Apatosaurus (IPA: /əˌpætəˈsɔrəs/), popularly (though incorrectly) known as Brontosaurus, is a genus of sauropod dinosaur that lived about 140 million years ago, during the Jurassic Period. It was one of the largest land animals that ever existed, with an average length of 23 metres (75 ft) and a mass of at least 23 metric tons (25 short tons). The name Apatosaurus means 'deceptive lizard', so-given because the chevron bones were similar to those of Mosasaurus (Greek ἀπατέλος or ἀπατέλιος meaning 'deceptive' and σαῦρος meaning 'lizard'). The cervical vertebrae were less elongated and more heavily constructed than those of Diplodocus and the bones of the leg were much stockier (despite being longer), implying a more robust animal. The tail was held above the ground during normal locomotion. Like most sauropods, Apatosaurus had only a single large claw on each forelimb, with the first three toes on the hindlimb possessing claws.