Plesiosaur spinal pathology: the first fossil occurrence of Schmorl's nodes

Abstract

ABSTRACT A plesiosaur specimen from the Lower Lias (Lower Jurassic) of England displays lesions of the vertebral end-plate in 24 of the 27 preserved centra. A single Schmorl's node is visible towards the ventral margin of the anterior end-plate in each of eight vertebrae. The herniated intervertebral discs have penetrated the cortex of the adjacent vertebral bodies, forming the typical mushroom-shaped cavities of Schmorl's nodes. BRSUG 26539 represents the first fossil, reptile or marine organism to be diagnosed with Schmorl's nodes, a disease most commonly associated with the human spine and a bipedal stance. Compressive stresses arising from bending loads within the ‘archer's bow’ system of the plesiosaur trunk region are concentrated towards the ventral margin of the vertebral end-plate and may explain the location of Schmorl's nodes in the posteriormost cervical vertebrae. Degeneration of the vertebral column due to old age, a congenital weakness in the vertebral end-plates, or bending moments and torsional loadings induced by the weight of the head and long neck are possible explanations for the development of Schmorl's nodes in this plesiosaur. Osteoporosis is an unlikely cause of the disease in this specimen due to the pachyostotic nature of plesiosaur vertebrae.