The first find in 1957, a partial fossil skeleton found near Alenquer, was dubbed "Apatosaurus" alenquerensis by Lapparent and Zbyszewski. However, the find of another partial skeleton, including a tooth and 100 gastroliths, in co-eval strata near the town of Lourinhã in 1983, allowed the identification of the fossils as a distinct form from Apatosaurus, hence the generic name referring the new locality while the specific descriptor was carried over from the old designation.
Lourinhasaurus is an herbivorous dinosaur measuring an estimated 17 meters (56 feet) in length. It's characterized by the morphology of its first seven dorsal vertebrae with relatively high, bifurcated neural apophyses; also, the posterior cervical vertebrae have prominent ventral longitudinal keels on their centra. L. alenquerensis due to the lack of a skull is only classifiable as an eusauropod and it was found by Upchurch (2004) to be the sister taxon to Neosauropoda. It's thought it may have resembled Camarasaurus, albeit with proportionately longer forelimbs.
In the meantime a third fossil sauropod skeleton was discovered. It had passing similarities to Lourinhasaurus, thus being referred to the genus at first, but later was recognized as different enough to warrant a description under the genus Dinheirosaurus. For some time there was the possibility that these genera were synonymous, but further phylogenetic analysis dispelled such a notion.
Lourinhasaurus should not be confused with Lourinhanosaurus, a theropod dinosaur also found near Lourinhã.