Ohmdenosaurus
| Ohmdenosaurus | ||||||||||||
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Ohmdenosaurus , shin with tarsus |
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| Temporal occurrence | ||||||||||||
| Lower Jurassic (Middle Toarcian ) | ||||||||||||
| 180 to 174.1 million years | ||||||||||||
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| Scientific name | ||||||||||||
| Ohmdenosaurus | ||||||||||||
| Wild , 1978 | ||||||||||||
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Ohmdenosaurus is a dinosaur belonging to the sauropod group . The only species assigned to date is Ohmdenosaurus liasicus . It is only known from three extremity bones, which come from the Posidonia schist ( Toarcium , Lower Jurassic ) from Baden-Württemberg . It was a quadruped animal, 3–4 m long compared to other sauropods.
Research history
Paleontologist Rupert Wild was in the 1970s as a plesiosaur - humerus carefully designated (upper arm) Fossil, which the Museum Hauff in Holzmaden is issued. Wild realized that it couldn't be the bone of a plesiosaur but the bone of a dinosaur. The exact origin of the fossil, which had long been part of the museum's own collection, could no longer be clarified. It came from some buried quarry near Ohmden . However, the lower part of the fossil is still surrounded by rocks, which is why the exact sequence of rocks from which it originated could be determined. Then in 1978 it was scientifically described as Ohmdenosaurus liasicus by Wild. The generic name means "Lizard from Ohmden", the epithet alludes to the Lias , the geological series of rocks of the early Jurassic.
Description of the find
The material consists of bones from the right hind leg: the right tibia (the shinbone), the astragalus and the calcaneus (foot bones), all of which protrude from a single lump of rock - however, this is not the natural bone structure. The tibia, measuring 405 mm at its longest point, has been completely cleared of rock except for the lower (distal) end. The ends are clearly weathered, in some places the top (perichondral) bone layer has also been destroyed by the preparation. The tibia is generally compact and stocky and greatly thickened at the ends. A crest (the lateral crista) is interpreted as the attachment for muscles. The lower end is clearly divided into the two articular knots (condyles), which are clearly graduated in height. The astragalus, a joint bone that sits directly under the tibia in living animals and is adapted to it, is described in the description as "sandal-shaped". At the longest point it measures 140 mm. A furrow on the top was likely an insertion for ligaments of the ankle. In the life of the animal, the small calcaneus is located directly next to the much larger astragalus at the distal end of the fibula (fibula). As with the ends of the tibia and the astragalus, the surface is rough and furrowed, suggesting that these areas were previously surrounded by cartilage.
Beneath the tibia lie in the rock "several 5–30 mm large, elongated or round and partly merging bony structures" (Wild). Wild says it could be tendon ossification. In addition, the snail Coelodiscus , which is considered to be scavenging, as it was predominantly found in such places on vertebrate fossils, could often be found in the weathered areas of the fossils .
Taphonomy
The taphonomy deals with the processes that took place after the death of the animal, especially the embedding and fossilization. The Posidonia schist from which the find was made consists of marine deposits - the nearest land was probably at least 100 km southeast. Isolated finds of terrestrial plants and pterosaurs (Pterosauria) in Posidonia also point to the country.
The tibia differs from other fossils of the Posidonia slate in that clear signs of weathering are visible. These usually do not occur due to the lack of deep currents. Therefore, it is believed that the bones were transported and embedded twice. It is believed that after the dead animal died, it was washed up on a beach or river delta, perhaps in the water. The tibia and articular bones were half covered by sediment, as indicated by the heavily weathered articular knots that are most likely to protrude from the sediment. Then the bones were transported into the sea to their final location, either by a strong storm or by scavenging reptiles. Tissue remnants were still present until then, as indicated by the fact that the bones were lying together and the scavenging snail Coelodiscus .
Kinship relationships
In ohmdenosaurus is a very early, basal sauropods. In his investigations, Wild compared the findings with later sauropods such as Cetiosaurus and with prosauropods such as Plateosaurus . According to Wild, it was a purely quadruped sauropod, since the upper articular surface of the tibia was aligned horizontally and it was therefore a columnar leg. The ascending process of the astragalus, which occurs in many partially bipedal prosauropods, is also absent. On the other hand, he saw in the graduated knot and the "sandal-shaped" astragalus similarities with the prosauropods. Overall, he comes to the conclusion that Ohmdenosaurus should rather be placed with the sauropods, where he represents a new family.
Today other primitive sauropods are known. It was compared with Vulcanodon , which has a very similar tibia - differences lie in the astragalus, which is more laterally compressed in Ohmdenosaurus and has a curvature that is unique among sauropods. Often, as a result, Ohmdenosaurus is placed in the Vulcanodontidae family , although this is not considered certain.
literature
- Rupert Wild : A sauropod remnant (Reptilia, Saurischia) from the Posidonia schist (Lias, Toarcium) from Holzmaden (= Stuttgart contributions to natural history. Series B: Geology and palaeontology. No. 41, ISSN 0341-0153 ). State Museum for Natural History, Stuttgart 1978.
Individual evidence
- ↑ David B. Weishampel , Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . University of California Press, Berkeley CA et al. 1990, ISBN 0-520-06726-6 .