Five Questions about Plesiosaurs

I presented a poster for the SVPCA in Edinburgh, 1999 in the form of five questions about the anatomy and biomechanics of plesiosaurs which were especially problematical. A version of the poster adapted for the web can be found here

Over the past couple of year a number of people have emailed possible answers to some of the questions, and this has helped to clarify my thinking to some extent.

The answers to some of the questions are interdependent, and are a consequence of their locomotion and feeding behaviour. This was explored in my presentation at the SVPCA in Portsmouth, 2000. I will be adding pages based on this talk in the near (I hope) future. Some questions are left unanswered, however.

Some suggestions:

The 'hollow' centra and nutritive foramina are perhaps part of a system to control the buoyancy of the animal. The long neck, being mainly bone and muscle will be denser than water, and denser than the main body which contains lungs, and a disgestive system generating gasses. This would tend to make the head sink, and lead to a great waste of energy in trying to keep it up. If the centra contained buoyant soft tissue it would make the neck neutrally buoyant so that the animal would float horizontally without effort. If they were fluid-filled, it could be an active system wereby oil is pumped in and out of the centra via the nutrative foramina to control buoyancy actively. For feeding on the bottom, the buoyancy could be reduced so that the head would sink. For feeding on the surface from below, the buoyancy could be increased so that the head would rise.

An animal with a long neck held out in front has to make it as rigid as possible to avoid expending a vast amount of energy in correcting its' course as the poor hydrodynamics of the neck make it veer from side to side. The reduction of the rib heads to their single-headed condition could be simply to make room for the muscle masses need to stiffen and control the movement of the neck.

The long neck as an feeding mechanism seems best adapted to a sideways strike, rotating the whole body using the large paddles so that the head at the end of the lever arm of the long neck moves at a high speed.

Any more comments? - keep on sending them in!

Richard Forrest