Saurophaganax ("Lizard-eating master") is a genus of allosaurid dinosaur from the Morrison Formation of Jurassic North America. Some paleontologists consider it to be a species of Allosaurus (A. maximus). Saurophaganax is very large (10.9 meters (36 ft) long) and in fact it may have been the largest carnivore of Late Jurassic North America.

Saurornithoides is a genus of troodontid maniraptoran dinosaur, living during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. Saurornithoides, like others in its family, was probably predominantly carnivorous. Estimates of its length range from 2 to 3 metres (6.6 to 9.8 ft) and weight from 23 to 54 kilograms (51 to 120 lb). It had large eye sockets and stereoscopic vision, allowing for good depth perception. It probably had good vision in light and very good night vision. It had a long, low head, a depressed muzzle, sharp teeth and a relatively large brain. Swift and smart, like its North American cousin Troodon, Saurornithoides probably scoured the Gobi Desert, looking for small mammals or reptiles to eat. Scientists speculate that it used its long 'arms' and grasping 'hands' to seize live prey, which would have consisted of small animals. Like other troodontids, it had an especially large claw on the second toe of each foot.

Saurornitholestes ("lizard-bird thief") is a genus of coyote-sized carnivorous dromaeosaurid dinosaur from the Upper Cretaceous (Upper Campanian stage) of Alberta, Canada. Several partial skeletons, dozens of isolated bones, and scores of teeth are known from the badlands of Dinosaur Provincial Park in Alberta; most of these are housed at the Royal Tyrrell Museum of Palaeontology, in Drumheller, Alberta. Like other theropods in the family Dromaeosauridae, Saurornitholestes had a long, curving, blade-like claw on the second toe. Saurornitholestes was more long-legged and lightly built than other dromaeosaurids such as Velociraptor and Dromaeosaurus. It resembles Velociraptor in having large, fanglike teeth in the front of the jaws. Saurornitholestes most closely resembles Velociraptor, although the precise relationships of the Dromaeosauridae are still relatively poorly understood. Saurornitholestes appears to have been the most common small theropod in Dinosaur Provincial Park, and teeth and bones are much more common than those of its more massive contemporary, Dromaeosaurus. Little is known about what it ate and how it lived, but a tooth of Saurornitholestes has been found embedded in the wing bone of a large pterosaur, probably a juvenile Quetzalcoatlus. Because the pterosaur was so much larger than Saurornitholestes, Currie and Jacobsen suggest that the theropod was probably scavenging the remains of an already dead animal.

Segnosaurus ("Slow lizard") is a genus of theropod dinosaur belonging to the family Therizinosauridae.

Sinornithoides ("Chinese Bird Form") is a genus of troodontid theropod dinosaur. It lived during the Early Cretaceous (Aptian to Albian stages, around 120 to 100 million years ago). It is one of the smallest known theropods, approximately 1 meter long (3 ft). It lived in China, and probably ate invertebrates and other small prey.

Sinornithosaurus ("Chinese bird-lizard") is a genus of feathered dromaeosaurid dinosaur from the Lower Cretaceous Period (Middle Barremian) of the Yixian Formation in what is now China. Sinornithosaurus was a member of the family Dromaeosauridae, a group of agile, predatory dinosaurs with a distinctive sickle-shaped toe claw, which also includes Deinonychus and Utahraptor. It lived about 125 million years ago in the Barremian age of the Lower Cretaceous period, which makes it among the earliest and most primitive dromaeosaurids yet discovered. The presence of vaned feathers on Sinornithosaurus is consistent with feather evidence from other dromaeosaurs. see Microraptor, Velociraptor, and Rahonavis.

Sinosauropteryx ("Chinese lizard-wing") is the first and most primitive genus of dinosaur found with the fossilized impressions of feathers. It lived in China during the early Cretaceous period and may have been a close relative of Compsognathus. It was the first dinosaur genus discovered in the famous Liaoning Province. The largest known specimens are 1-1.20 meters (3 ft) in length, most of which was taken up by its extremely long tail. The remarkably well-preserved fossils show that Sinosauropteryx was covered with a furry down of very simple feathers - though some contention arose with an alternative interpretation of the filamentous impression as collagen fiber remains. These filaments consisted of a simple two-branched structure, roughly similar to the secondarily primitive feathers of the modern kiwi.

Sinraptor is a genus of theropod dinosaur from the Late Jurassic. The name Sinraptor comes from the Latin prefix "Sino", meaning Chinese, and "Raptor" meaning thief. The specific name dongi honours Dong Zhiming. Despite its name, Sinraptor is not related to dromaeosaurids (often nicknamed "raptors") like Velociraptor. Standing nearly 3 meters tall (10 ft) and measuring roughly 7.6 meters (25 ft) in length, two species of Sinraptor have been named. S. dongi, the type species, was described by Currie and Zhao in 1994. A second species, originally named Yangchuanosaurus hepingensis by Gao in 1992, may actually represent a second species of Sinraptor. Whether or not this is the case, Sinraptor and Yangchuanosaurus were close relatives, and are classified together in the family Sinraptoridae.

