New eggshell of ratite morphotype with predation marks from the Eocene of Colorado

Abstract

ABSTRACT A large number of eggshell fragments from a single locality of the lower Eocene (?Wa5-Wa6 biochron) DeBeque Formation of northwestern Colorado are interpreted as representing a single, disintegrated avian egg. These eggshells, and eggshells from two other localities within the formation, are of the ratite morphotype within the ornithoid basic type. They are unlike any previously described eggs and are assigned to Incognitoolithus ramotubulus oogen. et oosp. nov. This oospecies is distinguished by its smooth outer surface, assumed ellipsoidal shape, relatively large size, relatively thick eggshell, and presence of both non-branching and branching pore canals. Pore openings are clustered in grooves and pits on the outer surface, exhibiting the “aepyornithid” pore pattern. The eggshell fragments preserve a number of holes that were produced by impact from the outside. These marks are thought to have been produced by a predator, most likely avian. Fractures on many of the eggshell fragments occur on the inner surface but do not extend to the outer surface. These fractures are thought to be the result of lithostatic pressure following burial.