammals swiped the dinosaur's eggs.

Some of these though, cannot be proven, and some do not account for reductions in the waters and skies. And why didn't mammals, crocodiles, and birds die out? This extinction remains somewhat of a mystery.

Sauropods

Carnosaurs

Hadrosaurs (Parasaurolophus)

Ceratopians

The most supported theory of extinction is a comet impact.

Mesozoic Era: Creature Feature

Dinosaurs are known to almost everybody. These extinct beasts fascinate even little kids. They were the ones that ruled in the Age of Reptiles. Here is a brief explanation of the groups of dinosaurs. After every group there are a few species listed in brackets for those of you who want a more thorough look. Dinosaurs are divided into two main groups (orders): Saurischia: Sauropods were large herbivores on four legs. The sauropods, which included Apatosaurus (Brontosaurus), Diplodocus, and Brachiosaurus. Brachiosaurus was among the largest land animals ever to live. It was 80 feet (24 meters) long and weighed up to 50 tons. It could eat the branches of trees that were 40 feet in the air. Diplodocus was 90 feet long. [Apatosaurus (Brontosaurus), Diplodocus, Brachiosaurus, Barosaurus] Theropods were the meat-eating dinosaurs. They were divided into two groups, also. Carnosaurs were the ones that terrorized all other groups. The most famous of this group was Tyrannosaurus Rex, who had serrated teeth the length of toothbrushes, and it was 52 feet long. [Tyrannosaurus Rex, Allosaurus, Tarbosaurus, Gorgosaurus] Coelurosaurs were small, nimble carnivores that probably lived on insects, lizards, and meat that was left over from their larger cousins. Coelurosaurs resembled ostriches. They had long skinny legs like skewers and a beaked head atop a long neck. [Celophysis, Ornitholestes, Ornithomimus] Ornithischia: A major group in this order was the Ornithopods. These were mostly bipeds at first, like Iguanodon. Iguanodon had large spikes instead of thumbs, probably used for defense or foraging. All Ornithopods (and all Ornithischia) were herbivores. [Heterodontosaurus, Lycorhinus, Camptosaurus, Iguanodon] The early Ornithopods evelved into two groups: The Hadrosaurs lived during the late Cretaceous. These have been given the nickname "duck bills" because of their mysteriously shaped mouths. They looked like flat, toothless beaks. But what was even more interesting was the rest of the head. It had a crest, which was a long nose-bone, sticking out on top of the head. Several different shapes and sizes of these crests existed. Scientists are puzzled by the use of these. Samples of Hadrosaurs have even come with intact skin, so we know almost exactly how they looked like. [Anatosaurrus, Lambeosaurus, Saurolophus, Parasaurolophus, Corythosaurus] Ceratopians, or horned dinosaurs, also evolved from the Ornithopods. This group contains another very famous dinosaur - Triceratops. Triceratops had three horns on its head and a bony ruffle covering its neck. These Ceratopians are much like the modern Rhinoceros - big and powerful with a horn on top. The largest Ceratopians weighed 8 tons, but the smaller ones, like Protoceratops, were not quite so grand. [Protoceratops, Triceratops, Chasmosaurus, Monoclonius, Styracosaurus] Another Ornithischia group was the Stegosaurus. Needing to adapt because of its lack of speed, the famous Stegosaur Stegosaurus developed large spikes on its tail and upright armor plates on its back. Even with this display of defense, the Stegosaurs died out by the end of the Jurassic [Stegosaurus] Ankylosaurs were the tanks of the Cretaceous. On their tails, they had large clubs or spikes to defend themselves. On their backs, they had armor, spikes, and hard leathery skin. [Ankylosaurus] For whatever reason, dinosaurs died out at the end of the Cretaceous. Although no one knows yet why this happened, the general scientific populace supports the theory that there was a climate change on earth that the creatures could not adapt to. It is a mystery, though, how this occurred. The most supported theory is that of a large meteor hitting the earth, spewing dust and debris into the air. This would block sunlight, causing a cooling in the earth's climate. In turn, cold-blooded animals would die out. In recent years, scientists have found a possible crash site off the Yucatan Peninsula in Mexico. Another climatic change theory is one where volcanoes spit out a lot of dust, also blocking the sun. Other explanations exist: A tremendous increase in solar radiation. A reversal of the earth's magnetic field. Plants turned alkaline, and dinosaurs could not survive on them. A Black Death swept the land. Egg-eating mammals swiped the dinosaur's eggs. Some of these though, cannot be proven, and some do not account for reductions in the waters and skies. And why didn't mammals, crocodiles, and birds die out? This extinction remains somewhat of a mystery.	Sauropods
	Carnosaurs
	Hadrosaurs (Parasaurolophus)
	Ceratopians
	The most supported theory of extinction is a comet impact.