| Diet | Herbivore |
| Height | 5m |
| Length | 33m |
| Weight | 35 tonnes |
| Speed | 15 km/h |
| Environment | Land |
| Era | Jurassic |
| Period | Late Jurassic |
| Type | Sauropod |
| Location | North America |
Although originally described as a separate genus in 1991, Seismosaurus is now considered to be the same species as Diplodocus longus, making it a junior synonym of the famous long-necked dinosaur. This massive sauropod lived during the Late Jurassic period, between 158 and 149 million years ago, in what is now the western United States.
When first discovered, Seismosaurus was thought to be one of the longest dinosaurs ever found, with estimates reaching up to 33 metres in length and weighing around 35 tonnes. This enormous sauropod had the classic diplodocid body plan: an exceptionally long neck with at least 15 vertebrae, a relatively small head, a barrel-shaped body supported by four pillar-like legs, and an incredibly long, whip-like tail that made up much of its total length.
As a herbivore, this giant dinosaur would have used its long neck to reach vegetation at various heights, from ground-level ferns and cycads to the tops of tall conifer trees. Its teeth were simple pegs designed for stripping leaves rather than chewing, so it likely swallowed stones to help grind up plant material in its massive stomach.
The creature inhabited the lush floodplains and river systems of Late Jurassic North America, sharing its environment with other famous dinosaurs like Allosaurus, Stegosaurus, and other sauropods including Camarasaurus and Brontosaurus.
Seismosaurus possessed an extraordinarily long, whip-like tail that could exceed 14 metres in length, making up nearly half of its total body length. Its neck was remarkably elongated with at least 15 cervical vertebrae, allowing it to reach vegetation up to 17 metres above ground level.
This massive sauropod likely lived in small herds and migrated seasonally to follow food sources across the Late Jurassic landscape. Its long tail may have been used as a defensive weapon, capable of creating sonic booms when snapped like a whip to deter predators such as Allosaurus.
Seismosaurus has appeared in several dinosaur documentaries and educational programmes, often highlighted as an example of the extreme sizes that dinosaurs could reach.
Seismosaurus was first described by David Gillette in 1991. The original fossils were discovered at Morrison Formation, New Mexico, USA.
