Dino of the Week: Antetonitrus

an artist's depiction of two Antetonitrus

Type Species: Antetonitrus ingenipes

Classification: Dinosauria - Saurischia - Sauropoda

Time Period: Late Triassic to Early Jurassic

Location: South Africa

Diet: Herbivore

Antetonitrus lived between the Late Triassic and Early Jurassic, one of the few dinosaurs to cross the Triassic-Jurassic boundary. It’s known by one specimen found in the Elliot Formation of South Africa, which records the Triassic-Jurassic boundary in southern Africa. Antetonitrus lived alongside the far more common Massospondylus, also found at the Elliot Formation. Other creatures from Antetonitrus’ habitat include several early ornithischians (bird-hipped dinosaurs) and lots of crocodylomorphs, along with crustaceans, fishes, and turtles. 

Antetonitrus is one of the oldest known sauropods, and it’s remarkable in that it possesses characteristics both of prosauropods and sauropods; because of this, scientists have poured over its remains to decipher clues about sauropod evolution in the Late Triassic. The specimen discovered measured up to thirty feet in length and stood six feet tall at the hips, but because the vertebral neural arches weren’t fused, the remains likely belong to a juvenile so that adults would’ve been much larger. Unlike prosauropods, Antetonitrus was primarily quadrupedal, and its forelimbs were much longer relative to its hind legs than seen with earlier sauropodomorphs. Yet Antetonitrus retained prosauropod characteristics: the first digit of its hand – the thumb – was twisted and flexible, enabling Antetonitrus to use it for grasping. Derived sauropods weren’t able to grasp, and their wrists had thick, robust wrist bones arranged in a manner that locked the hand into a permanent pronated position, which enabled the hands to bear the weight of the limbs. Antetonitrus’ wrist bones were broader and thicker than seen in prosauropods, but it had yet to reach the permanent pronated position of sauropods. Derived sauropods had a sickle-shaped claw on the first toe of their hind feet, and while Antetonitrus had a claw, it wasn’t sickle-shaped. Its femur was slightly S-curved (sigmoidal) in the lateral view, whereas saurppods had straight femurs. This ‘mixed bag’ puts Antetonitrus in the odd stage between strict prosauropods and sauropods.