| Named By: | Othniel Charles Marsh in 1890 |
| Time Period: | Late Jurassic, 152-150 Ma |
| Location: | USA, including the states of Colorado, Oklahoma, South Dakota, Utah and Wyoming - Morrison Formation |
| Size: | Up to about 27.5 meters long (based upon ROM 3670) |
| Diet: | Herbivore |
| Fossil(s): | Partial post cranial remains of several individuals |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropodomorpha | Sauropoda | Diplodocidae | Diplodocinae | |
| Also known as: | | Barosaurus affinis | |
Barosaurus ( BARR-o-SAWR-as) was a giant, long-tailed, long-necked, plant-eating dinosaur closely related to the more familiar Diplodocus. Remains have been found in the Morrison Formation from the Upper Jurassic Period of Utah and South Dakota (and possibly Africa, as exemplified by the Kadsi Formation). It is present in stratigraphic zones 2-5.
The composite term Barosaurus comes from the Greek words barys (barus) meaning "heavy" and sauros (sauros) meaning "lizard"; thus "heavy lizard".