Tahnaichthys magnuserrata gen. and sp. nov., a double-hump pycnodontid (Actinopterygii, Pycnodontiformes) fish from the Albian limestones of the Tlayúa Quarry, Puebla, Mexico

Abstract

Tahnaichthys magnuserrata gen. and sp. nov. is described here based on three well-preserved Albian specimens recovered in the lagoon-coastal deposits of the Tlayúa Quarry, Puebla, Mexico. This species belongs to the order Pycnodontiformes and shows the diagnostic features of the family Pycnodontidae, including the presence of a posterior parietal process distally branched, toothless reniform maxilla, anterior thin wings at the base of the haemal and neural spines, and slender dentary with two teeth. In addition, this species shows unique features never observed before in other pycnodontids as the presence of two unequal predorsal humps or prominences, including a slight hump just behind the occiput and a large hump rising in front of the dorsal fin. The predorsal scutes are thick, have a longitudinal row of unequal spines, and show thin lateral wings projected ventrally, covering a large part of the predorsal trunk region. In the new species, the modified bar-like scales of the predorsal region have tiny posterior wings ornamented with tubercles scattered or arranged in dorsoventral short ridges. In addition, the premaxilla of this new species is ventrally broad and has a large single incisiform tooth opposing two small, oval dentary teeth. This new species exhibits a peculiar mixture of osteological features that, for the moment, complicate its taxonomic designation at the suprageneric level (subfamily or tribe). Although this is the second pycnodontiform species from Tlayúa formally described, the present discovery increases the taxonomic diversity of the pycnodontids in North America and the Paleogulf of Mexico domain.