This paper provides the first geological and paleontological data on two Mexican Paleocene fossil localities, the División del Norte and the Belisario Domínguez quarries, recently discovered near Palenque, State of Chiapas. Both are part of the marine outcrops previously known as the Tenejapa (toward the West) and the Lacandón formations (toward the East and in Guatemala). Since the limits of these formations remain unclear in the Palenque area, the geological association of these localities is referred to as the Paleocene Tenejapa-Lacandón Unit. The fossil fishes are particularly abundant and well preserved in these sites; they represent taxa previously known from Eocene localities around the world, whose strata were deposited under continental and marine conditions. This new assemblage is peculiar because it includes potential new species of Pycnodontiformes, Osteoglossiformes, Anguillifromes, Clupeiformes, and "serranids" that might expand their temporal and paleogeografical distribution worldwide and therefore become important elements to understand the evolution of these groups. These 63 my fish localities are the closest, temporally and geographically, sites to the Chicxulub Crater, a crater intimately associated to the Mass Extinction Event at the Cretaceous-Paleogene boundary (K/P). These newly localities represent an important paleontological scenario that will contribute to achieve a better understanding of the marine vertebrate communities throughout this important geological event.

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The Huehuetla quarry is a new fossiliferous site located near the town of the same name, into the region of Sierra Norte, northern Puebla, Mexico. This work represents the formal beginning of paleontological research on this site. This quarry occupies an area of about one hectare that is scarcely exploited with commercial purposes. The rocks rarely extracted in this site are slabs of nice jet-black carbonated shales with microscopic crystals of pyrite; which also are resistant, oily and stinky. The fossils recovered in these slabs belong to different marine vertebrate taxa, which include complete and articulated specimens as well as isolated bones. When it is preserved, the calcium phosphate of these bones is softened and filled with large calcite and pyrite crystals. Taxa represented in Huehuetla quarry constitute a peculiar assemblage that includes Nursallia aff. tethysensis, Tselfatia formosa, Goulmimichthys roberti, Hastichthys, indeterminate species of Enchodus and Clupeidae, as well as an indeterminate mosasaur. This is the first report of the pycnodontid N. tethysensis and of the dercetid Hastichthys fish all over America. This work provides evidence supporting the taxonomical validity of the species G. roberti. Based on its fossil content and lithology, it is determined that the fossil bearing strata of the Huehuetla quarry are part of the Turonian marine deposits of the Agua Nueva Formation.

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