First report of the genus Thorectichthys (Ellimmichthyiformes) in America, from the Cenomanian deposits of the Cintalapa Formation, Chiapas, southeastern Mexico.

The El Chango quarry is an outstanding paleontological site of Mexico. The marine limestones of this site represent a small outcrop of the Cintalapa Formation and bear a significant assemblage of Early Cenomanian continental plants plus marine crustaceans, decapods, mollusks, and fishes. This paper includes the description of a double-armored herring species from El Chango, which is named Thorectichthys fideli and belongs to the family Paraclupeidae, in the order Ellimmichthyiformes. This new species shares the diagnostic generic features with T. marocensis and T. rhadinus , two slightly younger North African species previously discovered in Cenomanian–Turonian deposits of the Akrabou Formation, Morocco. The new species has a couple of peculiar features never before observed in the ellimmichthyiforms; the caudal skeleton of this fish has four uroneurals, and the horizontal limb of the preopercle is dorsally notched allowing the superficial lateral exposure of a broad and massive posterior process of the quadrate. Including this species in a comprehensive phylogenetic analysis confirms the monophyletic nature of Thorectichthys and its inclusion as a basal clade of the family Paraclupeidae. Thorectichthys fideli sp. nov. adds to an increasing assemblage of Mexican Cretaceous ellimmichthyiforms that includes ancestral as well as more derivatives species that shows the broad Albian–Cenomanian distribution of the ellimmichthyiforms, along the epicontinental environments of the Tethys Sea. • First record of Thorectichthys from Early Cenomanian outcrop in America, the third species of and oldest one. • Phylogenetic analysis recovery to Thorectichthys as a monophyletic genus. • Their discovery reinforces the link between Morocco and the Cintalapa Formation faunas. [ABSTRACT FROM AUTHOR]