English: Apatosaurus is a diplodocid sauropod that lived in North America during the Late Jurassic period. It was a large, long-necked animal supported by four pillar-like legs. Diplodocidae includes some of the longest creatures ever to walk the earth, with size estimates of Apatosaurus upwards of around 30 m in length and around 33 t in body mass. Trackways of sauropods like Apatosaurus show that they may have had a range of around 25–40 km per day, and that they could potentially have reached a top speed of 20–30 km per hour.