Archaeodontosaurus

Tooth ( different views of the same specimen )

• Madagascar ( Isalo IIIb Formation)

• Archaeodontosaurus descouensi

Archaeodontosaurus is a genus of dinosaurs and a very original representatives of the sauropods. Previously, a jawbone ( dentary ) is only known with some teeth, which dates from the Middle Jurassic ( Bathonian ) of Madagascar. The teeth were very earthy and were similar to those of the precursor of the sauropods ( the " prosauropods " ), while the jawbone was followed by the progressive, typical for sauropods blueprint. This combination is very unusual for early sauropods - mostly we find the reverse combination with a prosauropods -like jaw and sauropod - like teeth. Such a reversal of advanced and original features is referred to in evolutionary biology as a mosaic evolution. This genus is important for understanding the early evolution of sauropods of meaning and can mosaic evolution suggests early development in different lines of this group. Archaeodontosaurus 2005 was described by the French paleontologist Eric Buffetaut scientifically, the only way is Archaeodontosaurus descouensi.

Features

The only fund consists of a right dentary ( the tooth-bearing bone of the lower jaw ), but the the front and the rear end is missing. The preserved part of the bone measures 18.7 cm in length and has a maximum depth of 6.4 cm. There are get 16 dental trays, maybe it was some more on the non-preserved ends of the bone. Teeth or tooth fragments have been preserved in 8 of these alveoli, all teeth obtained were not yet erupted. Since the top, pointing to the inner edge of the dentary is poorly preserved, the teeth are on the inside partially free.

The Dental follows the typical sauropod anatomy: So, the depth of this bone to the front clearly, indicating ( the seam of the two mandibular halves ) on a deep symphysis. In addition, in particular the front section of this bone was bent inward, which suggests that the jaw formed the typical for sauropods U-shaped teeth. The prosauropods the jaw, however, were straight and ran viewed from above V-shaped toward each other.

The tooth crowns, however, were similar to those of prosauropods more than those of other sauropods. They were viewed from the side leaf-shaped and ran up to pointed, while the other sauropods were mostly spatulate. In addition, the crowns were on the side facing the tongue side bowed outwards ( convex) - the other sauropods, however, were curved inward ( concave) and thus spoon-shaped. In addition, the crowns were cut at Archaeodontosaurus with at least 11 large teeth, another original feature. However, the enamel was folded as in other sauropods - at prosauropods he was smooth.

Comparisons and systematics

Comparisons with other very early sauropods are very limited because the skull bones are rarely preserved. Jawbone are known from the early sauropods Kunmingosaurus, Shunosaurus, Chinshakiangosaurus, Tazoudasaurus and Protognathosaurus. Kunmingosaurus shows a deep lower jaw and spatulate teeth and thus corresponds to the later sauropods. Shunosaurus shows laterally flattened teeth that were not spoon-shaped as in later sauropods; the mandible was not particularly deep. Chinshakiangosaurus resembled Archaeodontosaurus in the morphology of the jaw. The teeth also had a prosauropodenartiges appearance, however, were on the side facing the tongue side partly been concave. Tazoudasaurus however, shows spatulate teeth, but slender pine, similar to those of prosauropods. The only form that has a similar combination of features such as Archaeodontosaurus, is the Chinese Protognathosaurus: In this form, the teeth were, however, more spatulate than in Archaeodontosaurus and showed 8 to 10 teeth.

Since Archaeodontosaurus has survived only sparsely, and because comparable fossils of other early sauropods are rare, the systematic position of this genus within the sauropods can not presently be determined.

Fund and naming

The fossil dates from around Ambondromamy, a village in the valley of Kamoro southwest of Mahajanga. It comes from the sand - and mudstones of the Isalo IIIb formation, which can be dated to the Bathonian. The name Archaeodontosaurus ( gr archaios - " old " Odous - "tooth", sauros - " lizard" ), has its original, prosauropodenartige morphology of the teeth. The species name honors descouensi Didier Descouenses from Toulouse, which handed over the fund to the Musée d' Histoire naturelle, the Natural History Museum in Toulouse and thus made ​​accessible to science.