A new genus of ionoscopiform fish (Halecomorphi) from the Lower Cretaceous (Albian) lithographic limestones of the Tlayua quarry, Puebla, Mexico

Quetzalichthys perrilliatae n. gen. and sp. is described based on five specimens from Lower Cretaceous (Middle-Upper Albian) limestones of the Tlayua Quarry, near Tepexi de Rodriguez, Puebla, Mexico. This new taxon displays the diagnostic characters of lonoscopiformes, which consequently designate it as a new member of this order of Mesozoic fishes. Additionally, Quetzalichthys n. gen. shares several derived characters with Ionoscopus and Oshunia, including the presence of more than 15 supraneurals, solid and well-ossified monospondylous vertebrae with two lateral longitudinal oval fossae, thin scales of the amioid type, and the ventral surface of some circumorbital bones being intensely pitted. Quetzalichthys perrilliatae is characterized by three unique characters: 26 abdominal centra, 21 principal dorsal fin rays, and two supraorbitals. Additionally, its unpaired fins and tail show conditions intermediate to those found in Ionoscopus and Oshunia. A cladistic analysis, of lonoscopiformes, including both taxa found in the Tlayua Quarry (Quetzalichthys and Teoichthys), identifies two monophyletic families within the order, Ophiopsidae (including Ophiopsis, Macrepistius, Teoichthys) and Ionoscopidae (involving Ionoscopus, Oshunia, and Quetzalichthys).