Aardonyx
Artistic live representation of Aardonyx
- Free State, South Africa ( Elliot Formation)
- Aardonyx celestae
Aardonyx ( Afrikaans aard - "Earth" and Greek Onux - "claw ") is a basal ( original ) genus of dinosaur sauropodomorphen. So far, the remains of probably two individuals are known to have been recovered from the Lower Jurassic strata of the Elliot Formation in South Africa. Aardonyx was described in 2010 by researchers at Adam Yates for the first time scientifically. The only way is Aardonyx celestae. Although Aardonyx probably two being ( biped ) was, he already shows a number of features that were characteristic of the four-footed ( quadrupedal ) sauropods. As an important transitional form this species contributed to the understanding of the evolution of Quadrupedie within the Sauropodomorpha at.
Description
Aardonyx was probably bipedal running herbivore with a long neck and small head. The skulls of the specimens found are estimated to have a length of about 36 centimeters. Seen from above, the skull shows a narrow, pointed snout. From allied genera it differs inter alia by the large nostrils, which were at least as large as the eye sockets, as well as the five teeth in the premaxillary bone ( premaxilla ) - a feature that has evolved independently in Plateosaurus. On each side of the upper jaw ( maxilla ) were about 18 teeth, while the lower jaw ( dentary ) on each side more than 19 teeth had. The cervical vertebrae were long and low. The limbs have a bipedal locomotion, but already show adaptations to a four-legged locomotion, as found in the later sauropods. Thus, the foot bones are relatively short and robust, in particular the first metatarsal was particularly robust.
Discovery
Aardonyx is known from disarticulated ( not present in the context ) bones, probably of two subadult ( immature ) individuals come. The remains were found in Senekal in South Africa's Free State province within a former infilled river bed. They consist of skull elements, vertebrae, back and neck ribs, abdominal ribs, Chevronknochen, elements of the shoulder and pelvic girdle and bones of the front and hind limbs, the hand and the foot. The carcasses were ahead of their embedding likely to be relatively complete, and were not transported very far from the water: So fragile skull bones have been preserved in addition to massive bone, a rejection by the flow so did not take place. Both individuals were probably less than 10 years old at her death. Bone cross-sections show concentric growth zones, which alternate with rings, the times of arrested growth (Show engl. rest lines). Since none of the examined bone off from the outside with such a reduced ring growth, it can be concluded that the animals were still in active growth.
Paleoecology
The fossils date from the Upper Elliot Formation, a rich fossil site, which is open in South Africa and Lesotho. It is part of the Stormberg Group of the Karoo Supergroup. Aardonyx shared its habitat with the more primitive Sauropodomorphen Massospondylus and early sauropod. Other dinosaurs of the Upper Elliot Formation close the Heterodontosauriden Heterodontosaurus, Abrictosaurus and Lycorhinus and the Cerato dinosaur with a Megapnosaurus.
System
Plateosauridae
Riojasauridae
Gryponyx
Massospondylidae
Yunnanosaurus
Jingshanosaurus
Aardonyx
Eusauropoda
Aardonyx is a basal representative of the Anchisauria within the Sauropodomorpha. He is one of the classic prosauropods, a designation for basal Sauropodomorpha outside the sauropods. Since the prosauropods not represent natural groups ( paraphyletic ), the name is today hardly use more. An analysis of Yates and colleagues (2010 ) provides Aardonyx as sister taxon of a clade Melanorosaurus and the sauropods contains. Representatives of this clade were consistently obligate quadrupedal running ( quadruped ). Thus Aardonyx is the closest related to the sauropod genus, which was itself still bipedal ( biped ). It represents a transitional form between the basal bipedal and quadrupedal sauropods Sauropodomorpha dar.
Paleobiology
Nutrition
Basal Sauropodomorphen had narrow, V-shaped tapered jaws and probably fleshy cheeks. Sauropods, however, show adjustments that the rapid uptake of larger quantities of food allowed ( engl. bulk -browsing ): Thus, the jaws were wide and U- shaped, which allowed a wider bite while cheeks were missing. The racks were reinforced by internal plates through which support the teeth in stripping leaves. Aardonyx shows an interesting combination of these characteristics: while the pine zuliefen pointed, cheeks seem to have been missing. In contrast, the basal sauropod Chinshakiangosaurus shows a reverse combination: This sauropod had fleshy cheeks, but already had the U-shaped teeth. The researchers suggest that the development towards the bulk -browsing of sauropods was not straight, but that some features are repeatedly arisen independently ( homoplasy ).
Locomotion
Features of the limbs of Aardonyx indicate a bipedal stride. So the head of the radius ( radius) was ovoid, which restricted rotation of this bone to the ulna ( ulna ). Thus, the animal could not pronate the forearm ( turning inward ), so that the palms could not be aligned pointing down. In addition, the upper arm bone made from (humerus ) only 72 % of the length of the thigh bone (femur).
Other features on the arm and leg bones are, however, considered as adaptations to a more quadrupede locomotion. Example, shows the upper end of the ulna a craniolateralen comb, which can appear Elle viewed from above Y -shaped. Such comb is also found in the quadrupedal sauropods, but where it is more pronounced. In the spoke Furthermore allowed a depression ( fossa ) a craniolaterale movement of the ulna. The hind legs show some adjustments to a quadrupede locomotion. Thus, the shaft of the femur is straight, while the fourth trochanter, one serving as muscle attachment point spinous process, below (distal ) is positioned as in more basal Sauropodomorphen. This allowed the Caudofemoralis, the most important Zugmuskel of the thigh, a larger lever arm and thus more power, but at the same time made him slower. Consequently Aardonyx was less rapidly than typical basal Sauropodomorpha.
Another, speaking for a slower locomotion feature was the robustness of the first metatarsal in comparison with other basal Sauropodomorpha. This suggests that body weight was not focused on the middle toe ( mesaxonic ), as in basal Sauropodomorpha, but that the weight-bearing axis was more shifted towards the center of the foot down ( entaxonic ). This shift also points out that the legs were splayed outward somewhat more than in basal Sauropodomorpha; an adjustment which is probably preceded by the obligatory Quadrupedie in evolution. Previously it was assumed that the weight-bearing axis has shifted only when the animals were already quadruped. So shows the early sauropod Vulcanodon, although obligate quadruped, a mesaxonischen foot - a feature that could be interpreted in light of the discovery of Aardonyx as evolutionary reversal.