Mesosuchus is an extinct genus of basal rhynchosaur from middle Triassic (Anisian stage) deposits of Eastern Cape, South Africa. It is known from the holotype SAM 5882, a partial skeleton, and from the paratypes SAM 6046, SAM 6536, SAM 7416 and SAM 7701 from the Aliwal North Euparkeria site. It was found in the Burgersdorp Formation of the Beaufort Group (Karoo Basin) and referred to the middle Cynognathus Assemblage Zone. It was first named by David Meredith Seares Watson in 1912 and the type species is Mesosuchus browni.

 Mesosuchus browni (Watson 1912) Early Triassic ~240 mya, ~40cm in length, was found in a sandstone block along with Euparkeria, hence the name, Mesosuchus, which indicates an affinity with crocodilians. Further excavation revealed the two skeletons (Broom 1913a,b) and the relationship of Mesosuchus to rhynchosaurs. Romer (1956) considered rhynchosaurs and sphenodontians to be related, but Benton (1985) and Carroll (1988) mistakenly split them apart by placing too much emphasis on the lack of fusion in the teeth and tarsus rather than considering the suite of characters that more parimoniously unites them. Mesosuchus was derived from a sister to the sphenodontian, Brachyrhinodon and the trilophosaur, Trilophosaurus. Mesosuchus phylogenetically preceded Hyperodapedon and the rest of the Rhynchosauria.

 Distinct from Brachyrhinodon, the skull of Mesosuchus had distinct teeth not fused to the skull bones. The nares were joined without a central premaxilla bone dividing them. The temporal bars were more gracile with larger temporal openings. The jugal was more gracile. The quadrant leaned anteriorly. The premaxilla extended down further.

 The cervicals were longer and taller. The vertebral spines were taller.

 The scapulocoracoid was larger. The manus was smaller.

 The pelvis had deeper ventral elements and a broad pubic apron. The tarsal elements were not fused together.

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