Antetonitrus

Antetonitrus
Antetonitrus ingenipes , fossils
Temporal occurrence
Upper Triassic ( Norium )
228 to 208.5 million years
Locations
Orange Free State , South Africa (Lower Elliot Formation )
Systematics
Dinosaur (dinosauria) Lizard dinosaur (Saurischia) Sauropodomorpha Sauropods (Sauropoda) Antetonitrus
Scientific name
Antetonitrus
Yates & Kitching , 2003
Art
Antetonitrus ingenipes

Antetonitrus is a genus of sauropod dinosaur from the Upper Triassic of South Africa . The only species is Antetonitrus ingenipes . As one of the earliest and most original known sauropods, this genus sheds light on the still little-known origin of this group. Unlike its two-legged forerunners, Antetonitrus already walked four-legged like all other sauropods. The hand showed a flexible thumb; the front extremity was consequently not used exclusively for locomotion, as was the case with other sauropods, but presumably also assumed a gripping function.

The name Antetonitrus ("before the thunder", Latin ante - "before"; tonitrus - "thunder") indicates the very early appearance of this sauropod, long before Brontosaurus (" thunder lizard ") appeared on the scene. The second part of the species name, ingenipes (Latin ingens - "massive"; pes - "foot") indicates the robust hands and feet.

features

This small, stocky sauropod is estimated to be 8 to 10 meters long and 1.5 to 2 meters high at the waist. Compared to more primitive Sauropodomorpha such as Plateosaurus , the front extremity was greatly elongated while the metatarsus was shortened. Antetonitrus thus already showed the appearance typical of all sauropods with approximately the same length of fore and hind limbs.

The obligatory two-legged Plateosaurus could not turn its hands palm down ( pronate ); instead, the palms of the hands were facing each other, the hand probably served as a gripping tool in this genus. In contrast, Antetonitrus could pronate his hands, which is what makes effective four-legged locomotion possible. In later sauropods, pronation was forced and the palms could no longer be turned outwards ( supinated ). The rounded lower end of the spoke in Antetonitrus suggests that the rolling motion of the spoke necessary for supination was possible in Antetonitrus . The thus movable forearm could have enabled the front extremity to have a gripping function in addition to its locomotion function. This is also suggested by the flexible thumb and large extensions in the upper and lower arm (the large deltopectoral ridge and the olecranon ) that serve as muscle attachment points .

As with later sauropods, the metatarsus was shortened. The hand and foot were robust, while the femur showed the typical oval cross-section; both are adaptations to the increasing body size. The enlarged claw of the first toe was longer than metatarsal I, as in other sauropods; but this claw did not yet show the sickle shape typical of sauropods. The thigh bone was not straight, as in other sauropods, but rather curved slightly S-shaped when viewed from the side. The vertebrae of Antetonitrus are characterized by high spinous processes and strongly pronounced hyposphere-hypantrum joints , additional connecting elements that give the spine stability.

Systematics

Cladogram , simplified from Yates and Kitching, 2003:
Sauropoda    Anchisaurus        Melanorosaurus        Antetonitrus        Isanosaurus        Kotasaurus        Vulcanodon   Eusauropoda    Shunosaurus        Barapasaurus        Omeisaurus      Neosauropoda
Systematic position of antetonitrus

Antetonitrus is considered to be one of the most original known sauropods. The relationship to other very original sauropods, such as Blikanasaurus , Melanorosaurus, and Isanosaurus , is unclear because of the sparse fossil record. Presumably these genera were more original than Vulcanodon and Kotasaurus .

Finds

So far, two specimens have been described that James Kitching discovered in 1981 in the South African province of Orange Free State . They come from the Lower Elliot Formation , which is dated to the Norium . The Lower Elliot Formation is of great importance for its rich fossil fauna; The remains of two other very early sauropods, Melanorosaurus and Blikanasaurus , also come from these layers .

The finds were originally attributed to a prosauropod ( Euskelosaurus sp.) By Kitching and Raath (1984) . The holotype specimen mainly includes fore and hind limbs as well as a few vertebrae and a pubic bone , the second specimen includes parts of the forelimbs. The holotype specimen is a not yet fully grown animal, which is indicated by the vertebral arches that have not yet grown together with the vertebral bodies. The second specimen was 80% smaller than the holotype. Both finds are archived in the Bernard Price Institute for Palaeontological Research in Johannesburg .

Individual evidence

1. ↑ ^{a b c d e f g h i} Adam M. Yates, James W. Kitching: The earliest known sauropod dinosaur and the first steps towards sauropod locomotion. In: Proceedings of the Royal Society of London. Series B: Biological Sciences. Vol. 270, No. 1525, 2003, ISSN  0080-4649 , pp. 1753-1758, doi : 10.1098 / rspb.2003.2417 .
2. ^ Heinrich Mallison: The digital Plateosaurus II: An assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount. In: Acta Palaeontologica Polonica. Vol. 55, No. 3, 2010, ISSN  0567-7920 , pp. 433-458, doi : 10.4202 / app.2009.0075 .
3. ↑ Jeffrey A. Wilson: Overview of Sauropod Phylogeny and Evolution. In: Kristina Curry Rogers, Jeffrey A. Wilson (Eds.): The Sauropods: Evolution and Paleobiology. University of California Press, Berkeley CA et al. 2005, ISBN 0-520-24623-3 , pp. 23-26.
4. ↑ John Pickrell: New Dino Species Found on Dusty Shelf. In: National Geographic News. July 10, 2003, accessed August 11, 2014 .