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These extinct cats are notable for two huge canine teeth plus other sharp teeth in powerful jaws. These mammals also had very strong jaw and neck muscles that let them stab prey with their deadly teeth. They ate mammoth, rhinoceros, and other thick-skinned animals. Examples include: Smilodon (the largest and most powerful, from N. America), Hoplophoneus (with short teeth, from the Oligocene), Eusmilus (leopard-sized with very long teeth, from the Oligocene), and Machairodus (lion-sized and common; from Europe during the Paleocene). Fossils have been found in Pliocene to early Pleistocene rocks from both North and South America and other Northern continents.

Sacral vertebrae (also called sacral ribs) are the part of the backbone that is attached (fused) to the pelvis in dinosaurs.

The sacrum is the part of the backbone that is attached to the pelvis.

(pronounced siy-KAHN-ee-ah) Saichania (meaning: "beautiful" in Mongolian) was a heavily-armored, plant-eating dinosaur that lived during the late Cretaceous Period, about 79-75 million years ago. It was an ankylosaurid, a plated, slow-moving, quadrupedal ornithischian with a clubbed-tail and bony spikes and knobs running along its sides. It had a wide, boxy head with unusual nasal bones that may have cooled and moistened inhaled air; it may have had an acute sense of smell. Both body armor and stomach armor have been found for Saichania (other ankylosaurs may have had belly armor, but it has not been found for them). Saichania was about 23 ft (7 m) long. Three fossils were found in Mongolia. The type species is S. chulsanensis. Saichania was named by paleontologist Maryánska in 1977.

A group of amphibians that evolved in the Middle Jurassic period. There are about 400 living species most commonly occurring in fresh water and damp woodlands where they feed on snails, worms insects and other small animal.

Salienta (or Anura, meaning: "no tail," since these amphibians lose their tail as an adult) is the group of frogs, toads, and their close fossil relatives. The earliest anuran is Triadobatrachus, from the early Triassic Period.

(pronounced SALT-ah-SAWR-us) Saltasaurus (meaning: "Salta lizard," Salta is a province of NW Argentina) was a long-necked plant-eating dinosaur about 40 feet (12 m) long. It lived during the late Cretaceous Period, roughly 83 million to 79 million years ago. It was a titanosaurid, a plated sauropod from what is now Argentina and Uruguay in South America. The plates on its back may have had spikes on them for protection. This quadruped is known from the following fossils: a few oval and circular armored plates (3.8-4.5 inches = 10-12 mm in diameter), hundreds of bumps which covered its back (1/4 inch = 6-7 mm in diameter), and several incomplete skeletons, including some vertebrae, limb bones, and jaws. Saltasaurus was named by paleontologists J. Bonaparte and J. Powell in 1980. The type species is S. loricatus.

(pronounced SALT-oh-po-SOOK-us) Saltoposuchus (meaning: "leaping crocodile") was a lightly-built, bipedal reptile (a primitive Crocodylomorph, not a dinosaur) that was 3 ft 9 inches (1.15 m) long. This meat-eater had sharp, pointed teeth and two rows of armored plates on its back. It had long back legs, short front legs, and a long tail. Saltoposuchus lived during the late Triassic Period, roughly 210 million years ago. Fossils were found in Europe and North America.

(pronounced SALT-oh-pus) Saltopus (meaning: "leaping foot") was an early, small, meat-eating dinosaur from the late Triassic Period, about 225 million to 222 million years ago. Its fossil was found in Scotland. The type species is S. elginsis.

Saltriosaurus (meaning: Saltrio [a town in Italy] lizard) is an unpublished and informal name for a meat-eating dinosaur found in a quarry near Saltrio, in northern Italy. This theropod dinosaur lived during the early Jurassic Period, roughly 200 million years ago. Saltriosaurus was a biped about 26 feet (8 m) long and13 feet (4 m) tall). The skull was 28 inches (70 cm) long and the single tooth that was found was about 2.8 inches (7 cm ) long. About 10 percent of this fossil has been found; Angelo Zanella discovered this fossil in 1996. Saltriosaurus is the oldest-known three-fingered dinosaur. This dinosaur resembled Allosaurus. Saltriosaurus was named by Dal Sasso (it is a nomen nudem).

