Recent fieldwork in the Early Tithonian of northeastern Mexico has yielded the partial cranium and associated fragmentary postcranial elements of a thalattosuchian. The specimen is described and referred to a new species of the genus Geosaurus characterised by elongated, narrow, oval supratemporal fenestrae, and a prefrontal that excludes the frontal from the centre of the dorsal margin of the orbits; the cranium is gracile and was probably more longirostrine than occurs in other members of this genus. The new taxon represents the second occurrence of the genus Geosaurus in the Mexican Gulf and is in agreement with the partial isolation of the area during the Late Jurassic, which was previously suggested by the microfossil and invertebrate assemblages. To cite this article: M.-C. Buchy et al., C. R. Palevol 5 (2006).