Ohmdenosaurus (meaning "Ohmden lizard") is the name given to a genus of herbivorous dinosaur from the Early Jurassic. It was a very small (4 m (13 ft) long) perhaps vulcanodontid sauropod which lived in Germany. Only a couple of fragmentary leg bones were found.
Temporal range: Early Jurassic, Toarcian
In the 1970s, German palaeontologist Rupert Wild, visiting the Urwelt-Museum Hauff at Holzmaden, noticed a fossil in a display labelled as a plesiosaur which he recognised to be a dinosaur bone instead. It proved to be impossible to establish the exact provenance of the remains. In 1978 it was named and described by him as the type species Ohmdenosaurus liasicus. The generic name refers to Ohmden, a town in Baden-Württemberg near the quarry the remains were probably found in. The specific name refers to the Lias, an old name for the Early Jurassic.
The holotype, which lacked an inventory number, was apparently found in the famous Posidonia Shale, marine strata dating from the middle Toarcian, as can be established from the presence of the snail Coelodiscus in the matrix rock containing the only partially prepared bones. It consists of a right tibia, an astragalus and a calcaneus. The bones, disarticulated in the fossil, show signs of weathering, evidence that the animal died on land and that only later its bones were washed into the sea. The tibia is only 405 millimetres long, indicating a remarkably small individual for a sauropod.
The shape of the fourteen centimetres wide astragalus, like that of a sandal and not convex on top as with the derived Neosauropoda, proves that Ohmdenosaurus is a very basal sauropod. In 1990 John Stanton McIntosh classified Ohmdenosaurus in the Vulcanodontidae but that concept then functioned as a waste-basket taxon for all kinds of unrelated basal sauropods. It has not been confirmed by an exact analysis as a vulcanodontid in the modern sense.