A Late Cretaceous marine long snout “pejelagarto” fish (Lepisosteidae, Lepisosteini) from Múzquiz, Coahuila, northeastern Mexico

•We describe a Mexican Late Cretaceous marine fossil fish, Herreraichthys coahuilaensis, as part of the Lepisisteini that includes the gars.•The only fossil of this species so far known is not well preserved; however we discover enough osteological features that allow us to recognize this as a member of the tribe Lepisisteini, which includes the living gar sor “pejelagartos” and relatives.•This ancient “pejelagarto” fish clearly differs their fossil and extant relatives because it posses an inusual large number of lacrimomaxilla bones and a short premaxilla.•The gars are known as a group of freshwater fish; however H. coahuilaensis was collected in a geological formation entirely deposited under open sea conditions.

Herreraichthys coahuilaensis gen. and sp. nov. is described based on a single specimen collected in the Santonian marls strata of the “Los Temporales” quarry, Coahuila State, northern Mexico. This new species shows the diagnostic characters of the Family Lepisosteidae and tribe Lepisosteini, together with Lepisosteus and Atractosteus. This new fish shows two rows of teeth on dentary and lacrimomaxillae bones, including a lingual row of sharp and small regular size teeth, as well as a medial row of longer and fang-like teeth; this also has a lacrimomaxillary series as the main bite element of the upper jaw and the plicidentine structure on teeth. This Mexican fish differs from the other lepisoestinis in two characters; its lacrimomaxillary series is composed of 32 bones that constitute the largest series as far known among lepisosteiformes, and its premaxilla is comparatively wider and shorter. The occurrence of this specimen into an open marine deposit with no freshwater elements suggests that Herreraichthys was a marine inhabitant; however, there is the possibility that this species was able to temporarily survive in the sea, as Atractosteus spatula does now.