[1] Eohyosaurus is known solely from the holotype SAM-PK-K10159, a partial skull missing the front end, with associated incomplete lower jaws currently housed at the Iziko South African Museum, Cape Town.

The specimen was discovered by Frederik Petrus Wolvaardt in December 2000, loose on boulder-strewn slopes at the base of a cliff, at Farm Lemoenfontein 44, Rouxville District of the Free State Province.

Such traits include the presence of a sagittal crest on parietal bone, maxillae and dentaries that are expanded from the middle to the sides, and with teeth present on both the occlusal and lingual surfaces.

Unlike rhynchosaurids that possess a short anguli oris crest on the jugal, in Eohyosaurus it is present on the side surface of the maxilla, while Mesosuchus lacks it entirely and it is unknown in Howesia.

As in Howesia but not Mesosuchus and most rhynchosaurids (where it contacts the quadratojugal), the back portion of its jugal is short and ends at approximately 50% of the front-to-back length of the infratemporal fenestra.