|Illustration of a fossil of Iliosuchus|
The only known fossils of this genus are three ilia (BMNH R83, OUM J29780 and OUM J28971) from Stonesfield Slate, Oxfordshire, England. From the holotype BMNH R83, Friedrich von Huene described and named the only species, I. incognitus, in 1932. The generic name is derived from the ilium and Greek Souchos, the crocodile god. The specific name means "unknown" in Latin. Another species, I. clevelandi, was proposed in 1976 by Peter Galton, who assigned Stokesosaurus clevelandi to Iliosuchus, but this has not been followed.
The Iliosuchus ilia, very small with a length of nine to ten centimetres, have a vertical supra–acetabular ridge on the surface, similar to tyrannosaurids and many other predatory dinosaurs belonging to the group Tetanurae, including Piatnitzkysaurus and Megalosaurus. Such fargmentary and incomplete material is inadequate for accurate classification; nonetheless, Iliosuchus has sometimes been considered a tyrannosaurid ancestor. This is unlikely to be correct as the bones cannot be distinguished from small individuals of Megalosaurus, a megalosaurid. Whatever the case, Iliosuchus is not diagnostic and is therefore dubious. If Iliosuchus incognitus is a tyrannosauroid, it would be a possible ancestor to Proceratosaurus, the earliest recognized tyrannosauroid, and would be the earliest of the tyrannosauroid family tree.