Antetonitrus is a genus of sauropod dinosaurs that inhabited South Africa during the Upper Triassic. Its only species is Antetonitrus ingenipes. As one of the earliest known genera of sauropods, Antetonitre sheds light on the as yet poorly understood origins of this group of dinosaurs.
Unlike the bipedal forms that preceded it, it already moved on 4 legs, like other sauropods. His hand had a flexible thumb; therefore, the forelimbs were used not only for locomotion, as in other sauropods, but, presumably, they also performed a grasping function.
The generic name “Antetonitrus”, which can be roughly translated from Latin as “pre-thunder” or “thunder harbinger” (ante = before; tonitrus = thunder), indicates a very early appearance of this genus of sauropod dinosaurs, which occurred long before the appearance of the brontosaurus (Brontosaurus) (“thunder lizard”). The specific name “ingenipes” (lat. ingens = massive; pes = foot) emphasizes that this species had powerful fore and hind limbs.
This relatively small, stocky sauropod is estimated to have been 8 to 10 meters long and 1.5 to 2 meters tall at hip level. Compared to earlier sauropodomorphs such as Plateosaurus, the antetonitre’s forelimbs were greatly elongated, while the metatarsus was shortened. Thus, he already had a typical appearance for all sauropods with approximately equal length fore and hind limbs.
The bipedal Plateosaurus could not turn the hands with the back down, without which effective movement on 4 legs is impossible; his hands were facing each other and presumably performed a grasping function. However, the rounded lower end of the antetonite’s radius suggests that it may have rotated it outwards.
Due to this, the forearm, which was mobile, could provide additional grasping function of the forelimbs. Flexible thumbs, as well as large processes of the shoulder and forearm (large pectoral crest and olecranon) that serve as a place of attachment for muscles, are also pushing to this conclusion.
Like later sauropods, the metatarsus of the antetonite was shortened. The hand and foot were massive, while the femur had a typical oval cross-section; both of these traits served as a means of adaptation to increasing body size.
The enlarged first toe claw was longer than the first metatarsal, as in other sauropods; however, it did not yet have the crescent shape typical of them. The femur was not straight, as in other sauropods, but had a slight S-curve in lateral view. Antetonite vertebrae were distinguished by high spinous processes and strongly pronounced hyposthene-hypantrum articulations, which gave the dinosaur spine additional strength.
Antetonitere is considered one of the earliest genera of sauropods. However, its relationship to other very early sauropod genera, such as Blikanasaurus (Blikanasaurus), Melanorosaurus (Melanorosaurus) and Isanosaurus (Isanosaurus), has not been elucidated due to insufficient information about its skeletal remains. It is assumed that these genera were earlier than Vulcanodon and Kotasaurus (Kotasaurus).
So far, only 2 specimens of antetonite have been described, discovered by James Kitching in the South African province of the Orange Free State (now the province of the Free State). Both are found in the lower layer of the Elliot Formation, which is the same age as the Norian. The lower layer of the Elliot Formation is very rich in fossils; it also contained fossils of two more very early genera of sauropods, Melanosaurus and Blycanasaurus.
The found remains were originally attributed by Kitching and Raat to the genus Euskelosaurus (Euskelosaurus sp.) prosauropod subgroups. The holotypic copy of the antetoniter includes mainly the front and hind limbs, as well as several vertebrae and pubic bone, and the second copy is part of the front limbs.
At the same time, the holotypic copy belongs to the young animal, as evidenced by the vertebral arches that have not yet fused with the bodies of the vertebrae. The second copy is 80 % less than the roof. Both of these findings are stored in the archive of the Institute of Paleontological Research of Bernard Price in Johannesburg.
