Gars (Lepisosteidae) are ray-finned fishes with controversial relationships to other actinopterygian lineages. When fossil taxa are considered, gars are grouped with Mesozoic macrosemiids and 'semionotids' in the Semionotiformes, but the intra-relationships within this order are still elusive. Here, the evolutionary history of gars is reinvestigated using a set of well-preserved extinct semionotiform taxa in a phylogenetic analysis. Results indicate that the gar lineage roots in a clade of Late Jurassic-Cretaceous semionotiform fishes. The closest relatives to gars were plant-eating and detritivorous freshwater fishes. The occurrence of semionotiform remains in Early and early Late Cretaceous continental deposits worldwide possibly reflects an important radiation of this group, comparable to the present-day diversification of cypriniforms. Other Late Triassic to Early Cretaceous semionotiform taxa are gathered in a single clade with weakly supported internal nodes, pointing out the necessity to better understand the osteology of these fishes.