Spinosaurus ("Spine lizard") is a genus of theropod dinosaur which lived in what is now North Africa, from the Albian to early Cenomanian stages of the Cretaceous period, about 100 to 97 million years ago. The distinctive spines of Spinosaurus, which were long extensions of the vertebrae, grew up to 2 meters (7 ft) long and were likely to have had skin connecting them, forming a sail-like structure, although some authors have suggested that they were covered in muscle and formed a hump or ridge. Multiple functions have been put forward for this structure, including thermoregulation and display. According to recent estimates, Spinosaurus is the largest of all known carnivorous dinosaurs, even larger than Tyrannosaurus rex and Giganotosaurus. These estimates suggest that it was around 16 to 18 metres (52 to 59 ft) in length and 7 to 9 tonnes (7.7 to 9.9 short tons) in weight.

Staurikosaurus ("Lizard of the Southern Cross") is a genus of early dinosaur from the Late Triassic of Brazil. Staurikosaurus is one of the earliest dinosaurs that is known. At just 2 metres in length (6.5 ft),[1] 80 centimetres tall (31 in), and weighing just 30 kilograms (66 lb), Staurikosaurus was tiny in comparison to later theropods like Megalosaurus. Newer research seems to confirm that Staurikosaurus and the related Eoraptor and Herrerasaurus are definite theropods and evolved after the sauropod line had split from the Theropoda.

Struthiomimus ("Ostrich mimic") is a genus of ornithomimid dinosaur from the late Cretaceous of Alberta, Canada. It was a long-legged, ostrich-like dinosaur. Struthiomimus had a typical build and skeletal structure for an ornithomimid, differing from genera like Ornithomimus and Dromiceiomimus in proportions and anatomical details. It is known from several skeletons and skulls,and its size is estimated as about 4.3 metres (14 ft) long and 1.4 metres (4.6 ft) tall at the hips, with a weight of around 150 kilograms (330 lb). As with other ornithomimids, it had a small slender head on a long neck (which made up about 40% of the length of the body in front of the hips). Its eyes were large and its jaws were toothless. Its vertebral column had ten neck vertebrae, sixteen back vertebrae, six hip vertebrae, and an unknown number of tail vertebrae. The tail was stiff and was probably used for balance.

Struthiomimus had long slender arms and hands, with immobile forearm bones but limited opposability between the first finger and the other two. It had the longest hands of any ornithomimid, with particularly long claws. The three fingers were roughly the same length, and the claws were only slightly curved. Its shin was longer than its thigh, a cursorial feature. Among ornithomimids, though, its legs were only moderately elongate. Its feet were elongate, and the metatarsals were tightly appressed, with three toes tipped by claws with very slight curvature.

Suchomimus ("Crocodile mimic") is a genus of large spinosaurid dinosaur with a crocodile-like mouth that lived 110 to 120 million years ago, during the middle portion of the Cretaceous period in Africa. Unlike most giant theropods, Suchomimus had a very long, low snout and narrow jaws studded with some 100 teeth, not very sharp and curving slightly backward. The tip of the snout was enlarged and carried a "rosette" of longer teeth. The animal is reminiscent of crocodilians that eat mainly fish, such as the living gharial, a type of large crocodile with a very long, slim snout, from the region of India. Detailed study shows that the specimen of Suchomimus was a subadult about 11 meters (36 ft) in length, but scientists think that it may have grown to about 12 meters (40 ft) long, approaching the size of Tyrannosaurus. The overall impression is of a massive and powerful creature that ate fish and presumably other sorts of meat (carrion, if naught else) more than 100 million years ago, when the Sahara was a lush, swampy habitat.

Szechuanosaurus ("Szechuan lizard") is a genus of sinraptorid dinosaur from the Late Jurassic. This dinosaur lived in the Asia in the Oxfordian and Tithonian. It resembled a small Allosaurus, with a weight of 100 - 150 kilograms (220 - 330 lb) and a length of 8 meters (27 ft).

Tarbosaurus ("Terrifying lizard") is a genus of tyrannosaurid theropod dinosaur that flourished in Asia between 70 and 65 million years ago, near the end of the Late Cretaceous Period. Fossils have been recovered in Mongolia with more fragmentary remains found further afield in parts of China. Although many species have been named, modern paleontologists recognize only one, T. bataar, as valid. Some experts contend that this species is actually an Asian representative of the North American genus Tyrannosaurus. Tarbosaurus lived in a humid floodplain criss-crossed by river channels. In this environment, it was an apex predator at the top of the food chain, probably preying on other large dinosaurs like the hadrosaur Saurolophus or the sauropod Nemegtosaurus.