A compacted sedimentary rock consisting primarily of sand-sized grains of quartz.

(pronounced SAHN-ba-SAWR-us) Sanpasaurus (meaning: "Sanba [ancient name for Sichuan, China] lizard") was a huge plant-eating dinosaur that lived during the middle Jurassic Period, about 150-145 million years ago. It had long front legs and was a hadrosaur, a duck-billed dinosaur from what is now China. Some bones that were found with it are probably from a sauropod. Sanpasaurus was named by Young in 1946. The type species is S. yaoi. Its classification is unsure and it is a dubious genus.

(pronounced san-TAN-a-RAP-tor) Santanaraptor (meaning: "Santana [a rock formation in northeastern Brazil] plunderer") was a fast-running, meat-eating dinosaur that lived during the middle Cretaceous Period, roughly 112 to 99 million years ago. A partial skeleton and some skin impressions of this coelurosaurid theropod were found in Brazil. It was about 6.5 feet (2 m) tall, weighing roughly 65 pounds (30 kg). Santanaraptor was named by A. W. A. Kellner in 1999. The type species is S. placidus.

Sarkastodon was a huge, early mammal that lived during the late Eocene, about 35 million years ago. This bear-like carnivore (meat-eater) was about 10 ft (3 m) long. Fossils of this creodont have been found in Central Asia (Mongolia). It was a quadruped (it walked on four feet) with clawed feet, a small brain, a long tail, large jaws and many large teeth. Classification: Class Mammalia (mammals), Infraclass Eutheria (placental mammals), Division Haplorhini, Order Creodonta, Family Oxyaenidae, Genus Sarkastodon.

(pronounced SAHR-co-LESS-teez) Sarcosaurus (meaning: "flesh robber") was a heavily-armored, slow-moving, quadrupedal plant-eating dinosaur roughly 10 feet (3 m) long. This early nodosaur (an early ankylosaur with no tail club) lived during the late Jurassic Period, roughly 161 million to 157 million years ago. It is only known from a fossilized partial lower jaw. Sarcolestes was named by paleontologist Lydekker in 1892. The type species is S. leedsi.

Sarcopterygian fish (Subclass Sarcopterygii) are a type of bony fish with fleshy fins. The fins of these fish are supported by fleshy lobes with bones. Examples include: Coelacanth (pictured above), Australian lungfish, and the extinct Eusthenopteron. These fish gave rise to the amphibians, who led a life in and out of the water. Classification: Class Osteichthyes (bony fish), Subclass Sarcopterygii (fleshy-finned fish).

(pronounced SAHR-co-SAWR-us) Sarcosaurus (meaning: "flesh lizard") was a meat-eating dinosaur perhaps 12 feet (3.5 m) long. It lived during the early Jurassic Period, roughly 206 million to 200 million years ago. It was a theropod from what is now England. This biped is known from only a few bones, including a partial pelvis (hip), a femur (thigh bone), and some vertebrae. It was named by Andrews in 1921. The type species is S. woodi.

(pronounced SAHR-co-SOOK-us) Sarcosuchus (meaning: "flesh crocodile") was a ancient crocodilian (it was not a dinosaur). This giant meat-eater was about 37-40 feet (11-12 m) long and may have weighed up to 10 tons. Its body was covered with bony armor (scutes). There were over 100 teeth in its long jaws and it had an overbite (the top jaw extended beyond the lower jaw). Sarcosuchus lived during the Cretaceous Period, roughly 110 million years ago. Fossils have been found in the Ténéré Desert, Niger, Africa, and the Bahia Basin, Brazil, South America. It was found by French paleontologist Albert-Felix de Lapparent in 1964. The type species is S. imperator (named by France de Broin and Phillipe Taquet in 1966). Paul C. Sereno recently found a large Sarcosuchus in Niger.

(pronounced sawr-IS-key-ans) Saurischian (lizard-hipped) dinosaurs were the ancestors of the birds. They are divided into the theropods (bipedal carnivores) and sauropodomorphs (large, quadrupedal herbivores).

