3 Types of Dinosaurs and Their Many Subtypes

Silhouette of three dinosaurs at sunset — Sauropods, theropods, Archaeopteryx, oh my! artpartner-images / Getty Images

While there are too many famous dinosaur species to keep track of — and potentially more types of dinosaurs to be discovered — the paleontologist Harry Govier Seeley split dinosaurs into two major dinosaur groups: the order Saurischia ("lizard-hipped" dinosaurs) and the order Ornithischia ("bird-hipped" dinosaurs).

Both orders probably had a common ancestor that lived sometime during the Middle Triassic.

Structural Differences Between Dinosaurs

As in all land animals, there were three bones in each side of the pelvis. The left and right ilia (singular: ilium) firmly gripped the spine in the sacrum. The left and right pubes (singular: pubis) extended down beneath the ilia. The left and right ischia (singular: ischium) extended down and back beneath the ilia and behind the pubes.

The top pelvis is typical for an ornithischian, or "bird-hipped," dinosaur. The bottom is typical for a saurischian, or "lizard-hipped," dinosaur.
Collection of Publications International, Ltd.

In some dinosaurs, the pubes extended down and forward, as they do in lizards. This is why Seeley called them saurischian or "lizard-hipped" dinosaurs. In other dinosaurs, the pubes extended down and back, running beneath and parallel to the ischia, as they do in modern day birds. Seeley called these dinosaurs ornithischian or "bird-hipped" dinosaurs.

Sauropod Dinosaurs

The sauropodomorphs quickly evolved into two major groups, the Prosauropoda and the Sauropoda. Although prosauropods appeared earlier, no known prosauropod could have been the ancestor of the sauropods.

There's copious fossil evidence documenting the dinosaur bones of all these sauropods. The fossilized remains of Megalosaurus were among the first extinct dinosaurs discovered in the 19th century as paleontology became a common practice.

Prosauropods

The prosauropods were widespread and had at least seven families. They lived until the Early Jurassic period.

The largest prosauropods, some as long as 40 feet (12.2 meters) or more, were straight-limbed dinosaurs that resembled the later sauropods in some ways. All prosauropods were herbivorous dinosaurs.

Thecodontosauridae: The most primitive prosauropod, Thecodontosaurus, was also one of the smallest. It was about 6 to 10 feet (1.9 to 3.1 meters) long. Like all prosauropods and most sauropods, it had a prominent claw on each front foot and a large claw on each back foot.
Plateosauridae: This is the best-known family of prosauropods, with animals found in Europe, China and North and South America. They were 25 to 30 feet (7.6 to 9.1 meters) long with long, narrow snouts, long necks, powerful front and back limbs, and heavy bodies.

Sauropoda

*Omeisaurus tianfuensis*, family *Euhelopodidae*.
Brian Franczak

The second group of sauropodomorphs, the Sauropoda, probably came from an ancestor much like Thecodontosaurus. This probably happened sometime in the Late Triassic, when sauropods first appeared. All sauropods were giants and four-legged plant-eaters.

Like today's elephants, sauropods had little fear of predators because of their size. Being large also helped them reach food, such as leaves in treetops, that was too high for smaller plant-eaters. Sauropods had many features because of their large size.

Vulcanodontidae: The earliest true sauropod is Vulcanodon from the Early Jurassic of Zimbabwe. The only skeleton is missing the head, neck and much of the tail. It had a bulky body and its legs were long and straight. The front limbs were almost as long as the back, and each back foot had five toes.
Barapasauridae: The next most primitive sauropod, Barapasaurus, is known from parts of several skeletons from the Early Jurassic of India. It was up to 60 feet (18.3 meters) long, with a slender body and a long neck, tail and limbs.

