| Named By: | Octavio Mateus & Miguel Telles Antunes in 2003 |
| Time Period: | Late Jurassic, 152 Ma |
| Location: | Portugal - Lourinha Formation |
| Size: | Estimated up to 25 meters long |
| Diet: | Herbivore |
| Fossil(s): | Partial post cranial remains mainly of vertebrae and some elements of the limb bones. No skull is so far known |
| Classification: | | Chordata | Reptilia | Dinosauria | Saurischia | Sauropodomorpha | Sauropoda | Brachiosauridae | |
| Also known as: | | Brachiosaurus atalaiensis | |
Lusotitan is a genus of herbivorous brachiosaurid sauropod dinosaur from the Late Jurassic Period of Portugal.
In 1947 Manuel de Matos, a member of the Geological Survey of Portugal, discovered large sauropod fossils in the Portuguese Lourinha Formation that date back to the Tithonian stage of the Late Jurassic period. In 1957 Albert-Felix de Lapparent and Georges Zbyszewski named the remains as a new species of Brachiosaurus: Brachiosaurus atalaiensis. The specific name referred to the site Atalaia. In 2003 Octavio Mateus and Miguel Telles Antunes named it as a separate genus: Lusotitan. The type species is Lusotitan atalaiensis. The generic name is derived from Luso, the Latin name for an inhabitant of Lusitania, and from the Greek word "Titan", a mythological giant.
The finds consisted of a partial skeleton lacking the skull and individual vertebrae uncovered in several locations. De Lapparent did not assign a holotype. In 2003 Mateus chose the skeleton as the lectotype. Its bones have the inventory numbers MIGM 4798, 4801-10, 4938, 4944, 4950, 4952, 4958, 4964-6, 4981-2, 4985, 8807, and 8793-5. These remains include 28 vertebrae and elements of the appendicular skeleton.
It has been estimated that Lusotitan was 25 meters (82 feet) long. It had long forearms, one of the reasons Mateus assigned it to the Brachiosauridae.
The lectotype was re-described by Mannion and colleagues in 2013.