IN VIVO DINOSAUR BONE FRACTURES WITH BEHAVIORAL IMPLICATIONS

MALCOLM BEDELL; BRUCE ROTHSCHILD; DÍAZ-MARTÍNEZ, IGNACIO; PENÉLOPE CRUZADO CABALLERO

Congreso; 1st Palaeontological Virtual Congress; 2018

Bone Fractures are uncommon in the Mesozoic dinosaurian record but, when present, provide unique insights to ancient behavior. Fractures were macroscopically examined as to type within the dinosaurian fossil record of major museum fossil collections in order to provide insight as to their derivation and behavioral implications.Such fractures can be classified as related to a single traumatic event or to repetitive stresses. Those related to a single traumatic event include: 1) Full fractures, with loss of continuity,which may result in either loss of the distal portion or a pseudo-arthrosis. 2) Partial fractures involving full or partial detachment of a bone fragment. These are divided into chip and pilon fractures, defined by joint margin and diaphyseal location (e.g. the metatarsal fracture in ornithomimid SMP VP-971), respectively. 3) Greenstick fractures, which are incomplete, resulting in exostoses in juvenile individuals (e.g. some metapodials of Apatosaurus Tate-001). 4) Impact fractures, wherein one bone penetrates another, resulting in traumatic subsidence (e.g. the pedal fractures in a basal ornithischian YPM 5819 and 5875). These are distinguishable from avascular necrosis or osteochondritis because the latter only localize to vascular watershed regions (areas of bone with a single arterial source, blockage of which results in bone death). Fractures attributable to repetitive stress include:1) Fatigue fractures due to biomechanical responses to repetitive stresses which exceed the elastic modulus of normal bone.2) Insufficiency fractures involving failure of abnormal bone. The result of either is production of microfractures and cleft formation. Thus, the presence and character of fractures can provide unique insights into Mesozoic dinosaurian behaviour. From speed to predator-avoidance, defensive and offensive use of feet, and repetitive behavior as involved in migration, specific fracture pattern and character allow an otherwise unknowable understanding of Mesozoic vertebrate behavior.