Therizinosaurus ("Scythe lizard") is a genus of very large theropod dinosaur. Known from very incomplete remains, it is estimated to have grown up to 9.6 meters (32 ft) long and reach 3-6 tonnes (3-7 short tons) in weight. Therizinosaurus lived in the late Cretaceous Period (late Campanian-early Maastrichtian stages, around 70 million years ago), and was one of the last and largest representatives of its unique group, the Therizinosauria. Its fossils were first discovered in Mongolia and they were originally thought to belong to a turtle-like reptile (hence the species name, T. cheloniformis — "turtle-formed").

Torvosaurus ("Savage lizard") is a genus of large theropod dinosaur that lived during the Tithonian stage of the Late Jurassic period. Fossilized remains of Torvosaurus have been found in North America and Portugal. Torvosaurus reached 9 to 11 meters (30 to 36 ft) in length and an estimated weight of about 2 metric tons (2.2 tons), which made it the largest carnivore of its time, except for possibly Epanterias (perhaps just a big Allosaurus) and Saurophaganax.

Troodon is a genus of relatively small, bird-like dinosaur from the Late Cretaceous period (75-65 mya). Discovered in 1855, it was among the first dinosaurs found in North America. Troodon was a small dinosaur, around 2 metres (6.6 ft) in length, 1 metre (3.3 ft) tall, and weighed about 27 to 45 kilograms (60 to 99 lb). It had very long, slender limbs, suggesting that the animal was able to move quickly. It had long 'arms' that folded against the wall of the thorax like a bird's. It had large, retractable sickle-shaped claws on its second toes, which were raised off the ground when running. Troodon had one of the largest known brains of any dinosaur, relative to its body mass (comparable to modern birds). Hence it is believed to have been one of the most intelligent dinosaurs, even more intelligent than mammals of that era.

Tyrannosaurus ("Tyrant lizard") is a genus of theropod dinosaur. The famous species Tyrannosaurus rex, commonly abbreviated to T. rex, is a fixture in popular culture around the world. It lived throughout what is now western North America, with a much wider range than other tyrannosaurids. Fossils of T. rex are found in a variety of rock formations dating to the last three million years of the Cretaceous Period, approximately 68 to 65 million years ago; it was among the last non-avian dinosaurs to exist prior to the Cretaceous–Tertiary extinction event. Like other tyrannosaurids, Tyrannosaurus was a bipedal carnivore with a massive skull balanced by a long, heavy tail. Relative to the large and powerful hindlimbs, Tyrannosaurus forelimbs were small, though unusually powerful for their size, and bore two clawed digits. Although other theropods rivaled or exceeded T. rex in size, it was the largest known tyrannosaurid and one of the largest known land predators, measuring up to 13 metres (43 ft) in length, up to 4 metres (13 ft) tall at the hips, and up to 6.8 metric tons (7.5 short tons) in weight. By far the largest carnivore in its environment, T. rex may have been an apex predator, preying upon hadrosaurs and ceratopsians, although some experts have suggested it was primarily a scavenger.

Utahraptor ("Utah's predator") is the largest known member of the theropod dinosaur family Dromaeosauridae, and dates from the Early Cretaceous period (132-119 million years ago). Like other dromaeosaurids, Utahraptor had a huge curved claw on the second toe, one is preserved at 22 centimetres (8.7 in) in length and is thought to reach 24 centimetres (9.4 in) restored. Up to 6.5 m (21 ft) long, 2 m (6.6 ft) tall, and 700 kg (1,500 lb) in weight, Utahraptor would have been a formidable predator. It is thought that Utahraptor may be closely related to the much smaller Dromaeosaurus and the giant Mongolian dromaeosaurid Achillobator.

Velociraptor ("Swift seizer") is a genus of dromaeosaurid theropod dinosaur that existed approximately 75 to 71 mya (million years ago) during the later part of the Cretaceous Period. Smaller than other dromaeosaurids like Deinonychus and Achillobator, the turkey-sized Velociraptor nevertheless shared many of the same anatomical features. It was a bipedal, feathered carnivore with a long, stiffened tail and an enlarged sickle-shaped claw on each hindfoot, which is thought to have been used to kill its prey. Velociraptor can be distinguished from other dromaeosaurids by its long and low skull, with an upturned snout.

Yangchuanosaurus was a theropod dinosaur that lived in China during the Late Jurassic period, and was similar in size and appearance to its North American contemporary, Allosaurus. It hails from the Upper Shaximiao Formation and was the largest predator in a landscape which included the sauropods Mamenchisaurus and Omeisaurus as well as the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. Yangchuanosaurus was a fairly large theropod. The type specimen of Y. shangyouensis had a skull 82 cm (2.7 ft) long, and its total body length was estimated at about 8 m (26 ft). Another specimen, assigned to the new species Y. magnus, was even larger, with a skull length of 1.11 m (3.6 ft). It may have been up to 10.8 m (35.4 ft) long, and weighed as much as 3.4 metric tons (3.7 short tons). There was a bony knob on its nose and multiple hornlets and ridges, similar to Ceratosaurus. It had a massive tail that was about half its length.