Types of Dinosaurs
Estimates vary, but in terms of extinct non-avian dinosaurs, about 300 valid genera and roughly 700 valid species have been discovered and named. However, given that the fossil record is incomplete, in the sense that scientists have yet to discover fossils of other kinds of dinosaurs that no doubt existed, these numbers do not reflect the true diversity of extinct dinosaurs.
One reason for the incompleteness of the fossil record is that rocks for some geologic time periods are not commonly found on the surface of the Earth. For example, many more kinds of Late Cretaceous dinosaurs are known than Middle Jurassic dinosaurs because outcrops of Late Cretaceous are more numerous and more widely spread geographically than those of Middle Jurassic age.
Dinosaurs are prehistoric reptiles that have lived on Earth from about 245 million years ago to the present. Modern birds are one kind of dinosaur because they share a common ancestor with non-avian dinosaurs.
Non-avian dinosaurs (all dinosaurs besides birds), which are now extinct, varied greatly in shape and size. Some weighed as much as 80 tons and were more than 120 feet long. Others were the size of a chicken and weighed as little as 8 pounds. All non-avian dinosaurs lived on land. Some may have gone into the swamps and lakes for food, but they did not live entirely in water. Meat-eaters walked on two legs and hunted alone or in groups. Plant-eaters walked on either two or four legs and grazed on plants.
The feature that distinguishes dinosaurs from other reptiles is a hole in the hip socket, which allowed dinosaurs to walk upright. Pterosaurs, or flying reptiles, and plesiosaurs, ocean-dwelling reptiles, did not have this feature and were not dinosaurs.
This selection of dinosaurs has been arranged by the geologic time period in which each animal lived.
Triassic (251–201 million years ago)
Coelophysis, was a light, agile, 8 to 10-foot-long dinosaur.
Jurassic (201-145 million years ago)
Although not nearly as large as its leviathan later relatives, such as Apatosaurus and Barosaurus, Plateosaurus, with a body measuring about 25 feet long, was quite large for an early member of the dinosaurian lineage.
An intimidating carnivore, Allosaurus reigned as one of the Late Jurassic's top predators.
Apatosaurus, which means “deceptive lizard,” is now the valid scientific name for the same dinosaur that used to be called Brontosaurus, a much more appealing and descriptively appropriate name, meaning “thunder lizard.”
Barosuaurus was an extremely long-necked, plant-eating member of the group of dinosaurs called sauropods, which usually stood on their four, sturdy, column-shaped legs.
Another of the long-necked, four-legged sauropods, Camarasaurus was not nearly as large as its cousins Apatosaurus, Barosaurus, Brachiosaurus, and Diplodocus.
Camptosaurus is a relatively small and rare example of the Late Jurassic, North American dinosaurs.
In Diplodocus, the slender neck and whip-like tail are extremely long, and the skull is slender and low, almost streamlined, even though the snout is broad and blunt.
With an adult length of 60 feet and a height of 11 feet at the shoulder, Mamenchisaurus is a moderately sized sauropod dinosaur.
Although the Late Jurassic is best known for its dinosaurian behemoths, such as Apatosaurus, Stegosaurus and Allosaurus, smaller forms scurried underfoot, including the pint-sized Ornitholestes.
Long-recognized as one of the most bizarre animals of all time, Stegosaurus more than earns that reputation with its dazzling assortment of dense, bony plates, and spikes arranged along its backbone.
Cretaceous (145–66 million years ago)
A powerful and intimidating carnivore in its own right, Albertosaurus is a close, slightly smaller cousin of Tyrannosaurus.
Despite its impressive size from a human perspective, as illustrated by the paired mounts at the Museum, Anatotitan was a medium-sized hadrosaur, or duckbilled dinosaur.
Somewhat reminiscent of mammalian armadillos and their relatives the glyptodonts, Ankylosaurus was one of the armored reptilian tanks of the Cretaceous.
This massive, four-legged sauropod dinosaur was undoubtedly one of the largest animals ever to walk on Earth.
With a body reaching about 20 feet in length, Centrosaurus, which belongs to a group of horned dinosaurs called centrosaurines, was smaller than its more famous cousin Triceratops, which belonged to the other major group of horned dinosaurs called chasmosaurines.
Chasmosaurus kaiseni /belli
Only 17 feet long as an adult, Chasmosaurus is the smallest of the advanced horned dinosaurs called chasmosaurines.
