Aardonyx

Aardonyx
Artistic live presentation of aardonyx
Temporal occurrence
Lower Jurassic
195 million years
Locations
Free State , South Africa ( Elliot Formation )
Systematics
Ornithodira Dinosaur (dinosauria) Lizard dinosaur (Saurischia) Sauropodomorpha Anchisauria Aardonyx
Scientific name
Aardonyx
Yates et al. , 2010
Art
Aardonyx celestae

Aardonyx ( Afrikaans aard - "earth" and Greek onux - "claw") is a basal (original) genus of the sauropodomorphic dinosaur . So far, the remains of presumably two individuals are known thatwere recoveredfrom the sub-Jurassic layers of the Elliot Formation in South Africa . Aardonyx wasfirst scientifically described in 2010 by researchers led by Adam Yates . The only species is Aardonyx celestae . Although aardonyx was probably two-legged ( biped ), it already shows a number of features that were characteristic of the four-footed ( quadruped ) sauropods. As an important transition form, this genus contributed to the understanding of the evolution of the quadrupeds within the Sauropodomorpha.

description

Aardonyx in size comparison with a human

Aardonyx was a probably two-legged herbivore with a long neck and small skull. The skulls of the specimens found are estimated to be around 36 centimeters long. Seen from above, the skull shows a narrow, pointed snout. It differs from related genera, among other things, by the large nostrils, which were at least as large as the eye sockets, as well as by the five teeth in the intermaxillary bone (Os praemaxillare) - a characteristic that has developed independently in Plateosaurus . There were about 18 teeth on each side of the upper jaw (maxillary), while the lower jaw (dental) had more than 19 teeth on each side. The cervical vertebrae were long and low. The limbs show a two-legged locomotion, but already show adaptations to a four-legged locomotion, as found in the later sauropods. The foot bones are relatively short and robust, with the first metatarsal in particular being particularly robust.

Find

Aardonyx is known to be found in disarticulated (unrelated) bones believed to have come from two subadult (not yet fully grown) individuals. The remains were discovered in Senekal in the South African province of Free State within a former, filled river bed. They consist of skull elements, vertebrae, back and neck ribs, abdominal ribs , chevron bones , elements of the shoulder and pelvic girdle and bones of the fore and hind limbs, the hand and the foot. The cadavers were probably relatively complete before they were embedded and were not transported very far by the water: fragile skull bones have been preserved alongside more massive bones, so they were not sorted out by the current. Both individuals were likely less than 10 years old when they died. Bone cross-sections show concentric growth zones that alternate with rings that indicate times of reduced growth ( rest lines ). Since none of the examined bones ends externally with such a ring of reduced 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 deposit , which in South Africa and Lesotho minded is. She is part of the Stormberg group of the Karoo super group . Aardonyx shared its habitat with the more pristine sauropodomorph Massospondylus as well as early sauropods. Other dinosaurs of the Upper Elliot Formation include the heterodontosaurs Heterodontosaurus , Abrictosaurus and Lycorhinus as well as the ceratosaur Megapnosaurus .

Systematics

Sauropodomorpha  Plateosauridae     Riojasauridae     Gryponyx     Massospondylidae     Yunnanosaurus     Jingshanosaurus  Anchisauria  Anchisaurus     Aardonyx     Melanorosaurus  Sauropoda  Antetonitrus     Lessemsaurus     Gongxianosaurus    Tazoudasaurus     Vulcanodon     Eusauropoda Cladogram according to Yates et al.

Aardonyx is a basal representative of the Anchisauria within the Sauropodomorpha. He is one of the classic prosauropods , a term for basal sauropodomorpha outside of the sauropods. Since the prosauropods are not a natural group ( paraphyletic ), the name is rarely used today. An analysis by Yates and colleagues (2010) sees aardonyx as the sister taxon of a clade that contains Melanorosaurus and the sauropods. Representatives of this clade were consistently quadruped. Thus, Aardonyx is the genus most closely related to the sauropods, which was still two-legged (biped). It represents a transition form between the bipedal basal sauropodomorpha and the quadruped sauropod.

Paleobiology

nutrition

Basal sauropodomorphs had narrow, V-shaped jaws and probably fleshy cheeks. Sauropods, on the other hand, show adaptations that allowed the faster ingestion of larger amounts of food ( bulk browsing ): The jaws were wide and U-shaped, which allowed a wider bite, while cheeks were missing. The toothed strips were reinforced on the inside by plates, which helped the teeth to strip off leaves. Aardonyx shows an interesting combination of these features: while the jaws are 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 suspect that the sauropods did not develop in a straight line towards bulk browsing , but that some characteristics emerged independently several times ( homoplasia ).

