New Mexico Geological Society Annual Spring Meeting — Abstracts

A nearly complete skull of a chasmosaurine ceratopsian dinosaur from the upper Campanian Kirtland Formation (Farmington Sandstone Member) of northwestern New Mexico shows evidence of an attack by a large tyrannosaurid dinosaur. The right maxilla, the right epijugal, the right squamosal, and the left premaxilla exhibit extensive trauma in the form of several bite marks (dentalites). The bite marks on the right maxilla, the right squamosal, and the left premaxilla are full penetrations, whereas those on the epijugal are partial penetrations. Some of the largest bite marks are located on the left premaxilla and are approximately 6 cm long. Furthermore, the orientation of the bite marks indicates the angle of inclanation of the head of the tyrannosaurid during biting. The bite marks on the right side of the skull, especially those on the maxilla, record two events. During one of the events, the tyrannosaurid kept its head at a 70° angle relative to the ceratopsian head and attacked it from the side. The second event shows the tyrannosaurid facing the ceratopsian and biting it along the long axis of the maxilla. The bite marks on the left premaxilla show the position of the tyrannosaurid head at a 70° angle in relation to the ceratopsian head. The bone surface around the largest bite mark on the right maxilla has smooth margins that demonstrate that the ceratopsian survided the attack by the tyrannosaurid. However, the lack of bone remodeling around other identified bite marks suggests that most of the biting likely occurred postmortem or resulted from a dealy attack that killed the ceratopsian. Furthermore, based on the position of the bite marks and their accumulation on both sides of the ceratopsian skull, the tyrannosaurid attacked from the right and the left sides. This specimen adds new documentation of active predation by a tyrannosaurid dinosaur and thus runs contrary to the idea that tyrannosaurids were scavengers.