With a skeleton about 25 feet long, Corythosaurus is a flashy member of the group of duck-billed dinosaurs called hadrosaurs, which habitually walked and ran on their two hind legs.
Deinonychus was a relatively small, but nonetheless, voracious meat-eater, about 7 feet long, which belonged to a group of theropod dinosaurs called maniraptors, which means “hand-robber.”
A member of the tank-like ankylosaurs, Edmontonia was a heavily armored, highly spiked herbivore, whose body armor was probably its greatest defense against predators.
Although the skull of the 30-foot-long Edmontosaurus is not elaborately crested as in some its evolutionary cousins, such as Corythosaurus, it still exhibits the duck-shaped bill and complex tooth arrangement found in all duckbills, or hadrosaurs.
Standing between 4 and 5 feet in height, Hesperornis is fairly large in comparison to most modern birds, but its size is not the characteristic that stood out to the early fossil hunters and paleontologists who saw its skeleton.
Like other duckbills, which are more formally called hadrosaurs, Hypacrosaurus grew to a length of about 30 feet and habitually moved around on all four limbs, even though its hind limbs were far longer and more developed than its front ones.
Adorned with a bizarre, double-pronged crest atop its skull, Lambeosaurus belongs to the group of duckbilled dinosaurs or hadrosaurs called, not surprisingly, lambeosaurines.
This diminutive dinosaur skeleton indicates that this individual would have only been about 4 feet long. Mononykus olecranus Mononykus was a very weird animal. Only about the size of a turkey, its proportionally long, slender, hind legs powered its fairly slim, streamlined body.
Although small at only 5-6 feet long, Oviraptor is, nonetheless, one of the most bizarre dinosaurs ever discovered, and as such, has long both befuddled and intrigued paleontologists.
Among the most unusual of all dinosaurs, Pachycephalosaurus, whose name basically means “thick-headed lizard,” is best known for the dome of bone that sits atop its skull, which is surrounded by small bony knobs and small bony horns on the snout.
Although a member of the duckbilled dinosaur clan, Prosaurolophus is not one of the more remarkable representatives of this often elaborately crested group. Protoceratops andrewsi The sturdy, pig-sized skeleton of Protoceratops is crowned with an ornate skull adorned with a more extensively, if not yet completely, developed shield of bone at the back than in its earlier evolutionary cousin, Psittacosaurus.
Psittacosaurus is a 3-foot-long, early representative belonging to the group of horned dinosaurs called ceratopsians.
Saurolophus belonged to the group of dinosaurs called hadrosaurs, which are also informally called duckbills.
The sturdy, tank-like dinosaur Sauropelta belongs to a primitive group of ankylosaurs called nodosaurs.
Saurornithoides was another relatively small, agile, meat-eating dinosaur about the same size as Velociraptor and Oviraptor, with which it roamed the sandy desert dune fields of ancient Central Asia.
Struthiomimus quite appropriately means “ostrich-mimic.” This 15-foot-long dinosaur, with its small skull perched atop a long S-shaped neck, does indeed resemble its living dinosaurian cousin, the ostrich.
A close evolutionary cousin of the famous horned dinosaur Triceratops, Stryracosaurus possessed a similarly husky and brutish body, with four stout legs supporting a barrel-chested torso somewhat similar to that of a modern rhino.
Tenontosaurus is a very close relative of the more famous dinosaur from Europe called Iguanodon.
With its stocky and husky 25-foot-long skeleton, Triceratops would have been a formidable adversary even without its massive and bizarre skull, armed with three intimidating horns and a sturdy shield of bone at the back.
Probably the most famous of all extinct dinosaurs, the mighty Tyrannosaurus possessed a surprisingly light, hollow-boned, 40-foot-long skeleton.
The lithe, 6-foot-long skeleton of Velociraptor made this predator one of the most swift and agile carnivores roaming the sand dune fields of the ancient Gobi Desert.
Cenozoic (66 million years ago to present day)
Although Diatryma is clearly a bird, it certainly doesn't look like a typical modern bird.
In life, Presbyornis stood about 18 inches tall. Its stork-like, stilted legs reflect its shorebird habits.
About 2.5-3 feet tall, Psilopterus belongs to a group of predominantly South American ground-dwelling birds called phorusrhacids.