Dinosaurs are part of the animal kingdom, along with mammals, reptiles and birds. All living things are organized into groups based on how closely they are related to one another.
The lizard-hipped Sauropod dinosaur Diplodocus has a barrel-shaped body, long neck and whip-like tail, and walked on four trunk-like legs. Other sauropods were heavily armored such as Stegosaurus and Ankylosaurus, or had horns like Triceratops. Ornithischian dinosaurs such as Psittacosaurus had parrot-like beaks.
Age of Dinosaurs
Scientists divide dinosaurs into different classes, or dinosaur types. They do this based on things like what they ate or how they moved, whether they lived alone or in groups and so on. Meat-eaters walked on two legs and hunted for their food, while plant-eaters walked on four legs or used all eight to eat.
Hesperornis was a small plant-eater that probably roamed the forests of what is now Montana in the early Cretaceous period. A fossil of this creature was found in 1964, and it had a head the size of a tangerine or a dog's and a body the length of a modern car. Its brain, however, was only the size of a pea. This was one of the first dinosaurs to be discovered, and it shows us that the size of a dinosaur was not related to its brain.
A dinosaur that was more closely related to birds than any other was Archaeopteryx, which roamed the Mesozoic forests of what is now Germany. This dinosaur had feathers, a furcula (wishbone) and a fused collarbone that allowed for attachment of flight muscles. It was also a biped, which means it walked on two legs.
During the Jurassic and Cretaceous periods a group of dinosaurs developed that were herbivores. These were called ornithischians, a name that directly translates to "bird-hipped". The main group in this category was the stegosauria, which was known for the bony plates it had running down its back and pairs of spikes on its tail. The stegosauria included the well-known Stegosaurus and the more slender Hesperornis.
Another large herbivore of the Jurassic period was Plateosaurus, which stood about 25 feet tall and had a long neck and four sturdy legs. It was a member of the sauropod family, which also included the giant Apatosaurus and Barosaurus.
Another kind of dinosaur that is often classified as a meat-eater is Deinonychus, which was the largest carnivore that ever lived on Earth and is believed to have weighed more than 80 tons. This dinosaur had a large head, teeth and claws, which would have made it an effective predator of smaller dinosaurs and other creatures that lived at the time.
Dinosaur Shapes
The Tyrannosaurus rex is probably the dinosaur most of us have heard of. But that’s just the tip of the iceberg when it comes to dinos. There are hundreds of species to know about, and they come in all shapes and sizes.
Scientists group dinosaurs together based on their physical characteristics and how closely they are related to each other. This is called classification. All living things, including dinosaurs, are organized into groups that are referred to as kingdoms. Dinosaurs are in the Animal Kingdom, along with mammals, amphibians, reptiles and birds.
There are three major dinosaur types. Carnivores were meat-eaters, Herbivores were plant-eaters and Sauropods were large, bipedal herbivores that walked on two legs.
Carnivores were the first group of dinosaurs to appear and lived throughout the Mesozoic Era. The most recognizable dinosaurs in this group were the Tyrannosaurus, Velociraptor and Allosaurus. These ferocious creatures were carnivorous or meat-eaters and fed on other dinosaurs, animals, plants and sometimes even insects.
Herbivores were the second group to appear and they lived through the Jurassic and Cretaceous Periods. The most famous herbivore in this group is the Stegosaurus. This dinosaur had a long neck, which enabled it to reach tall trees to eat their leaves. It also had a beak, which could be used to break up large chunks of plant matter and it had teeth that were suited for chewing.
Sauropods were the largest of all dinosaurs and they lived through the Jurassic and the early part of the Cretaceous Period. They were quadrupeds, which means they walked on four legs. The most recognizable trait of sauropods was their long necks. These long necks allowed them to eat the foliage from trees and other vegetation, similar to how giraffes feed today. They were the most impressive of all dinosaurs, growing to be as long as a city bus!
Another branch of ornithischian dinosaurs were the thyreophorans. They were heavily armored with rows of bony plates running across their bodies. Some had spikes and tail clubs that they might have used to protect themselves from predators. Examples of this dinosaur type include Ankylosaurus and Stegosaurus.
