Ohmdenosaurus

Ohmdenosaurus, tibia with tarsus

• Germany, Baden- Württemberg ( Posidonia )

• Ohmdenosaurus liasicus

Ohmdenosaurus is a dinosaur from the group of sauropods. The only previously assigned style is Ohmdenosaurus liasicus. He is only known from three limb bones come from the Posidonia Shale ( Toarcian, Lower Jurassic ) of Baden- Württemberg. It was a quadrupedes and 3-4 m in length relative to other sauropods very small animal.

History of Research

The paleontologist Rupert Wild became aware in the seventies referred to as a plesiosaur humerus (upper arm ) Fossil, which is exhibited in the Museum Hauff in wood grubs. Wild realized that it could not involve the bones of a Plesiosaur, but the bones of a dinosaur. The exact origin of the fossil, which had long been part of the museum's own collection, could not be more clarified. It came from some spilled quarry near Ohmden. The lower part of the fossil, however, is still surrounded by rocks, so the exact sequence of rock, from which it comes, could be determined. In 1978, it was then described as Ohmdenosaurus liasicus of wild scientifically. The genus name means " lizard from Ohmden " which Artepithethon plays on the Lias, the geologic succession of Early Jurassic to.

Description of the findings

The material consists of bones of the right hind leg: The right tibia ( the shin bone), the astragalus and the calcaneus ( foot bones ), all of which protrude from a single rocks - but it is not, this is the natural bone union. The at the longest 405 mm measured tibia is freed up on the lower ( distal ) end completely from the rock. The ends are significantly weathered, in some places is also the highest ( perichondral ) layer of bone destroyed by the preparation. The tibia is generally compact and stocky and strongly thickened at the ends. A comb ( the crista lateralis) is interpreted as an approach to muscles. The lower end ( condyles ) is clear in the two condyles divided, however, are significantly down in height. The astragalus, a joint bone that sits directly in the living animal under the tibia and this is adapted, is described in the description as " sandal -shaped". At the longest point it measures 140 mm. A groove on the top was probably an approach for ligaments of the ankle. The small calcaneus is in addition to the much larger Astragalus at the distal end of the fibula ( calf bone ) located directly in the life of the animal. As with the ends of the tibia and the astragalus, the surface is rough and furrowed, suggesting that these areas were once surrounded by cartilage.

Under the tibia are in the rock " several 5-30 mm wide, oblong or round and partly merge into each bony structure " (wild ). Wild thinks it could be explained by Sehnenverknöcherungen. On the weathered sites of fossils further could frequently the worm Coelodiscus be detected, which is considered aasfressend since it was mostly detected at such sites on vertebrate fossils.

Paleopathology

The palaeopathology deals with how an animal was killed and how his bones reached the site of deposition. The Posidonia Shale of origin of the Fund consists of marine deposits - the next country was probably at least 100 km to the southeast. Isolated finds of land plants and pterosaurs ( Pterosauria ) in Posidonia also point to the country.

The tibia is different from other fossils from the Posidonia is that clear signs of weathering are visible. These are due to the lack of deep currents usually not available. Therefore, it is assumed that the bone were transported and immersed twice. It is believed that the dead animal after it died, was washed up on a beach or river delta, maybe even into the water. The tibia and the joint bones were half covered by sediments, followed by the highly weathered condylar point that stick out most of the sediment. After the bones were transported either by a strong storm or by carrion-eating reptiles into the sea up to the final location. Until then, tissue residues were still present, and then the fact that the bones lay together and the carrion-eating snail Coelodiscus point.

Relationships

In Ohmdenosaurus it is a very early, basal sauropods. Wild compared the findings into his studies later sauropods like Cetiosaurus and prosauropods as Plateosaurus. After wild it was a purely quadrupedal sauropods, since the upper articular surface of the tibia is aligned horizontally and thus acted to a columnar leg. Also, the processus ascendes missing on Astragalus, occurring in many partially bipedal prosauropods. On the other hand, he saw in the stepped condyles and the " sandal -shaped " Astragalus common with the prosauropods. Overall, he comes to the conclusion that Ohmdenosaurus must be made more likely to sauropods, where he represents a new family.

Today, more primitive sauropods are known. He was compared to Vulcanodon, which has a very similar tibia - differences lie in the astragalus, which is more compressed laterally at Ohmdenosaurus and has a unique among sauropods curvature. Often Ohmdenosaurus is therefore placed in the Vulcanodontidae family, although this is not considered safe.