Lewisuchus admixtus is an archosaur relative of dinosaurs related to Marasuchus and Pseudolagosuchus. It comes from the late Triassic Los Chanares fauna of La Rioja, Argentina. Of the original material assigned to this animal, the astragalus and pes belong to a smaller proterochampsid, and the femur belongs to Lagosuchus. The braincase, partial mandible , maxilla with teeth and postcrania remain as Lewisuchus, which may trun out to be the same as Pseudolagosuchus.
Allosaurus was a powerful predator that walked on two powerful legs, had a strong, S-shaped neck, and had vertebrae that were different from those of other dinosaurs (hence its name, the "different lizard"). It had a massive tail, a bulky body, and heavy bones. Its arms were short and had three-fingered hands with sharp claws that were up to 6 inches (15 cm) long.
Allosaurus was up to 38 feet long (12 m) and 16.5 feet tall (5 m). It weighed about 1400 kg. It had a 3 feet long (90 cm) skull with two short brow-horns and bony knobs and ridges above its eyes and on the top of the head. It had large, powerful jaws with long, sharp, serrated teeth 2 to 4 inches (5 to 10 cm) long.
Gastralia (hanging belly ribs) are thin, fragile ribs that helped support and protect the internal organs (like the lungs) in the middle area of the body. These ribs were not attached to the backbone; they were attached to the skin in the belly area.