A new species of Heckelichthys from the Muhi Quarry (Albian-Cenomanian) of central Mexico

A new species of ichthyodectiform is presented here. The study is based on 36 fish specimens recovered from the Muhi Quarry, a mid-Cretaceous (Albian-Cenomanian) Fossil-Lagerstätte in Hidalgo, central Mexico. This Mexican taxon is identified as a new species of Heckelichthys due to: presence of an elongated head, second infraorbital being the longest, small teeth, articulation of mandible with the skull anterior to the orbit, small opercle, and ventral arm of the preopercle longer than the dorsal arm. Additionally, Heckelichthys preopercularis sp. nov., differs from the previous known species of Heckelichthys, H. vexillifer and Heckelichthys sp. (Vallecillo) because it exhibits some unique characteristics in the preopercle, including: posteroventral portion of ventral arm long, extending to the level of the posterior edge of the opercle, and dorsal arm short and narrow from its base. Likewise, in the phylogenetic analysis performed here, Heckelichthys preopercularis sp. nov. is placed in the monophyletic group of Heckelichthys, this clade being a derived group of the Cretaceous ichthyodectiforms. Heckelichthys preopercularis sp. nov. shows closer phylogenetic affinities with Heckelichthys vexillifer; this relationship is supported by one synapomorphy, dorsal limb of preopercle short, reaching to level of middle height of opercle. The occurrence of Heckelichthys preopercularis sp. nov. in the Muhi Quarry expands the diversity and distribution of the genus in the western part of the Tethys Sea, and represents the oldest record of the genus in the world.