The species was a small to medium-sized, lightly built, ground-dwelling, bipedal carnivore, that could grow up to 2.2 m (7.2 ft) long and weigh up to 13 kg (29 lb).

[4][5][6] The first fossils of Megapnosaurus were found in 1963 by a group of students from Northlea School on Southcote Farm in Nyamandhlovu, Zimbabwe (then Rhodesia).

Michael A. Raath, the describer, was shown the fossils by school staff in 1964 and over several weeks, was excavated from the Forest Sandstone, the layers dating to the early Jurassic.

[2] The type specimen (QG 1) consisted of a well preserved postcranial skeleton, missing only the skull and cervical vertebrae.

Later in 1968, Raath and D. F. Lovemore discovered additional Jurassic rock layers northeast of the type locality of Southcote Farm.

[5][11] The next year Darlington Munyikwa and Raath described a partial snout of "S." rhodesiensis from the Elliot Formation in South Africa,[12] but the material has been referred to Dracovenator.

[21] Specimen UCMP V128659 was discovered in 1982 and referred to Megapnosaurus kayentakatae by Rowe (1989),[22] as a subadult gracile individual and later, Tykoski (1998)[23] agreed.

kayentakatae because the promaxillary fenestra is absent and the nasal crests are absent; the frontal bones on the skull are not separated by a midline anterior extension of the parietal bones; the anterior astragalar surface is flat; metacarpal I has a reduced distal medial condyle (noted by Ezcurra, 2006); the anterior margin of antorbital fossa is blunt and squared (noted by Carrano et al., 2012); the base of lacrimal vertical ramus width is less than 30% its height (noted by Carrano et al., 2012); the maxillary and dentary tooth rows end posteriorly at the anterior rim of the lacrimal bone (noted by Carrano et al., 2012) Marsh and Rowe (2020) retain the generic name Syntarsus for both QG 1 and MNA V2623, and the respective specimens assigned to these taxa, as opposed to Coelophysis or Megapnosaurus, due to systematic relationships within Coelophysoidea in flux.

In South Africa, several individuals were collected in 1985 from mudstone deposited during the Hettangian stage of the Jurassic period, approximately 201 to 199 million years ago.

[29] In Zimbabwe, twenty-six individuals were collected in 1963, 1968 and 1972 from yellow sandstone deposited during the Hettangian stage of the Jurassic period, approximately 201 to 199 million years ago.

The Forest Sandstone Formation was the paleoenvironment of protosuchid crocodiles, sphenodonts, the dinosaur Massospondylus and indeterminate remains of a prosauropod.

Paul (1988) argued that members of the species lived among desert dunes and oases and hunted juvenile and adult prosauropods.

Paul (1988) suggested that members of the species may have hunted in packs, preying upon "prosauropods" (basal sauropodomorphs) and early lizards.

Fluctuating asymmetry results from developmental disturbances and is more common in populations under stress and can therefore be informative about the quality of conditions a dinosaur lived under.