(pronounced sawr-OHL-oh-fuss or SAWR-oh-LOHF-us) Saurolophus (meaning: "crested lizard") was a duckbilled (Hadrosaurinae) dinosaur that had a 5 inch (13 cm) long bony spike extending up from its forehead. Saurolophus was about 30-40 feet (9-12 m) long, had a toothless beak whose top bill curled slightly upwards, had cheek teeth, and could walk on two or four legs. This plant-eater lived during the late Cretaceous period, about 72 million to 68 million years ago. Many fossils have been found in Alberta, Canada and Mongolia. Saurolophus was named by dinosaur hunter B. Brown in 1912. The type species is S. osborni.

(pronounced SAWR-oh-PEL-tah) Sauropelta (meaning: "small-shield lizard") was a large, armored, quadrupedal, herbivore dinosaur from the early Cretaceous period, about 116 million to 91 million years ago. This nodosaurid ankylosaur was named by paleontologist John H. Ostrom in 1970.

(pronounced SAWR-oh-FAG-ah-naks) Saurophaganax (meaning: "king of the lizard eaters") was a large, meat-eating dinosaur (a theropod) from the late Jurassic Period, about 150 million years ago. This huge carnosaur (it may be the same genus as Allosaurus) was perhaps about 45 ft (14 m) long. An incomplete fossil was found in Oklahoma, USA. Saurophaganax was named by Chure in 1995. The type species is S. maximus.

(pronounced sawr-oh-PLIE-teez) Sauroplites (meaning: "lizard armored soldier") was an armored, quadruped, plant-eating dinosaur that dates from the early Cretaceous Period, about 145-97.5 million years ago. This large nodosaurid ankylosaur may have been up to 17 feet (5 m) long (and had no tail club). Fragmentary fossils, including armored plates from the back, have been found in China. Sauroplites was named by Bohlin in 1953. The type species is T. scutiger. Sauroplites is a doubtful genus due to lack of fossil material.

A family of enormous herbivores that co-existed in herds on the plains. Included in this group are Diplodocus, Brachiosaurus, Apatosaurus and Camarasaurus.

(pronounced SAWR-uh-pod-oh-MORF-ah) Sauropodomorphs were a suborder of saurischian (lizard-hipped) dinosaurs. They were quadrupeds with long necks, small heads, and long tails. The earliest-known sauropodomorph is a prosauropod about 230 million years old. Sauropodomorphs include the prosauropods (like Massospondylus) and the sauropods (like Apatosaurus and Diplodocus). Sauropodomorpha was named by von Huene in 1932.

(pronounced SAWR-oh-pa-SYE-din) Sauroposeidon (meaning: "Lizard, God of " was a long-necked plant-eating dinosaur about 60 feet (18 m) long, weighing about 60 tons. It lived during the middle Cretaceous Period, roughly 110 million years ago. It was a brachiosaurid, a sauropod with a giraffe-like stance. Fossils were found in 1994 in Oklahoma. Sauroposeidon was named by Matt Wedel and Richard Cifelli, in 1999, vide Franklin. This genus is a nomen nudum.

Sauropterygia (meaning: "lizard flippers") are an order of extinct aquatic reptiles that includes plesiosaurs, nothosaurs, and perhaps placodonts (their classification is uncertain). Sauropterygians had four flipper-like limbs and a streamlined body; they were well adapted to life in the water. They were not dinosaurs, but were reptiles that also lived during the Mesozoic Era, the time of the dinosaurs. They went extinct at the end of the Creataceous period, about 65 million years ago.

(pronounced SAWR-or-nith-OY-dees) Saurornithoides (meaning: "lizard bird form") was a fast-moving, bipedal, meat-eating dinosaur from the late Cretaceous Period, about 85 million to 77 million years ago. This theropod was about 6.5 to 12.5 ft (2 to 3.5 m) long and weighed about 28-60 pounds (13-27 kg). The type species is S. mongoliensis. It was named by paleontologist Osborn in 1924. Fossils have been found in Mongolia.

(pronounced SAWR-or-NITH-oh-LESS-tees) Saurornitholestes (meaning: "lizard bird robber") was a fast-moving, bipedal, lightly-built, meat-eating dinosaur from the late Cretaceous Period, about 76 million to 73 million years ago. This theropod was very similar to Velociraptor and was about 6 ft (1.8 m) long and weighed about 11 pounds (5 kg). The type species is S. langstoni. Saurornitholestes was named by paleontologist Sues in 1978. Fossils have been found in Alberta, Canada.

