You have learned about dinosaurs in school. Maybe you have seen them in museum. But how much do you really know about these animals?
Not all dinosaurs were just big reptiles. For years, scientists thought dinosaurs were big, dumb, and cold blooded - in other words, just giant reptiles. Some dinosaurs were huge. But many were about the size of modern-day birds or dogs. Were dinosaurs warm- or cold blooded? Paleontologists are not sure. But they believe some were intelligent. Of course, no dinosaur was as smart as a human or even a monkey. However, some smaller dinosaurs - like the two-meter (six-foot) Troodon - had fairly large brains.
Was Tyrannosaurus rex a powerful predator? Some scientists think the opposite is true. In the movies, T.rex is often a speedy giant, but in fact, this dinosaur could not run very fast. Physically, it was too large. In reality, T.rex probably moved as fast as an elephant. Also, T. rex had very small arms. Without strong legs or arms, this dinosaur probably wasn't a powerful hunter. It may have been a scavenger instead, only eating animals that were already dead.
Did an asteroid kill the dinosaurs? An asteroid hit Mexico's Yucantan Peninsula about 65 million years ago. It created a 180-kilometer (110-mile) wide crater called Chicxulub. Many believe this asteroid caused the extinction of the dinosaurs. But even before this, dinosaurs were already dying out around the world, for many reasons. At the end of the Cretaceous period, for example, the global climate was changing uc Earth's temperature was getting colder.
Dinosaurs completely disappeared about 65 million years ago. However, scientists believe modern-day birds are descendants of certain dinosaurs. If this true, then dinosaurs' relatives are still walking - and flying - among us!

Together, the thousands of scientists and conservation organizations that contribute to the International Union for Conservation of Nature (IUCN) Red List and other systems of assessment provide the world's largest knowledge base on the global status of species. The aim of these systems is to provide the general public, conservationists, nongovernmental organizations, the media, decision makers, and policy makers with comprehensive and scientifically rigorous information on the conservation status of the world's species and the threats that drive the observed patterns of population decline. Scientists in conservation and protected area management agencies use data on species status in the development of conservation planning and prioritization, the identification of important sites and species for dedicated conservation action and recovery planning, and educational programs. Although the IUCN Red List and other similar species-assessment tools do not prescribe the action to be taken, the data within the list are often used to inform legislation and policy and to determine conservation priorities at regional, national, and international levels. In contrast, the listing criteria of other categorization systems (such as the United States Endangered Species Act, the CITES) are prescriptive; they often require that landowners and various governmental agencies take specific mandatory steps to protect species falling within particular categories of threat
It is likely that many undescribed or unassessed species of plants, animals, and other organisms have become or are in the process of becoming extinct. To maintain healthy populations of both known and unknown species, assessments and reassessments are valuable tools. Such monitoring work must continue so that the most current knowledge can be applied to effective environmental monitoring and management efforts. For many threatened species, large well-protected conservation areas (biological reserves) often play major roles in curbing population declines. Such reserves are often cited by conservation biologists and other authorities as the best way to protect individual species as well as the ecosystems they inhabit. In addition, large biological reserves may harbor several undescribed and unassessed species. Despite the creation of several large reserves around the world, poaching and illegal trafficking plague many areas. Consequently, even species in those areas require continued monitored and periodic assessment.