Neogene crocodylians from the Central Great Plains: spatiotemporal histories and relationships with regional climatic and environmental changes

Abstract

ABSTRACT Crocodylian fossils are well documented from Upper Cretaceous and lower to middle Paleogene deposits in the mid-high latitudes of the Western Interior, whereas the only extant North American taxon, Alligator mississippiensis, is restricted to the lower-latitude wetlands of the southeastern United States. The departure of crocodylians from the Western Interior has been inferred to represent a major shift from more equable, warmer, wetter climates in the Paleogene to more seasonal, cooler, drier climates in the Neogene. The timing of further geographic range shifts during the Neogene, including the local extinction (extirpation) of crocodylians from the Great Plains, is poorly constrained. We document the Neogene crocodylian fossil record of the Central Great Plains (CGP) in order to constrain the timing of mid-continental crocodylian extinctions against a backdrop of climatic and environmental changes. The Neogene CGP crocodylian fossil record consists of mostly incomplete specimens, likely referable to the extant genus Alligator, and appears to document multiple latitudinal range shifts that are spatiotemporally consistent with regional climatic and environmental changes inferred from independent proxy evidence. The last appearance datum (LAD) for crocodylians in the CGP is ∼6 Ma, which suggests that climatic and environmental conditions in the region were unfavorable to crocodylians after this time. In general, Neogene crocodylian fossils throughout the Great Plains are not abundant. Barring taphonomic biases or sampling issues, this could imply low population densities, and/or that the fossil-bearing areas in this region were close to the northernmost limits of crocodylian (cf. Alligator) distributions during the Neogene.