The end of the mesozoic era brought an astounding variety of dinosaurs to the world. For most of the Mesozoic Era (2.52 to 66 million years ago), reptiles known as dinosaurs were the dominant land animals on Earth. They thrived for nearly 180 million years. The remains, or footprints, of dinosaurs were first discovered in the early 19th century. Since then, dinosaur fossils have been found on every continent, including Antarctica. At least 1,000 species of dinosaurs have been identified. Dinosaurs were diverse animals with vastly different lifestyles and adaptations. These include carnivores and herbivores, animals that walk on two and four legs, and animals that live alone and in groups. Fossil evidence shows that dinosaurs ranged in size from smaller than a chicken to more than ten times larger than the largest elephant. By examining dinosaur remains, scientists have concluded that dinosaurs were ancient relatives of modern crocodiles, snakes, lizards and birds. Although most dinosaurs became extinct about 66 million years ago, one lineage of dinosaurs evolved into birds about 150 million years ago.