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Dinosaurs had many defensive strategies against predators. Ceratopsians used shields, or frills, to protect their necks. Long, sharp horns grew on their brows or snouts. The spike-like thumbs of Iguanodon may have been used as defensive weapons. Ankylosaurs developed a very effective passive method of defense: They were encased in bony plates and spines from head to tail. When threatened, they could have simply flattened on the ground. They were large enough that it would have been difficult for a predator to turn them over and reach their unarmored bellies. In addition, some had mace-like clubs or spikes on the ends of their tails. The tail of a stegosaur was armed with long spikes that would have been useful in discouraging predators. Ornithopods had little in the way of defensive weapons or armor; probably they substituted an excellent sense of smell to warn them of the approach of a predator, then used their speed to escape. Ornithopods may have traveled in herds, which would have given them an advantage in numbers. The sheer size of most sauropods may have been their defense. If an Argentinasaurus were attacked by a carnosaur, it might have simply trampled the predator.

Deinondontidae (Deinodonts)
Translation: Terror Teeth
Deinondontidae (dye-no-DON-tih-day) are important carnosaurs of the Late Cretaceous Period. Some examples of deinodonts are Albertosaurus, Daspletosaurus, and Tyrannosaurus.

Deinonychosauria (Deinonychosaurs)
Translation: Terrible Claw Lizards Deinonychosauria (dyne-ON-ik-o-sawr-ee-ah) is an infraorder of particularly vicious-appearing theropods. These carnivorous dinosaurs walked on their hind legs. One toe of each foot was equipped with a sickle-like claw. In general, they were relatively small and very agile. Included in this infraorder are the families dromaeosauridae, therizinosauridae, and troodontidae. These dinosaurs lived during the Cretaceous Period. A striking example of a deinonychosaur is Deinonychus.

Diapsida (Diapsid)
Translation: Two Arches
Diapsida (dye-APS-ih-dah) is a subclass of Reptilia. Diapsids are marked by double openings behind each eye socket. Diapsida is divided into two groups: snakes and lizards form one group, and the archosaurs (of which dinosaurs are a part) form the other. See also Synapsid

Translation: Forked Lizards
Dicraeosaurinae (dye-CREE-sawr-ih-nay) is a subfamily of Diplodocidae. These dinosaurs had nearly solid vertebrae with few hollow spaces. They are also characterized by their high backs and short necks.

Dinosaur Brain Size
In general, dinosaurs had small brains. Sauropods were the largest of dinosaurs, yet the size of their brains is comparable to that of a modern dog. Given the sauropod's enormous body size, the ratio of brain mass to body mass is the smallest of any of the dinosaurs. The dinosaur with the smallest brain was Stegosaurus. It is difficult to imagine any animal functioning on a brain the size of a golf ball or walnut, yet Stegosaurus apparently thrived during its time. Stegosaurus is also famous for a "second brain" in its hip region that may have controlled its hind legs and tail. Everything that is known about dinosaur brains is based on fossilized casts that formed when mud filled their skulls. A fossilized cast is a nearly perfect stone replica of a dinosaur brain -- minute details such as nerve endings are visible. Not all dinosaurs had minuscule brains. In relation to their body mass, ceratopsians had relatively large brains, as did such theropods as the dromaeosaurids. Dromaeosaurids, in fact, are considered to be the smartest of dinosaurs, and they were probably at least as intelligent as the Emu (a modern, ostrich-like bird). See also Sensory Perception See also Intelligence

Dinosaur Diet
We know what dinosaurs ate, or at least what class of food they ate, by the shape and condition of their teeth. Some dinosaurs had sharp teeth with serrations, and these were the teeth of meat eaters. Other dinosaurs had flat teeth for grinding leaves and needles of trees and bushes. Carnivores: Theropods were the meat-eaters. With large mouths and sharp, pointed teeth, they were able to swallow meat in unchewed hunks. Theropods include Tyrannosaurus and Allosaurus. Fossil evidence has been found showing Allosaurus tooth marks on Apatosaurus bones. Herbivores: Most of the remaining dinosaurs ate plants. Hadrosaurs typically ate leaves, twigs, pine needles, seeds, and fruit. This dietary analysis is based on actual fossilized stomach contents. Ceratopsians and ankylosaurs ate the leaves of smaller trees and low growing plants. The giant sauropods ate twigs and pine needles, fir, and sequoia tree tops. Omnivores: A few dinosaurs, such as the segnosaurids, may have eaten both meat and plants, although this is unconfirmed.

Dinosauria (Dinosaurs)
Translation: Terrible Lizards
In 1842, after several discoveries of strange, huge fossilized remains, Sir Richard Owen realized that the creatures were a hitherto unknown class of animals and coined the word Dinosauria (DYE-no-sawr-ee-ah), from the Greek deinos (terrible) and sauros (lizard). Actually, despite superficial resemblances, dinosaurs are not lizards at all. They belong instead to a larger group named Archosauria. Also included in Archosauria are birds and crocodiles. Dinosauria, therefore, refers in general to all the creatures known as dinosaurs. This "super order" can be broken into two major orders: Saurischia and Ornithischia. Saurischia and Ornithischia themselves are divided into suborders, and so on. Dinosaurs were an extremely successful form of life. They flourished for about 160 million years, from the Middle Triassic to Late Cretaceous Periods. Not all families or species of dinosaurs survived that entire span of time. About 66 million years ago, all species of dinosaurs but birds suddenly became extinct, and no one really knows why.

Dinosaurs with Armor
See Armor (Bony) Plating, Ankylosaurs, and Stegosaurs.

Diplodocidae (Diplodocids)
Translation: Double Beamed
Diplodocidae (dih-pluh-DOSS-ih-day) is a family of sauropods. They were called "double-beamed" because of the Y shapes on their tail vertebrae. Probably the extra bony material protected major arteries or allowed for the attachment of muscles. Diplodocids were quadrupedal herbivores whose teeth were peg-shaped. Members of the family could grow about 100 feet (30 meters) long, from head to tail. Diplodocids lived during the Late Jurassic Period. They have been discovered in North America, Europe, Asia, and Africa Apatosaurus, Diplodocus, Barosaurus, and Mamenchisaurus.

See Pachycephalosaurs

Dromaeosauridae (Dromaeosaurids)
Translation: Swift Lizards
Dromaeosauridae (droh-mee-o-SAWR-ih-day) is a family of Maniraptora theropods. These bipedal carnivores had large eyes and relatively large brains. They are considered to be among the most intelligent of dinosaurs. Although smaller than the carnosaurs, dromaeosaurids were fierce predators. Along with backwards-facing teeth (for slicing rather than biting), they sported 5 - 12 inch (12-cm - 30-cm) sickle-like claws on their toes. Dromaeosaurids lived during the Early to Late Cretaceous Periods. Their fossil remains have been found in North America, Asia, and South America. Adasaurus, Deinonychus, Saurornitholestes, and Velociraptor.

Dromaeosaurs (DROM-ee-uh-sawrz)
See Dromaeosaurids

Dryosauridae (Dryosaurids)
Translation: Oak Lizards
Dryosauridae (dry-o-SAW-ri-day) is a family of Iguanodontia, members of which were moderate-to-large sized bipedal herbivores. They had sharp, ridged molars; hands bearing five fingers; and long, reinforced tails.

Dryptosauridae (Dryptosaurids)
Translation: Tearing Lizards
Dryptosauridae (DRIP-tuh-sawr-us) is a family of Theropoda, members of which were large and once thought to resemble to tyrannosaurids. Despite their size, however, dryptosaurids share more structural similarities with the smaller and daintier coelurosaurids.

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