Paleobiology of hesperornithiforms (Aves) from the Campanian Western Interior Seaway of North America, with analyses of extant penguin bone histology

Cretaceous marine hesperornithiform birds are assumed to have been piscivorous based on jaw morphology, the presence of small, recurved teeth, and the association of a Kansas Baptornis advenus specimen with coprolites containing fish remains. Other evidence for the diet of these flightless birds is lacking, but now the preservation of teeth with a new Hesperornis specimen from Devon Island, Nunavut, in the Canadian Arctic has prompted the first dental microwear analysis of these birds. Pit and scratch patterns in the enamel indicate that this high latitude seabird may have eaten soft-­‐bodied crustaceans and/or mollusks, such as cephalopods, prior to death, rather than relying heavily on fish. The incorporation of organisms other than fish in the Hesperornis diet is in agreement with the paucity of small-­‐ and medium-­‐sized fish fossils found in Campanian high latitude environments. Osteohistological analysis of the femur of this specimen indicates that it was a sub-­‐adult bird. While changes in diet through ontogeny are common in many modern seabirds, the late sub-­‐adult ontogenetic stage of this Devon Island Hesperornis suggests that the presumed consumption of crustaceans and/or mollusks was not specifically associated with a specialized nestling or juvenile diet. These analyses provide the first direct evidence of feeding behavior in hesperornithiforms in polar environments, and suggest that their diet may have been more variable than previously assumed. Given their broad North American geographical distribution, the ecology of these birds likely varied along a latitudinal gradient, and strong seasonality in Campanian high latitude ecosystems may have given rise to differences between high and mid latitude food webs.