Semionotiformes is a diverse extinct group in Neopterygii. It is well represented in the Mesozoic, occurring in marine and continental strata worldwide. However, some diagnostic characters of Semionotiformes and, in particular, of Semionotidae, have been under debate, due to the description of new taxa or revision of previously known ones. In this paper, we provide a detailed description of the first unequivocal record of Semionotidae from Gondwana, i.e., Lophionotus parnaibensis, sp. nov. from the Pastos Bons Formation, Upper Jurassic, in the Parnaíba Basin, northeastern Brazil. It was included in the genus Lophionotus mainly due to the presence of smooth cranial bones, triangular lateral expansion of antorbital portion of frontal, and ratio length/width of frontals lower than three times. It was recovered as a new species due to a unique combination of characters. This discovery represents the most recent occurrence of the genus, which was previously recorded only in the U.S.A. up to the Early Jurassic.