The dinosaurs went extinct about 65 million years ago, at the end of the Cretaceous period, which was a time of high volcanic and tectonic activity. The most widely accepted theory is that an asteroid impact caused major climactic changes to which the dinosaurs couldn't adapt. Although dinosaurs' fossils have been known since at least 1818, the term dinosaur (deinos means terrifying; sauros means
lizard) was coined by the English anatomist Sir Richard Owen in 1842
The oldest known dinosaur is Eoraptor, a meat-eater from about 228 million years ago
Every few months (sometimes weeks), new finds are unearthed. There are almost 500 described dinosaur genera and many more species. Some dinosaurs were very bird-like and may be the ancestors of today's
birds
The dinosaurs went extinct 65 million years ago, probably because of the environmental changes brought about by an asteroid hitting the Earth. Dinosaurs were reptiles and most hatched from eggs. The largest dinosaurs were over 100 feet (30 m) long and up to 50 feet (15 m) tall (like Argentinosaurus, Seismosaurus, Ultrasauros, Brachiosaurus, and Supersaurus). The smallest dinosaurs, like Compsognathus, were about the size of a chicken. Most dinosaurs were in-between. Some dinosaurs were meat-eaters (also called carnivores). For example, T. rex was a meat-eating dinosaur. Most dinosaurs were plant-eaters (also called herbivores). For example, Triceratops was a plant-eating dinosaur. There were lots of different kinds of dinosaurs that lived at different times.
• Some walked on two legs (they were bipedal), some walked on four (they were quadrupedal). Some could do both.
• Some were speedy (like Velociraptor), and some were slow and lumbering (like Ankylosaurus).
• Some were armor-plated, some had horns, crests, spikes, or frills.
• Some had thick, bumpy skin, and some even had primitive feathers. Rajasaurus narmadensis
When paleontologists Paul Sereno and Jeff Wilson arrived in India in 2001 to study a mixed collection of dinosaur bones gathered by Indian scientists 18 years earlier, they found the bones spread out on an office floor. Sifting through the collection, they separated out the bones of a theropod, or meat-eating dinosaur. When they found the center part of a skull, they recognized a horn resembling those of dinosaurs found in Madagascar. Their search continued, yielding a left hip, then a right hip, then a sacrum. Sereno and Wilson consulted detailed, hand-drawn maps drafted by their Indian counterparts and discovered the bones had been buried next to each other, as if they had been connected. "There was a Eureka! moment when we realized we had a partial skeleton of an undiscovered species," said Sereno, a paleontology professor at the University of Chicago and a National Geographic Explorer-in-Residence. The bones were collected in 1983 by Suresh Srivastava of the Geological Survey of India (GSI) and Ashok Sahni, a paleontologist at Panjab University, during a search for dinosaur eggs and nests. Srivastava drew a detailed map to document the position of the fossil bones as they lay in the field. The scientists then stored the 65-million-year-old bones at a GSI office, where they stayed until Sereno and Wilson arrived. Working with Indian experts, Wilson and Sereno reconstructed the skull of the new species, a stocky, 30-foot-long (9-meter-long) carnivore named Rajasaurus narmadensis, which means "regal dinosaur from the Narmada," the river region in western India where the bones were found. The project was supported in part by the National Geographic Society. "We knew of fragments and bones [in India]," said Sereno, who has discovered new dinosaur species on five continents. "But this skull reconstruction offers the first glimpse into the lost world of the Indian dinosaur." There were already two Jurassic dinosaur skeletons mounted in India. Neither, however, represents a single skeleton, but is instead based on composites of isolated bones. "We know that there were carnivorous and herbivorous dinosaurs in India through individual bones, but we really don't know just how they looked because no two bones can be reliably said to belong to one individual," said Wilson, who is of the University of Michigan. "Rajasaurus is important because it represents a partial skeleton and preserves many details that clue us into its evolutionary relationships." The reconstructed skull is missing some parts, but it has the most important pieces: the jaws and the brain case. Between 25 and 30 feet (7.6 and 9 meters) long, the Rajasaurus was heavy and strong, and walked on two legs. "There are several anatomical details that make Rajasaurus a new species," said Wilson. "Perhaps the most striking is the horn it bears on its head. The horn was probably rather subtle. It may have been low and rounded." The carnivorous Rajasaurus, which lived in the Cretaceous Period at the end of the dinosaur age, preyed on long-necked titanosaur sauropods, herbivorous dinosaurs that also roamed the Narmada region. Bones from both dinosaurs were found together. Indian paleontologists recently found coprolites (fossilized dung) that provide additional clues to the diet of those titanosaurs. "Large theropod eggs have also been described by our group from the area where the skeleton of Rajasaurus has been recovered, but it's difficult to relate the theropod eggs specifically to Rajasaurus," said Sahni. The scientists believe the Rajasaurus is related to a family of large carnivorous dinosaurs, most of which had horns, that roamed the southern hemisphere land masses of present Madagascar, Africa, and South America. "People don't realize dinosaurs are the only large-bodied animal that lived, evolved, and died at a time when all continents were united," said Sereno. Continental Drift
The Rajasaurus was likely like its contemporary, Tyrannosaurus rex—one of the last species to live before a catastrophe occurred some 65 million years ago.