Dinosaur Types
Dinosaurs were large reptiles that lived on land and ate meat, fish or plants. Some weighed 80 tons and were over 120 feet long. Some were as little as chickens, weighing as little as 8 pounds. Fossils of dinosaurs have been discovered all around the world. Most dinosaurs were plant-eaters, but a few were carnivores. Meat-eaters walked on two legs and hunted in groups. Plant-eaters walked on two or four legs and grazed on plants. The main feature that set dinosaurs apart from other reptiles is a hole in their hip socket which allowed them to walk upright. Pterosaurs (flying reptiles) and plesiosaurs (ocean-dwelling reptiles) did not have this feature, so they are not considered dinosaurs.
Scientists split dinosaurs into different groups based on what they looked like, how they moved and what they ate. This makes it easier to study and understand dinosaurs. It also helps when paleontologists find new dinosaur fossils because they can put them into one of the dinosaur groups based on how they look.
The first group is called Ornithischia which translates to “bird hip.” This includes Thyreophora, which include the armored dinosaurs Ankylosaurus and Stegosaurus and Ceratopsidae, which include Triceratops and Parasaurolophus. It also includes Aves, which include birds.
Another group is Saurischia, which translates to “lizard hip.” This includes Sauropods, which include the huge dinosaurs Tyrannosaurus and Giganotosaurus. It also includes Ornithomimus and Coelophysis, which are slender theropods that ate small animals.
The last group is Archosauropoda, which translates to “bird foot.” This includes Ichthyosaurs and Mosasaurus, which were fish-eating marine reptiles. It also includes Dimetrodon and pterosaurs, which are flying reptiles. These animals have feet with claws and lay eggs. They are the closest relatives of modern mammals. This is the only group of prehistoric animals to have a close relationship with living mammals.
Dinosaur Fossils
Scientists study fossils to determine what kinds of animals dinosaurs were. They were large reptiles, but they looked very different from modern reptiles and were clearly terrestrial (land-based). Their soft parts quickly decomposed, leaving hard parts like bones and teeth behind. Fossils show that dinosaurs held their limbs beneath their bodies in column-like fashion, much like modern elephants and other land mammals, rather than sprawling them sideways as lizards do. And their dinosaur skeletons were made of a strong, tough material called phosphate rock. Fossils of dinosaur limbs and other body parts are often very fragmentary, but they are enough to allow scientists to identify specific types of dinosaur. As more and better dinosaur fossils were discovered, the group of animals known as dinosaurs was refined. The general definition of dinosaur is based on many anatomical features, which are fairly rare or unique among reptiles.
During the late Jurassic and early Cretaceous periods, a new type of dinosaur evolved from an existing species. This bird-like dinosaur, the first avian dinosaur, became the forerunner of all birds. All non-avian dinosaurs then went extinct.
There are now about 1,545 scientifically described dinosaur species. And each year, paleontologists discover about 50 previously unknown dinosaurs.
Most dinosaurs were herbivorous, but a few were carnivorous or omnivorous. Dinosaur skeletons are found in a wide variety of environments, from mountains to seas to rivers and lakes. These fossils have allowed scientists to reconstruct the appearance of specific dinosaurs and understand their habits.
The major groups of dinosaurs are ornithischians, sauropodomorpha and theropoda. Ornithischians included beaked plant-eaters such as Stegosaurus and duck-billed dinosaurs (also called hadrosaurs). They also include horned dinosaurs like Triceratops and a number of armored dinosaurs, such as Ankylosaurus.
Sauropodomorpha includes long-necked pot-bellied dinosaurs such as Diplodocus, their smaller antecedents and extra-large sauropods, including the enormous Dreadnoughtus and Argentinosaurus. These dinosaurs were mostly meat-eaters, but a few — such as Chilesaurus diegosuarezi — were primarily herbivorous.
Theropods were a group of large meat-eating dinosaurs, including the Tyrannosaurus and Velociraptor. They were probably the most powerful predators on Earth. Some theropods, such as Deinonychosauria and Oviraptorosauria, were largely herbivorous or omnivorous.