Locomotion

Features of the limbs of the aardonyx suggest a two-legged gait. The head of the spoke (radius) was egg-shaped, which restricted rotation of this bone around the ulna. Thus, the animal could not pronate (turn inward) the forearm , preventing the palms of the hands from facing down. In addition, the upper arm bone (humerus) made up only 72% of the length of the thigh bone (femur).

However, other features on the arm and leg bones are viewed as adaptations to more quadruple locomotion. For example, the upper end of the ulna shows a craniolateral ridge which, when viewed from above, makes the ulna appear Y-shaped. Such a crest is also found in the quadruped sauropods, but where it is more pronounced. Furthermore, a depression (fossa) in the radius allowed craniolateral movement of the ulna. The hind legs also show some adaptations to quadruple locomotion. The shaft of the femur is straighter, while the fourth trochanter , a bone process serving as a muscle attachment point, is positioned further down (more distally) than in the more basal sauropodomorphs. This allowed the caudofemoralis , the main pulling muscle of the thigh, to have a larger lever arm and thus more strength, but at the same time made it slower. As a result, aardonyx was less rapid than typical basal sauropodomorphs.

Another feature suggesting slower locomotion was the robustness of the first metatarsal bone compared to other basal sauropodomorphs. This indicates that the body weight was not centered on the middle toe ( mesaxonic ), as in basal sauropodomorpha, but that the weight-bearing axis was shifted more towards the middle of the foot ( entaxonic ). This shift also indicates that the legs were a little more splayed outwards than in basal Sauropodomorpha; an adaptation that presumably preceded the obligatory quadruple in evolution. Until now it was assumed that the weight-bearing axis only shifted when the animals were already quadruped. For example, the early sauropod Vulcanodon , although obligately quadruped, shows a mesaxonic foot - a feature that could be interpreted as an evolutionary reversal in the light of the discovery of aardonyx .

Individual evidence

1. ↑ ^{a b c d e f g h i j k} Adam M. Yates, Matthew F. Bonnan, Johann Neveling, Anusuya Chinsamy, Marc G. Blackbeard: A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism. In: Proceedings of the Royal Society. Series B: Biological Sciences. Vol. 277, No. 1682, 2010, ISSN  0950-1193 , pp. 787-794, doi : 10.1098 / rspb.2009.1440 .
2. ↑ ^{a b c d} Adam M. Yates, Matthew F. Bonnan, Johann Neveling, Anusuya Chinsamy, Marc G. Blackbeard: Electronic supplementary information for: A new transitional sauropodomorph dinosaur from the Early Jurassic of South Africa and the evolution of sauropod feeding and quadrupedalism. In: Proceedings of the Royal Society. Series B: Biological Sciences. Vol. 277, No. 1682, 2010, online .
3. ↑ Emese M. Bordy, P. John Hancox, Bruce S. Rubidge: Basin development during the deposition of the Elliot Formation (Late Triassic - Early Jurassic), Karoo Supergroup, South Africa. In: South African Journal of Geology. Vol. 107, No. 3, 2004, ISSN  0371-7208 , pp. 397-412, doi : 10.2113 / 107.3.397 .
4. ^ Adam M. Yates, P. John Hancox, Bruce S. Rubidge: First record of a sauropod dinosaur from the upper Elliot Formation (Early Jurassic) of South Africa. In: South African Journal of Science. Vol. 100, No. 9/10, 2004, ISSN  0038-2353 , pp. 504-506, digital version (PDF; 589.44 kB) .
5. ↑ David B. Weishampel , Paul M. Barrett , Rodolfo Coria , Jean Le Loeuff, Xing Xu , Xijin Zhao , Ashok Sahni, Elizabeth Gomani, Christopher R. Noto: Dinosaur distribution (Late Triassic, Africa). In: David B. Weishampel, Peter Dodson , Halszka Osmólska (eds.): The Dinosauria . 2nd edition. University of California Press, Berkeley CA et al. 2004, ISBN 0-520-24209-2 , pp. 528-529.
6. ↑ Paul Upchurch , Paul M. Barrett, Zhao Xijin, Xu Xing: A re-evaluation of Chinshakiangosaurus chunghoensis Ye vide Dong 1992 (Dinosauria, Sauropodomorpha): implications for cranial evolution in basal sauropod dinosaurs. In: Geological Magazine. Vol. 144, No. 2, 2007, ISSN  0016-7568 , pp. 247-262, doi : 10.1017 / S0016756806003062 .