A New Regurgitalite from the Early Eocene of Wyoming (USA) Provides Evidence for Predation on “Armored” Glyptosaurid Lizards and Diurnal Behavior of Early Owls

Bromalites (trace fossils produced by food processing) from the early Eocene Willwood Formation of Wyoming contain abundant glyptosaurid lizard skeletal elements. They clearly represent bromalites as they are discrete, three-dimensional, disarticulated accumulations of biological materials. Furthermore, they contain abundant skeletal elements, principally osteoderms, that exhibit no indication of digestion, so they can be identified as regurgitalites. The Willwood specimens represent orniothoregurgitalites, specifically strigilites, the regurgitalites of owls. These strigilites are assigned to Sauresus osteodermus igen. et isp. nov. This ichnotaxon is characterized by an elongate, sub-cylindrical or sub-ovoid bromalite pellet with irregular surface texture that is composed of a micritic matrix and contains abundant, well-preserved skeletal elements of glyptosaurids, principally osteoderms. The strigilites were probably produced by Primoptynx poliotauros that used its feet to kill glyptosaurids. The lizard, rather than rodent, content of the strigilite supports the hypothesis that Eocene owls were diurnal in habit and only became nocturnal in the Oligocene.