Paleobiology and Taphonomy of the pycnodont fish Nursallia gutturosum, based on material from the Latest-Cenomanian-Middle Turonian Vallecillo platy limestone, Mexico

The platy limestone deposit of Vallecillo, located in north-eastern Mexico, offers a wide variety of invertebrate and vertebrate species dated to the latest Cenomanian-middle Turonian (Late Cretaceous). The deposit is known to contain well preserved fossils, e.g., fishes, in which the bones are recrystallized to calcite but soft tissue is also preserved. The fish assemblage is dominated by pelagic fast swimmers but also includes the common pycnodont Nursallia gutturosum, a discus-like and compressed fish that was likely well-suited for maneuverability. A review of 90 individuals of this taxon indicates the presence of different ontogenetic stages, from early young to old age. The size range distribution of individuals also suggests intermittent migration out of the Vallecillo area. The taphonomical decay analysis of N. gutturosum allows for a differentiation of five preservational stages. The presence of frequently complete and articulated specimens suggests a deep dwelling life style, without carcass flotation to the surface.