Camarasaurus (pronounce /ˌkæmərəˈsɔrəs/ KAM-uh-ruh-SAWR-us) meaning 'chambered lizard', referring to the holes in its vertebrae (Greek kamara meaning 'vaulted chamber', or anything with an arched cover, and sauros meaning 'lizard') was a genus of quadrupedal, herbivorous dinosaurs. It was the most common of the giant sauropods to be found in North America but only average in size: about 18 meters (60 ft) in length as adults, and weighing up to 18 tonnes (19.8 tons). It lived in the Late Jurassic Period, between 155 and 145 million years ago.