Two different vertebral forms in the axial column ofLabidosaurus(Captorhinomorpha: Captorhinidae)

Abstract

The axial column inLabidosaurusis thoroughly described. Two different vertebral “morphs” are found to occur in this genus. One type is that which is classically illustrated forLabidosaurus, while the other shows alternation in height and construction of the neural arches and neural spines. A brief description of the modifications of muscle attachments in alternating forms is outlined. Analysis shows that such a structural modification probably allowed (more) efficient dorsiflexion and lateral flexion of the vertebral column. The occurrence of alternation of neural spine and arch structure is probably a primitive characteristic, but becomes variously modified in different forms. The variability observed in the axial column suggests thatLabidosaurusmay have been sexually dimorphic, or that the genus may consist of two different species.