Ohmdenosaurus ("Ohmden lizard") is a genus of sauropod dinosaur that lived during the Early Jurassic epoch in what is now Germany. The only specimen – a tibia (shinbone) and ankle – was discovered in rocks of the Posidonia Shale near Ohmden. The fossil was originally identified as a plesiosaur. Exhibited in a local museum, the Urweltmuseum Hauff, it caught the attention of German paleontologist Rupert Wild, who recognized it as the remains of a sauropod. Wild named Ohmdenosaurus in a 1978 publication, the only species is Ohmdenosaurus liasicus. One of the earliest known sauropods, it was quadrupedal (four-legged) and already had the columnar limbs typical for the group. Ohmdenosaurus was small for a sauropod, with an estimated length of . Its relationships to other sauropods remain poorly known due to the incompleteness of its remains, though it might have been close to the Australian genus Rhoetosaurus. The Posidonia Shale was deposited within a shallow inland sea and contained abundant and well-preserved fossils of marine reptiles including ichthyosaurs and plesiosaurs. Ohmdenosaurus was a terrestrial animal, and its carcass must have been transported by predators or water currents by at least from the shoreline to its site of burial. It is the only dinosaur fossil known from the shale. History of discovery The Posidonia Shale at Holzmaden in southwestern Germany is one of the world's major fossil Lagerstätten (fossil deposit of exceptional importance). Deposited within an inland sea, it contains abundant marine reptiles such as ichthyosaurs, plesiosaurs, and crocodyliforms, sometimes with soft tissue preservation. This organic-rich shale has been quarried for more than 400 years, first for roofing and paving, and later also to extract oil. Its exceptionally preserved fossils were made famous by Bernhard Hauff, who started to collect and prepare specimens found in a quarry owned by his father. In 1862, Hauff presented an ichthyosaur specimen that still preserves the original body outline, revealing that ichthyosaurs possessed dorsal fins. Together with his son, he opened a local museum in Holzmaden in 1936/37, the Urweltmuseum Hauff, to display the finds. In the 1970s, German paleontologist Rupert Wild, while visiting the Urweltmuseum Hauff, noticed a fossil in a display labelled as an upper arm bone of a plesiosaur. Wild recognized the specimen as a misidentified dinosaur fossil, borrowed the specimen for study and conducted additional preparation. The fossil, which lacks a specimen number, consists of a right tibia (shinbone) together with the