Descriptionary

ceratopsian one of a group of four-legged plant- eaters with beaks and bony head frills. Protoceratops and triceratops were ceratopsians.

Chicxulub a 120-mile (180-km) impact crater in the Yucatan Peninsula believed to be from the aster­oid, meteor, or comet that played a large role in wip­ing out the dinosaurs 65 million years ago. See Alva­rez extinction theory, multiple impact theory, Shiva.

chimera paleontologists' term for a fossil mixture composed of more than one species, named after the mythical monster with a lion's head, goat's body, and snake's tail.

compsognathus during the Jurassic, a theropod that ranged in size from a chicken to a small dog.

Cope's rule a scientific observation that, given adequate food sources, a species will tend to evolve into larger forms over time, which explains the mas­sive growth of the dinosaurs. Although there are a few exceptions, a larger animal tends to be better at winning mates, killing competitors, and fighting off predators.

coprolite literally, "dung stone," fossilized dinosaur feces.

crest a growth or bony plate on top of the head, through which some dinosaurs may have made sounds.

Cretaceous period the time period that encom­passes from 146 to 65 million years ago, at the end of which came the extinction of the dinosaurs.

cycad an evergreen, palmlike tree that served as one of the primary sources of food for herbivores in the Jurassic.

deinocheirus a giant birdlike meat eater with a toothless beak and arms that stretched 8 feet (2.4 m) and is believed to have been able to run as fast as 50 miles per hour (80 km/hr). It lived during the Creta­ceous period.

digitigrade walking on the toes. Predator dinosaurs walked and ran on their toes or the front of their feet for better speed, similar to cats and dogs.

diplodocid a huge, four-legged sauropod with a small head, long neck and tail, and peg teeth. Apa- tosaurus, diplodocus, seismosaurus, and supersaurus were all diplodocids.

disarticulated skeleton paleontologists' term for a fossil skeleton that is found with its bones detached and in various positions and locations.

dromaeosaurid a family of small but fast theropods with retractable, sicklelike claws for slashing prey. The best known were the velociraptors.

duck-billed dinosaur see hadrosaur.

ectothermic cold-blooded, or requiring the Sun or outside warmth to heat one's body to function nor­mally, as with many dinosaurs.

endothermic warm-blooded, or not requiring the Sun's heat to warm one's body to function normally, as a mammal.

extinction the complete dying out of a species, as with the dinosaurs 65 million years ago.

fossil the remains of any living organism from a past geological period. Mineralized bone, teeth, claws, skulls, eggshells, coprolites, and rock-hardened footprints are all fossils.

frill a bony shield protecting the neck and head of a ceratopsian, such as triceratops and protoceratops.

gastrolith a rock purposely swallowed by sauro- pod dinosaurs to help grind food and aid in diges­tion, also believed to be used as ballast by plesio- saurs. Such rocks, rounded and polished from being knocked about, are often found among dinosaur bones.

gigantosaurus a massive meat eater, slightly larger than Tyrannosaurus rex, that lived during the Creta­ceous.

gingko also known as the maidenhair tree, which in the Cretaceous and Jurassic periods served as a pri­mary food source for plant-eating dinosaurs.

grazer any dinosaur that ate grasses and other low- lying plants, such as an ankylosaur or triceratops.

Great Dying, the also known as the Permian- Triassic extinction event, the most massive die-off of marine and land organisms in the history of Earth, occurring in spurts around 251.4 million years ago, which may have played a role in the eventual develop­ment of the dinosaurs. Like the demise of the dino­saurs, the complete wiping out of 70 percent of all land vertebrates and more than 90 percent of marine species may have been due to an asteroid impact.

hadrosaur any one of various types of duck-billed dinosaur, a plant eater that lived during the Creta­ceous period. Unlike the sauropods' dependence on gastroliths to help digest food, the hadrosaurs devel­oped a prodigious number of teeth, possibly the main reason they became so successful.

hallux in predatory dinosaurs, a superfluous claw, also known as a dewclaw, above the side of the foot.

herbivore any dinosaur that ate vegetation instead of meat.

hypacrosaurus a 30-foot (9-m) hadrosaur known for the small fin rising out of its back.

ichnite a non-bone fossil, such as footprints, copro- lites, gastroliths, nests, etc. Also known as ichnofossil.