The term Dinosauria refers to a nearly extinct group of vertebrates. This group arose from the reptiles in the late Middle Triassic Period and flourished from 240 to 65 million years ago during the Mesozoic Era. Most dinosaur suborders became extinct by the end of the Cretaceous Period. Dinosaurs differ from reptiles in the distinct division of the vertebral column; reduction of the hand, and alterations to the hip, knee, shin, ankle and foot. These modifications allowed a sometimes bipedal, upright and more mobile posture. Dinosaurs wereprobably, to varying degrees, warm-blooded (endothermic). The only living representatives of the Dinosauria are birds.

Varied Forms

It is useful to divide Dinosauria into three groups: theropods, sauropods and ornithischians. Theropods include the carnivorous Tyrannosaurus, Deinonychus and Ornithomimus, as well as Archaeopteryx and birds. The herbivorous sauropods include the giant diplodocids and brachiosaurs, and the earlier prosauropods. Ceratopsians, ornithopods, stegosaurs, ankylosaurs and pachycephalosaurs belong within the plant-eating ornithischian group. Most extinct dinosaurs had a thick skin covered with small bumps or tubercles. Dinosaurs range in size from the tiny hummingbird to the monstrous "Seismosaurus", more than 100 feet long.

Dinosaurs
 - STAN the T. rex
 - SUE the T. rex
 - T. rex specimen chart
 - Acrocanthosaurus
 - CLAWS Struthiomimus
 - Horned Dinosaurs
 - KELSEY Triceratops
 - Edmontosaurus

Birds
 - Fossil Birds

Vertebrates
 - Mammals
 - Dinosaurs & Birds
 - Reptiles & Amphibians
 - Fishes

Invertebrates
 - Mollusks
 - Echinoderms
 - Arthropods

 - Plants & Amber

 - Minerals
 - Meteorites
 - Geology

Much confusion about dinosaurs has arisen in popular and scientific literature. Many reptiles and even large mammals have been incorrectly thought of as dinosaurs. The characteristics that define dinosaurs exclude such animals as mammoths, plesiosaurs, crocodiles, mosasaurs, synapsids (like Dimetrodon), icthyosaurs and probably, pterosaurs. With the exception of a few birds, dinosaurs are non-aquatic.

Dinosaur teeth and skulls tell a story of adaptability. Most carnivores possessed a specialized dentition of serrated teeth that were designed like "steak knives" for killing and cutting up their prey. Some, like the birds and Ornithomimus, lost the ability to grow teeth. The "rod-like" teeth of sauropods enabled them to strip foliage from woody stems. Digestion was aided by the presence of gizzard stones. The most specialized dentitions developed in the ornithischian dinosaurs. Ornithischians had horny beaks, elaborate batteries of teeth and moveable jaw elements. These, combined with the swallowing of shed teeth to aid in digestion, gave them a very efficient "milling" system for processing vegetation.

Probably the most interesting development in recent dinosaur studies is an understanding of dinosaur "lifestyles". It seems fairly certain that most dinosaurs laid eggs and that some provided parental care to the nest and hatchling dinosaurs. Many groups, particularly the "duck-billed" hadrosaurs, migrated in large herds of up to several thousand individuals. There is also evidence that some carnivorous dinosaurs may have hunted in packs. Rapid growth and internal regulation of body heat suggest a more active life for dinosaurs than was previously imagined.

Extinction

Dinosaur fossils have been found on every continent. Since the first dinosaur bones were discovered in the 1820's, humans have pondered the extinction of the dinosaurs. Why did so many members of a group successful for more than 150 million years, suddenly die out? Speculation has led to the formulation of more than 80 theories explaining this extinction. Most are untestable. Several facts must be considered. 1. There may have been a decline in the number of species of dinosaurs during the last 10 million years of the Mesozoic Era. 2. A large number of plant and animal species became extinct by the end of the Mesozoic Era. 3. The close of the Mesozoic Era was a time when mountain building and a global lowering of sea levels dramatically altered terrestrial and marine habitats. 4. Where sediments are preserved at the close of the Mesozoic Era, there seems to be a thin layer containing an anomalous amount of iridium. Was this extinction caused by a cataclysmic event such as an asteroid collision or was it only the end result of gradual change? Why birds survived and the other dinosaurs became extinct may forever remain a mystery.

Dinosaurs are the most popular exhibits in natural history museums throughout the world. These strange, wonderful beasts have inspired awe in generations of children and adults. Dinosaur exhibits are often the catalyst for stimulating an interest in the wonders of science. Dinosaurs bring out those feelings that encourage each of us to imagine what these creatures were like and what has occurred on Earth over the course of time. They remind us that life is always changing and that, like most of the dinosaurs, we will also one day become extinct.

The Black Hills Institute has a variety of quality dinosaurs and replicas available for sale. Anyone from a private collector to an internationl museum will find something that suits their needs.