PSEUDOPATHOLOGIES IN EDMONTOSAURUS ANNECTENS BONES: BIOGENETIC AND DIAGENETIC BONE ALTERATIONS FROM A MONOSPECIFIC BONE BED IN THE LANCE FORMATION, WYOMING

In this study, we report manifestations of bone abnormalities suggestive of post-mortem biogenic and diagenic factors in Edmontosaurus annectens skeletons from a largely monospecific bone bed within the Cretaceous (Maastrichtian) Lance Formation, WY. These types of bone abnormalities are also known as pseudopathologies, due to an appearance that mimics actual disease conditions. It is critical to differentiate pseudopathologies from pathologies, since their misidentification can lead to erroneous conclusions pertaining to diseases and life history. One characteristic of many pseudopathologies is that there is no bone reactivity observable. Pseudopathology is most frequently an indicator of taphonomic processes, environmental conditions and depositional settings. The principal pseudopathologies observed in this largely monospecific bonebed manifest as depressions and bone fractures. The former are hemispherical to elliptical depressions, with opening diameters ranging from approximately 0.5 to 1 cm, and depth varying from shallow (approximately 0.1 cm) to deep (approximately 1 cm). They are found on several elements, such as the pedal phalanx, caudal vertebrae, astragali and ischii. . The arrangement of the depressions on the bone surface varies from isolated to numerous manifestations and with occasional overlapping. From our observations, in combination with literature reports of pseudopathologies and taphonomic processes, we conclude that these depressions are insect borings, thus suggesting insect infestation of surface exposed carcasses prior to fossilization. Early post-mortem fractures frequently observed on ribs, particularly on their distal end, suggest post-mortem ribcage trauma during scavenging. Scavenging is also suggested by several manifestations of tooth traces in other bones. Other erosive modifications to bone texture are indicative of post-mortem weathering, thus strengthening our conclusions that carcasses were exposed prior to burial. However, the uniformly well-preserved bone surface texture in the majority of bones within the bed further indicates that this period of exposure on the ground was relatively brief.