Alxasaurus: A therizinosaur from Mongolia, the Alxasaurus had longer finger bones than the Therizinosaurus (see below). It is thought to be the most primitive-known member of the therizinosaurs, even though it still had the body shape—long neck, short tail, and long hand claws—of the later therizinosauroids.

Caenagnathus: This oviraptorosaur, meaning “recent jawless,” grew up to 9.5 feet (2.9 meters) in length and lived about 80 million years ago. Like all oviraptorosaurs, it had a toothless jaw that was well-muscled and perfect for crushing; it also probably had feathers.

Carnotaurus: This bizarre dinosaur from Argentina grew up to 30 feet (9 meters) long; it had stumpy arms and a short head with two horns above the eyes.

Daspletosaurus: This genus of tyrannosaurid theropod dinosaur means “frightful lizard.” It is from Canada, and was slightly smaller than the Tyrannosaurus rex, measuring 26 to 30 feet (8 to 9 meters) in length. Its skull was huge, reaching up to 3.3 feet (1 meter) in length.

Deinocheirus: Only a pair of 10-foot-(3-meter-) long forelegs and hands have been found of this dinosaur, which may have been one of the largest of the ornithomimosaurs. Fossils of one animal’s forelegs are on display at the American Museum of Natural History in New York.

Deinonychus: This dinosaur measured up to 11 feet (3.4 meters) long and weighed approximately 161 pounds (73 kilograms), about the size of a mountain lion. These dromaeosaurs had large sickle-shaped claws on the feet, and some fossil evidence indicates that they had a pack-hunting behavior. Most of the fossils of the Deinonychus have been found in North America.

Erlikosaurus: This therizinosaur from Mongolia was long, measuring around 20 feet (6 meters) in length. It also had elongated external nasal openings, slender claws, and a toothless beak.

Gallimimus: This dinosaur (meaning “chicken mimic”) probably ate insects and small animals. It lived in Mongolia about 70 million years ago and is the largest and most completely known of the ornithomimosaurs, measuring around 13 to 20 feet (4 to 6 meters) long.

Nanotyrannus: This dinosaur of the genus tyrannosauid, meaning “dwarf tyrant,” looks like a small version of a Tyrannosaurus. But the fossils are highly debated—are they actually an adult or juvenile tyrannosaurid dinosaur?

Oviraptor: The “egg snatcher or thief” had a bizarre head crest. It was originally thought to prey on others’ eggs, but more recent findings show them brooding eggs in nests, although it is still debated as to whether or not they ate eggs. It also was one of the most bird-like of the non-avian dinosaurs. In particular, its rib cage had several features that are typical of birds, especially something on each rib that would have kept the rib cage rigid.

Saurornithoides: This dinosaur is from a genus of troodontid maniraptoran dinosaur from Mongolia, meaning “bird-like reptile.” The carnivorous dinosaur measured about 6.5 feet (2 meters) long and had a skull with a long, rather bird-like narrow muzzle. The teeth were small, with many teeth in the upper jaw; the teeth’s back edges were serrated. It also had a large brain and large saucer-like eyes, probably for hunting small animals at dusk.

Spinosaurus: This dinosaur was 52 to 59 feet (16 to 18 meters) long, and may have been the largest known carnivorous dinosaur. It had six-foot-(two-meter-) long spines on its back that are thought to have supported a sail; this structure may have played a part in the dinosaur’s thermo-regulation. Most of the fossil remains of this dinosaur have been found in North Africa.

Therizinosaurus: This therizinosaur—possibly herbivorous and maybe one of the last and largest of this unique group—had a relatively short tail and huge forelimbs with enormous sickle-shaped claws. They are thought to be closely related to birds (many illustrations depict the Therizinosaurus with feathers) and may have been one of the largest theropods, measuring 32 feet (9.2 meters) in length.

Troodon: This troodontid, found in North America, had large eyes and possible binocular vision. It was small, at around 6.5 feet (2 meters) in length, and was only about 3 feet (1 meter) tall. Its long, slender limbs indicate that it was fast on its feet.

Tyrannosaurus: One of the largest and most famous of the land-dwelling carnivores, the Tyrannosaurus reached up to 46 feet (14 meters) long and 18.5 feet (5.6 meters) tall. The fossils suggest the females were even larger than the males. One tooth recently took the size prize: it measured 12 inches (30 centimeters) long, including the root when the animal was alive, making it the largest tooth of any carnivorous dinosaur known.

Utahraptor: This dinosaur was up to 21 feet (6.5 meters) long, with a huge, sickle-shaped claw on the second toe that could grow to 9.1 inches (23 centimeters) in length. It is the largest known dromaeosaur found in North America and lived between 132 and 119 million years ago.

Velociraptor: This dinosaur name means “quick plunderer” or “swift seizer”. It was a dromaeosaur about the size of a large dog, almost 6 feet (1.8 meters) long, with a weight of approximately 100 pounds (45 kilograms), and a sickle-shaped slashing claw on each foot. Fossils of this dinosaur are found in Mongolia. The Velociraptor was also prominently featured in the movie Jurassic Park as human-sized terrors; but the actual dinosaur was much smaller and probably had feathers.

A pack of troodons attacks a Euoplocephal, a relative of the ankylosaur. While relatively small, these predators were quick and agile hunters (Big Stock Photo).