Euhelopodidae: Most of the sauropods known from the Middle and Late Jurassic of China are now placed in a separate family, the Euhelopodidae. Euhelopodids are one of the more primitive sauropod families, but they include such exotic animals as the extremely long-necked Mamenchisaurus and Omeisaurus. These dinosaur fossils are a sight to behold.
Cetiosauridae: This family is from the Middle Jurassic, perhaps from an ancestor from the Vulcanodontidae family. The cetiosaurids had expanded and spread into Europe, North and South America, Africa and Australia by the Middle Jurassic.
Brachiosauridae: The Brachiosaurus was among the largest land animals in history. To reduce weight, their huge vertebrae were almost completely hollow. Known worldwide, brachiosaurids appear in the fossil record during the Middle Jurassic, were most numerous in the Late Jurassic and almost vanished by the end of the Early Cretaceous.
Camarasauridae: In this family the skull was boxlike. They still had 12 neck vertebrae and the front limbs were slightly shorter than the back limbs. One of the last known camarasaurids was Opisthocoelicaudia from Mongolia, a heavy-bodied sauropod with a short tail that probably helped support it when it stood on its hind limbs to reach food.

Theropod Dinosaurs

From the smallest dinosaurs to the largest meat-eaters, the predatory theropod dinosaurs had the most different kinds of saurischian dinosaurs of all suborders. These two-legged meat-eaters had clawed feet with no more than three functional toes.

The wings and feet of birds are similar to the arms and feet of theropod skeletons. Also like birds, all theropods to some extent had hollow hones. The best ancestral bird is the small, feathered, theropod-like Archaeopteryx from the Late Jurassic.

Ceratosauria

Podokesauridae: The earliest ceratosaurians include Coelophysis from the Late Triassic of western North America. It was small and nimble and had a long, slender skull with many teeth.

Halticosauridae and Ceratosauridae: Dilophosaurus, which lived during the Early Jurassic, had a double crest on its head. Ceratosaurus was from the Late Jurassic and had a horn on its head. Both were from North America and are examples of later members of the ceratosaurians. After the Late Jurassic, ceratosaurians apparently vanished in the northern hemisphere but survived in South America.

Abelisauridae: The abelisaurids are a group of medium to large African and South American theropods characterized by short, tall skulls. Carnotaurus from Argentina and Majungatholus from Madagascar are similar with the exception that Carnotaurus has two large horns on the skull.

Tetanurae

The tetanurans, the most advanced theropods, included several dinosaur groups where the relationships are not well understood. Crests and other decorations on the head were usually not present. Their hands had three or fewer fingers, and the "thumb" usually had the largest claw.

*Abelisaurus comahuensis*.
Brian Franczak

Compsognathidae: The most primitive tetanuran was Compsognathus from the Late Jurassic of Europe. It was the smallest theropod, about 3 feet (0.9 meters) long and lightly built.
Coeluridae: Ornitholestes and Coelurus, which lived during the Late Jurassic in western North America, were fast-running, lightly built theropods that were 2 to 3 feet (0.6 to 0.9 meters) tall at the hips and from 6 to 10 feet (1.9 to 3.1 meters) long.
Carcharodontosauridae: This group of giant theropods from Gondwana includes enormous predatory dinosaurs, Giganotosaurus from Argentina and Carcharodontosaurus from North Africa.
Therizinosauridae: The therizinosaurids were apparently herbivorous or omnivorous theropods known from the Late Cretaceous of Asia and North America. The unusual, birdlike pelves and almost prosauropod-like skulls of therizinosaurids have resulted in uncertainty about their evolutionary position, but they have recently been shown to be theropods closely related to the Ornithomimidae.
Spinosauridae: Spinosaurids are a distinctive group of theropods with long, crocodile-like snouts and elongated vertebral spines that may have formed sail-like structures on their backs. Spinosaurids are restricted to the Cretaceous but have been identified in Africa, South America and Europe.
Oviraptorisauridae: Another curious theropod from the Cretaceous of Asia is Oviraptor, which has a tall, highly pneumatic skull with a turtle-like beak. Oviraptor got its name ("egg predator") because specimens were found in Mongolia with what were originally thought to be nests of ceratopsian eggs.
Allosauridae: This family is typical of the larger Jurassic and Early Cretaceous theropods that were from 15 to 35 feet (7.6 to 10.7 meters) long or longer. The biggest allosaurid may have been more than 40 feet (12.2 meters) long. Allosaurids were slender but dangerous predators.
Tyrannosauridae: Most dramatic of all the theropods were the tyrannosaurids, which probably came from allosauridlike ancestors at the beginning of the Late Cretaceous. The dreaded Tyrannosaurus rex was part of this family — and one of the last now-extinct non-avian dinosaurs to walk the Earth.

