Saturday, 15 March 2014

The power of X-rays

It is often the case that fossil specimens are preserved within a matrix of rock where some parts lay over other parts. In the case shown below, the skull of this pterosaur is laying across the wing bones. Without some form of scan, the skull would have to be removed to see the bones below.
An X-ray of the fossil matrix can, in many cases, reveal the bones that are concealed below the skull. X-rays of fossils depend upon variations in radio-density of the materials. If the fossil bones are replaced with different material than the surrounding matrix and have variations in density within the structures themselves, an X-ray can reveal quite a lot of detail.
Interpretation of X-rays is quite a skilful task. analysis of detail requires a great deal of knowledge about the nature of the materials that the X-rays are passing through. The analysis of this X-ray shows the interpreted wing bone positions marked.
It shows in this case, that the Wing Metacarpal has sustained a stress fracture, probably during launch for flight. This break does not have the radial signature of an impact fracture and it was probably caused by the bone at the point of fracture being too thin to sustain the stress of extreme latteral pressure. If this animal fell into the sea with one wing broken in this way, it would be unable to take off and would probably have starved to death or become a victim of small marine carnivores picking at its flesh.  There is no lower jaw associated with these remains, so that probably detached prior to fossilization.
The fossil X-ray will only show the preserved hard parts of an animal. The use is very limited, unlike this X-ray of one of my cats, which shows a good deal of soft tissue structure and variation in bone density where the bones are in their living orientation.