It is not likely that "Dinocephalosaurus" used its long neck for breathing by extending it vertically. If it tried to do so, the difference in pressure between the surface and its torso would be sufficiently extreme such that its lungs would not have inflated. Thus, in order to breathe, "Dinocephalosaurus" would need to approach the surface with a nearly horizontal neck. The horizontal posture of the neck would also have facilitated locomotion at the surface, due to its long profile increasing its "hull length" and reducing the effect of resistance from waves.