Megaconus mammaliaformis is preserved as a slab (left) and a counter-slab (right) of shale deposited in a shallow lake. The preserved part of the skeleton, from head to rump, is about 21 cm (8 inches). By the length of long bones, Megaconus is estimated to weigh about 250 grams (almost 9 ounces). The fossil assemblage from the Daohugou Site include several other mammals, such as semi-aquatic swimmer Castorocauda, gliding mammal Volaticotherium, feathered dinosaurs, amphibians, abundant arthropods and plants. Megaconus is the first skeletal fossil of a mammaliaform group otherwise only known by their teeth, but show a long history extending back to Late Triassic, and a wide distribution in the Jurassic.