A method for estimation of lateral and vertical mobility of platycoelous vertebrae of tetrapods

A new method for the estimation of dorsoventral and lateral mobility of platycoelous vertebrae with V-shaped (radial) articular facets on the zygapophyses is developed. This vertebral pattern is observed in dinosaurs, some other fossil reptiles, and in the cervical and lumbar regions of mammals. Based on theoretical biomechanical analysis of the intervertebral discs and articulations between zygapophyses, the estimation formulas are developed and calibrated, using precise measurements of mobility between cervical vertebrae of domestic sheep. The method is applied to the presacral vertebrae of the horned dinosaur Protoceratops andrewsi. In its cervical, lumbar, and anterior thoracic regions, the differences between the calculated amplitudes of movements and the sought true values are expected to range within +/- 5A degrees. As compared to the sheep, Protoceratops shows a greater lateral mobility in the presacral region and reduced vertical mobility in the cervical region.