Ankylosaurus: These dinosaurs grew up to 33 feet (10 meters) long. They had a wide head, with triangular horns and bony plates covering their bodies, and for defense they used their stiffened, club-shaped tail. Most Ankylosaurus fossils are found in North America.

Tenontosaurus: This ornithopod’s fossils are found mostly in western North America. It appears to have been a transitional form to the more advanced iguanodontids—a primitive iguanodont. It measured up to 22 to 27 feet (6.5 to 8 meters) long, had a very long, stiffened tail, and probably walked on all four feet. Iguanodon: Another ornithopod dinosaur, the Iguanodon roamed Europe and North America. It was also the first dinosaur fossil ever found. The Iguanodon measured up to about 33 feet (10 meters) long, probably chiefly moved on all fours, and had a conical thumb spike on the first digit of its hand.

Shantungosaurus: Fossils of this largest known hadrosaur were found in China. It measured approximately 50 feet (15 meters) long—as big as many sauropods—and had a skull about 5.35 feet (1.63 meters) long. Its beak was toothless, but its jaws were packed with around 1,500 tiny chewing teeth.

Parasaurolophus: This dinosaur’s head crest is the shape of an elongated tube that extends backward behind the skull; many fossils are from North America.

Orodromeus: This North American dinosaur was found in Montana. It grew up to six feet (two meters) in length.

Hypsilophodon: The “high-ridged tooth” dinosaur may have been one of the fastest running ornithischian dinosaurs. It also had a horny beak to cut vegetation and its teeth could easily grind plants.

Heterodontosaurus: This “different toothed lizard” averaged about 3 feet (1 meter) in length; some scientists believe it may have burrowed under the ground during the summer.

Pachycephalosaurus This dinosaur’s thickened skull was ornamented with bony knobs, and is thought to have been used in head butting. Most fossils come from North America.

Stegoceras: This dinosaur was about 6 feet (2 meters) long, with the females and males exhibiting different thicknesses in skulls.

Psittacosaurus: Found in Mongolia, scientists believe this “parrot lizard” was a primitive ceratopsian. It’s actually called a psittacosaurid ceratopsian dinosaur. In fact, it is one of the most completely known dinosaur genera, with over 400 individual fossils collected so far. The dinosaur was bipedal, with a very rudimentary frill, and is therefore often considered to be frill-less.

Protoceratops: This Mongolian dinosaur was quadrupedal, with a prominent, but short frill. It is therefore often considered to be frill-less. It also lacked the horns seen in later ceratopsian dinosaurs.

Triceratops: The Triceratops is another well-known dinosaur from North America. It had a nose horn and paired horns over the eyes. It grew up to 26 feet (8 meters) long, with a short and solid frill; it was one of the last species of dinosaur to roam Earth.

The Parasaurolophus sported a weird head crest. Paleontologists are not sure what it was used for, but one possible explanation is that it helped the animal’s vocalizations to have increased volume and resonance (Big Stock Photo).

Torosaurus: This North American dinosaur had a longer frill than Triceratops. Its six-foot (two-meter) skull is one of the longest known of any land animal.