ZoomDinosaurs.com Dinosaur and Paleontology Dictionary

SKELETON A skeleton is the supporting structure of an animal's body. Dinosaur skeltons were made of bones and cartilage.

SKULL The skull is the bony structure of the head that encloses the brain and supports the jaws.

SKULL CREST Some dinosaurs had skull crests, bony protrusions on their skull. Some dinosaurs with skull crests include: Parasaurolophus (pictured above), Dilophosaurus, Corythosaurus, Lambeosaurus, Saurolophus, and many more. Skull crests may have been used for display or for making sounds.

SMILODON (pronounced SMILE-oh-don) Smilodon (meaning "knife tooth"), the largest saber-toothed cat (or saber-toothed tiger), was a fierce predator about 4-5 feet (1.2-1.5 m) long. Its one foot (30 cm) long skull had 2 huge canine teeth (they were serrated and oval in cross-section) in powerful jaws that opened to an angle of about 120°. It also had very strong jaw and neck muscles that let smilodon stab prey with its deadly teeth. It had a short, bobbed tail. It may have eaten thick-skinned prey like mastodons (hairy, extinct elephants) and bison. Thousands of fossils have been found in late Pleistocene tar pits and rocks from both North America (S. californicus in California) and South America (S. neogaeus in Argentina). Classification: family Nimravidae (early cats). Smilodon was named by Plieninger in 1846.

SONORASAURUS (pronounced son-OR-ah-SAWR-us) Sonorasaurus (meaning "Sonora lizard") was a large, plant-eating dinosaur, a brachiosaurid sauropod from the middle Cretaceous period, roughly 99-112 million years ago. This giant was about 45-55 feet (14-17 m) long. This dinosaur had a giraffe-like stance, a long-neck, a long-tail, a bulky body, and a small head. It was about 1/3 the size of Brachiosaurus. An incomplete fossil was found in 1995 by geology student Richard Thompson in southern Arizona, USA (in the Sonora Desert, hence its name). An Acrocanthosaurus tooth was also found at the site, indicating that it may have eaten Sonorasaurus. The type species is S. thompsoni. Sonorasaurus was named by Ratkevich in 1998.

SORDES (pronounced SOR-dees) Sordes (meaning "demon") was a pterosaur with a 1.5 feet (0.5 m) wide wingspan with a thick, hairy coat on the body (but not on the tail or wings), a long, pointed tail, and no head crest. From Kazakhstan, Asia, during the late Jurassic period. It was not a dinosaur, but a type of extinct, flying reptile. It was named by Sharov in 1971.

SP. Sp. is an abbreviation for "species." Sp. is often used when the genus is known, but the species is not. For example, Tyrannosaurus sp. means a Tyrannosaurus fossil of an undetermined species; it is not known whether it is T. rex, T. bataar, T. efremovi, or a new Tyrannosaurus species.

SPECIATION Speciation is the process in which a single species differentiates into two distinct species. One method by which this occurs is geographic isolation, in which two subpopulations of a single species are separated and no longer interbreed. Since the pressures of natural selection differ for the two groups, the two populations become more and more different from one other.

SPEED Paleontologists can deduce approximate dinosaur speeds by using fossilized trackway and the dinosaur's skeletal structure. In 1976, the British zoologist R. McNeill Alexander used elephants, birds, people, and many other living animals to formulate an equation relating an animal's speed, leg length, and its stride length. Solving for speed, the equation is: Speed (m/sec)=0.25*(stride length)1.67*(leg length)-1.17*(gravitational constant)0.5 The gravitational constant is 9.8 m/sec2. Leg length is estimated using Alexander's equations relating hip height to the length of the part of the foot that hits the ground. This is necessary because it is very difficult to determine which dinosaur made a set of tracks. (ref: Alexander, R.M., 1976, Estimates of speeds of dinosaurs, Nature 261: 129-130).

SPHENODOCOELUS Sphenocoelus was a large, thick-skinned, small-brained, rhinoceros-like mammal. It was an early brontothere.

SPHENODONTIAN Sphenodontians (also called Tuataras) are lepidosaurian reptiles (lizards) that peaked during the Triassic period, about 220 million years ago. Only two species are still alive, Sphenodon punctatus and S. guntheri. Classification: Diapsida, Lepidosauria, Rhynchocephalia.

SPHENOPSIDS Sphenopsids (horsetails) are primitive, spore-bearing plant with rhizomes. These fast-growing, resilient plants were common during the Mesozoic Era. The side branches are arranged in rings along the hollow stem. Horsetails date from the Devonian period 408-360 million years ago, but are still around today and are invasive weeds. Huge horsetails went extinct in the Permian mass extinction; smaller ones lived during the Mesozoic Era.

SPINOSAURID (pronounced SPINE-oh-SAWR-ids) Spinosaurids were a large, theropod from the Cretaceous period. These meat-eating dinosaurs had three-fingered hands and vertebral spines. Other Spinosaurids include Angaturama, Baryonyx, Irritator, Suchomimus, Siamosaurus and Spinosaurus.

SPINOSAURUS (pronounced SPINE-oh-SAWR-us) Spinosaurus was a large, sail-backed, spinosaur, a theropod from the late Cretaceous period, 97.5 million-95 million years ago. This meat-eating, bipedal dinosaur was named by Stromer in 1915. The type species is S. aegypticus.

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