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.
Vinctifer ferrusquiai sp. nov. is described in this paper. This aspidorhynchid fish was found in Kimmeridgian marine deposits of the Sabinal Formation, exposed in the Llano Yosobé, near Tlaxiaco, Oaxaca, Mexico. The single specimen of this species shows enough diagnostic characters to be included in the order Aspidorhynchiformes, the family Aspidorhynchidae, and the genus Vinctifer. These characters include an elongate rostrum consisting of the premaxillae fused and anteriorly elongated, forming a tube-like, as well as an preopercular sensory canal located close to the posterior edge of the preopercle. Other features are the lack of premaxilla, the development of a wide posterior expansion of the maxilla, and a stout triangular preopercle. A unique combination of characters supports the erection of this new species, whose ganoine on dermal bones of the head are strongly ornamented with tubercles and ridges, and the flank scales are entirely smooth and not serrated. This Jurassic record is the first indubitable pre-Cretaceous finding of Vinctifer, the oldest into the Hispanic Corridor, and the oldest in North America.
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