Megapnosaurus, meaning "big dead lizard" in Greek, is an extinct coelophysid theropod dinosaur that thrived approximately 188 million years ago during the early Jurassic Period in present-day Africa. This species was a ground-dwelling, bipedal carnivore of small to medium size, characterized by a light build. It could attain a length of up to 2.2 meters (7.2 feet) and a weight of around 13 kilograms (29 pounds). Initially designated under the genus name Syntarsus, it was later determined to be preoccupied by a beetle, leading to the adoption of the new genus name Megapnosaurus.

Megapnosaurus displayed distinctive features, including an S-shaped neck, elongated hind limbs reminiscent of large bird legs, shorter forelimbs with four digits on each hand (unlike most later theropods), and an elongated tail. Despite its lean physique, Megapnosaurus had a more robust frame compared to other Coelophysoidea members. It was one of the early dinosaurs to be depicted with feathers, although direct evidence supporting this characteristic is lacking.

In a fossil bed in Zimbabwe, the bones of at least 30 Megapnosaurus individuals were discovered together, leading paleontologists to speculate that it may have hunted in packs. Fossils attributed to this species span a considerable time range, encompassing the Hettangian, Sinemurian, and Pliensbachian stages of the Early Jurassic. This suggests the possibility that the fossils represent either a highly successful genus or a group of closely related animals, all presently classified under Coelophysis.