So, I am aware that it has been a long, long time since I last posted a blog. I am sorry for that. I am writing up my PhD, which takes a lot of time and effort and I am very close to submitting. The small amount of spare time I have, I have spent making the most of my personal life rather than writing blogs. Anyway, with any luck I can remember how to do this so here goes.
This blog posts deals with colour in the fossil record, and particularly with colour in ichthyosaurs. This focuses on the paper published in 2014 by Lindgren et. al. (2014).
Colour is rarely seen in the fossil record as soft parts of the body (such as skin or feathers) are not often preserved. Despite this, in a few rare cases colour can be seen. It has been reported previously, predominantly in insects (Fig. 1) but also in feathers (McNamara et. al., 2012) where exceptional preservation occurs.
So how does this relate to ichthyosaurs? Well, exceptionally preserved specimens of ichthyosaurs are known, typically from the Holzmaden area of Germany. Many of these specimens preserve a soft bodied outline which has already contributed to knowledge of ichthyosaurs (Fig. 2). Without these outlines, the dorsal fin and the semi-lunate tail shape would not have been known if only skeletal material was preserved. These outlines have generally thought to have been the result of a bacterial mat that built up during decomposition.
Lindgren et. al. (2014) analysed these soft body parts of an ichthyosaurs, carbonised scales of mosasaurs and remains of a leatherback turtle using SEM (scanning electron microscope) and ion mass spectrometry. Under SEM, the black material surrounding the skeleton is comprised of micro-meter sized spherical and rod shaped bodies (Fig. 3). These bodies strongly resemble melanosomes that are found in extant lizards and feathers. Melanosomes are an organelle that creates and stores melanin, a natural pigment that creates darker colours in organisms. In humans it is found in hair and more can be creates in sunlight, resulting in a tan. Further micro analysis shows that these features are more associated with the ‘skin’ rather than the surrounding rock.
Ion mass spectrometry produced negative-ion mass spectra from specific smaple regions of the ichthyosaur. The results closely match the spectrum obtained from natural eumelanin. Eumelanin is a type of melanin that relates to black and dark-brown colours.
These results all indicate that the body of an ichthyosaur was a dark grey/black. The areas sampled all showed a similar result which suggests that there is no counter shading with lighter underparts, but were completely dark. Many modern large open ocean organisms are this dark grey/black colour such as whales and dolphins and this result is consistent.
However, it is important to remember that, although the results are sound, the analusis has only been conducted on a single specimen from a single species of ichthyosaur so far. It will be interesting to see if any other colours or colour patterns emerge in future studies.
As always, thanks for reading. Feel free to leave any feedback.
Lindgren, J., Sjovall, P., Carney, R. M., Uvdal, P., Gren, J. A., Dyke, G., Schultz, B. P., Shawkey, M. D., Barnes, K. R. & Polcyn, M. J. 2014. Skin pigmentation provides evidence of convergent melanism in extinct marine reptiles. Nature. 0:1-4
McNamara, M. E., Briggs, D. E. G., Orr, P. J., Noh, H. & Cao, H. 2012. Original colour of fossil beetles. Proc. R. Soc. B. 279:1114-1121