Sauros is Greek for lizard.

(pronounced SAWR-oh-SOOK-us) Saurosuchus (meaning: "lizard crocodile") was the biggest rauisuchian (an Archosaur but not a dinosaur) from the late Triassic Period. This huge carnivore (meat-eater) was about 23 ft (7 m) long and had an enormous skull (about 3 ft = 1 m long). It may have weighed 1 to 2 tons. It walked on four short legs, had a long tail, and a short neck; it looked like a huge, big-headed lizard. It probably ate Kannemeyerid Dicynodonts. Saurosuchus was named by Reig in 1959; the type species is Saurosuchus galilei. Fossils have been found in South America.

Saurus (from the Greek word sauros) means lizard.

(pronounced sca-fog-NAYTH-us) Scaphognathus (meaning: "canoe jaw") was a pterosaur with a 3.25 feet (1 m) wide wingspan. It had good eyesight, a poor sense of smell, and a diamond-shaped flap of skin at the end of the long, pointed tail. Scaphognathus was the only long-tailed pterosaur that had a bony head crest. It lived in what is now Europe during the late Jurassic Period. It was not a dinosaur, but a type of extinct, flying reptile, a pterosaur. It was named by Wagner in 1861. The type species as S. crassirostris (meaning: "thick billed"). Two fossil specimens have been found in Germany.

(pronounced sca-FON-iks) Scaphonyx (meaning: "canoe claw") was a rhynchosaur (it was not a dinosaur). This reptile was a quadruped and an herbivore. probably eating seed ferns. It was a land-dwelling, archosauriform reptile. It lived during the late Triassic Period, about 230 million years ago. This short, pig-like reptile had a barrel-shaped body, tusks and a beak. Scaphonyx was named by Woodward in 1908.

(pronounced SKAP-you-lah) The scapula is the shoulder bone. The scapula of Ultrasauros is bigger than a person!

Scavengers are animals that eat dead animals that they did not kill themselves. Most meat-eaters are scavengers. Hyenas are modern-day scavengers.

(pronounced SKEL-eye-doh-SAWR-us) Scelidosaurus (meaning: "limb lizard") was a low-slung, armored, plant-eating dinosaur that was 10-13 feet (3-4 m) long and weighed about 440-550 pounds (200-250 kg). It had a small head,a short neck, leaf-shaped teeth, a long, stiff tail, and a heavy body with armored plates embedded in its back. It may have had a bony beak. These bony plates had pointy studs on them. This quadruped lived during the early Jurassic Period, roughly 206 million to 200 million years ago. It was an Ornithischian dinosaur from what is now England, and Arizona, USA. It is known from two skeletons, one of which was a juvenile. Scelidosaurus was named by paleontologist Owen in 1868. The type species is S. harrisonii.

(pronounced sip-ee-ON-iks) Scipionyx samniticus was a Cretaceous period theropod (from about 113 million years ago), perhaps a maniraptor. It is known from a single, extremely detailed specimen of a hatchling that includes fossilized soft tissues, including muscles and internal organs. It was 9.5 inches (24 cm) long and had a very large head. John A. Ruben, a vertebrate paleobiologist from Oregon State University, used an 80-watt ultraviolet (UV) lamp to help reveal outlines of Scipionyx's fossilized internal organs. Ruben found that the position of Scipionyx's colon (intestines) and liver were similar to that of modern crocodilians (which are cold-blooded), and unlike that of birds (which are warm-blooded). The position of the liver also gives information about the lungs, since a muscle that runs by the liver helps the lungs to expand and contract in crocodilians. Scipionyx probably had reptilian-style lungs (and not highly efficient bird lungs). Although Ruben's work is not absolutely conclusive, it looks like the small theropod Scipionyx may be cold-blooded.

A sclerotic ring (also called sclerotic ossicles) is a ring of bones (found in some animals) that supported the eye. When present, the sclerotic ring is located in the orbit (the eye hole of the skull). Some dinosaurs had sclerotic rings.

(pronounced SKOH-loh-SAWR-us) Scolosaurus is an invalid name for Euoplocephalus, an armored, plant-eating dinosaur from the late Cretaceous Period. It was about 20-23 feet (6-7 m) long.