Tyrannosaurus attacks an Edmontosaurus
Canadian Museum of Nature

Ornithiscian Dinosaurs

The earliest ornithischian dinosaur was Pisanosaurus, a 3-foot-long (0.9-meters-long), two-legged (bipedal) plant-eater from the late Middle Triassic of Argentina. All ornithischians were plant-eaters.

Later ornithischians split into three advanced groups: heavy, armored plant-eaters that walked on all fours; specialized dome-headed dinosaurs and horned dinosaurs; and two-legged plant-eaters that included Iguanodon and duck-billed dinosaurs.

Stegosauridae: These armored dinosaurs probably evolved in China during the Early Jurassic. By the Late Jurassic, they were in Europe (Dacentrurus), North America (Stegosaurus) and Africa (Kentrosaurus).
Nodosauridae: The more primitive ankylosaurians — including all Jurassic and Southern Hemisphere genera — belong in this family. Some nodosaurids had large, cone-shaped spines along the neck and shoulders for protection.
Ankylosauridae: This family may have arisen during the Early Cretaceous from a nodosaurid ancestor. Ankylosaurid skulls had horns projecting from the back, giving them a triangular shape when viewed from above. All ankylosaurids had massive, bony tail clubs for defense.

Ceratopsia

The Ceratopsia were the horned dinosaurs and their relatives. They were different from the pachycephalosaurs (and all other dinosaurs) because they had a special bone, the rostral, which formed part of a large, parrotlike beak.

Psittacosauridae: The oldest and most primitive ceratopsians belong in this family of small, bipedal runners such as Psittacosaurus from the Early Cretaceous of China and Mongolia.
Protoceratopsidae: In this family, the back of the skull was expanded into a wide frill over the back of the neck. Microceratops was a bipedal animal, like its possible psittacosaurid ancestors. The other protoceratopsids walked on all fours, making their larger heads easier to support.
Ceratopsidae: The Ceratopsidae had the shortest range of any dinosaur family. They arose during the Late Cretaceous in western North America. They quickly evolved into many unusual forms and lived until the end of the Mesozoic Era. From cow to elephant size, the quadrupedal (four-legged) ceratopsids had horns and frills on their heads.

*Arrhinoceratops brachyops*.
Brian Franczak

*Heterdontosaurus tucki*.
Brian Franczak

Heterodontosauridae: These small, nimble, bipedal plant-eaters have been found mainly in Early Jurassic rocks of southern Africa. Their teeth were sharp and tusklike in front, but the teeth at the sides of the jaw were built for chewing and slicing plants.
Hypsilophodontidae: This was the most widespread and longest-lived ornithopod family. It flourished almost worldwide from the Middle Jurassic until the end of the Cretaceous. The Late Cretaceous Thescelosaurus grew to about 18 feet (5.5 meters) long.
Dryosauridae: This short-lived family arose about the same time as the Hypsilophodontidae. The earliest dryosaurid was Dryosaurus from the Late Jurassic of western North America and eastern Africa. Valdosaurus from the Early Cretaceous of Europe and northern Africa and Kangnasaurus from Africa are the other two genera in this family.
Camptosauridae: The Late Jurassic genus Camptosaurus from western North America was a chubby, medium-size ornithopod about 15 feet long. It had specialized feet and skull.
Iguanodontidae: Iguanodon is one of the best-known dinosaurs. This bulky, 35-foot-long ornithopod had a deep, narrow skull; a strong, well-developed pelvis; rows of bony tendons running along its back; a hand in which the thumb had become a sharp spike; and three broad toes plus an inner toe. They'd often walk on their hind legs.
Hadrosauridae: This group consists of two groups, the Hadrosaurinae and the Lambeosaurinae. They were both duck-billed dinosaurs that were closely related. They were large to very large plant-eaters of the Late Cretaceous in North and South America and Eurasia.