ZoomDinosaurs.com Dinosaur and Paleontology Dictionary

SEA SCORPIONS Sea scorpions (Eurypterida) are extinct carnivorous marine arthropods (segmented invertebrates with a chitinous exoskeleton and jointed legs). These fierce hunters had a scorpion-like stinger which may have contained poison, 3 pairs of jointed legs, 2 clawed arms, and strong jaws. Some had two paddles for swimming. They may have swum on their backs. Eurypterids include Eurypterus, Onychopterella, Pterygotus, Mixopterus, Slimonia, Palmichnium (an ichnogenus, i.e., known from fossilized trackways), etc. Eurypterids date from the early Paleozoic Era, arising during the Ordovician period, over 400 million years ago. Many are found from the Silurian period. They went extinct in the Permian mass extinction. Eurypterids are the state fossil of New York.

SECERNOSAURUS (pronounced see-SIR-no-SAWR-us) Secernosaurus (meaning "separated lizard") was a small duck-billed dinosaur, a hadrosaur, from the late Cretaceous period, about 73-65 million years ago. It was about 10 ft (3 m) long. It isn't known whether or not it had a crest. The type species is S. koerneri. Fossils (only a few pelvic bones and a partial skull) were found in Argentina, South America. Secernosaurus is the first duck-bill found in South America (most duck-bills and their ancestors, the iguanodonts, have been found in North America). Secernosaurus was named by Brett-Surman in 1979.

SEDIMENT Sediment is any material deposited by wind or water, like rocks and sand.

SEDIMENTARY ROCK Sedimentary rock is rock that has formed from sediment. Most fossils are found in exposed sedimentary rock. In a sequence of sedimentary rocks, the lowest layers are the oldest and the uppermost layers are the youngest (this is the Law of Superposition).

SEED FERNS Seed ferns (Pteridosperms) were primitive seed plants (not ferns at all) that lived in swampy areas from the Mississipian Epoch through the Mesozoic Era. They had woody stems studded with dried out leaf bases. The tops had fern-like fronds which bore seeds. Some seed ferns include Glossopteris (pictured above), Dicroidium, Caytonia, Denkania, and Lidgettonia.

SEELEY, HARRY G. Harry Govier Seeley (1839-1909) was a British paleontologist. In 1887, he divided the dinosaurs by hip structure, into the orders Saurischia and Ornithischia. He named Agrosaurus (1891), Anoplosaurus (1878), Aristosuchus (1887), Craterosaurus (1874), Macrurosaurus (1876), Orthomerus (1883), Priodontognathus (1875), Rhadionsaurus (1881), and Thecospondylus (1882).

SEGISAURUS (pronounced SEG-ee-SAWR-us) Segisaurus (meaning "Segi canyon lizard") was a goose-sized, bipedal, fast-moving, meat- and insect-eating dinosaur from the early Jurassic period, about 206 million to 200 million years ago. Its fossils have been found in Arizona. It was a lightly-built, bird-like theropod dinosaur with a long flexible neck, long head, three-toed feet, a short body, long tail, long, strong legs, arms with long forearms and long, clawed hands. Its collar bone was similar to that of a bird (this characteristic is unusual for dinosaurs and indicated a close link to birds). Segisaurus was named by Charles L. Camp in 1936.

SEGNOSAURUS (pronounced SEG-noh-SAWR-us) Segnosaurus (meaning "slow lizard") was a meat-eating dinosaur perhaps 13 to 30 feet (4-9 m) long (its size is uncertain). It lived during the late Cretaceous period, roughly 97.5 million to 88.5 million years ago. It was a theropod from what is now Mongolia. This biped is known from 3 partial skeletons. It was named by Perle in 1979 . The type species is S. galbinensis.

SEISMOSAURUS (pronounced SIZE-moh-SAWR-us) Seismosaurus (meaning "Earthquake Lizard") was a huge diplodocid dinosaur, up to 170 feet (52 m) long. It may be the longest dinosaur. It lived during the late Jurassic period, about 156 million-145 million years ago. It had a long neck, whip-like tail, and gizzard stones to aid digestion in its stomach. Fossils have been found in New Mexico, USA. The type species is S. halli.

SELLOSAURUS (pronounced SELL-oh-SAWR-us) Sellosaurus (meaning "saddle lizard") was a sauropodomorpha, a primitive plant-eater from the late Triassic period, from 219 -208 million years ago. It was about 21 ft (6.5 m) long. Sellosaurus was named in 1908 by paleontologist von Huene. 21 Partial skeletons, together with gastroliths, were found in Germany. The type species is S. gracilis.

SENONIAN EPOCH (pronounced cen-NOH-nee-an EP-ock) The Senonion epoch was the late (upper) part of the Cretaceous period, about 89 million to 65 million years ago, the end of the Mesozoic Era. The Senonian was named by the French paleontologist Alcide Dessalines d'Orbigny in 1842.

SERENO, PAUL C. Paul C. Sereno (1958 - ) is a US paleontologist from the University of Chicago who has worked in South America, Asia and Africa. He excavated a giant Carcharodontosaurus (1996), found and named Afrovenator (with others, 1994), named the oldest-known dinosaur, Eoraptor (with others, 1993), Suchomimus (1998), Jobaria, and Nigersaurus. Sereno named: Deltadromeus (1996) and Marasuchus (with Arcucci, 1994). He has rearranged the dinosaur family tree, reorganizing the ornithischians and naming the group Cerapoda (1986), formed from the ornithopods and marginocephalians.

SERRATED Serrated means having a jagged edge that is good for sawing. Serrated teeth are good for cutting through meat.

SEXUAL DIMORPHISM Sexual dimorphism is characteristic of having two different forms, one for the males and another for the females of a species. It is very difficult to determine which fossils were male and which were female.

SEYMOURIA (pronounced see-MORE-ee-ah) Seymouria (named after Seymour, Texas, where it was found) was an amphibian from the early Permian period. It was about 2 feet (60 cm) long. It had a strong backbone, four short, sturdy legs, and a short tail, Unlike other amphibians, Seymouria had relatively shorter jaws, ears marked by a notch, and the skull had fewer bones. Its long bones feet and digits were almost like that of a reptile. Seymouria laid its eggs in water. When they hatched, the young changed into their adult shapes (like modern-day frogs change from tadpoles to adults). Fossils have been found in North America.

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