Sunday, 12 January 2014

The Colour Of Marine Reptiles

The 160 million year old Anchiornis huxleyi with its original colouration.
In 2008 a graduate student by the name of Jakob Vinther did something remarkable. He accurately reconstructed the colouration of a dinosaur. The 160 million year old fossil was of Anchiornis, a close relative of the first birds. Its great age made it seem impossible that any trace of its colouration could still remain as fragile organic molecules are responsible for the array of hues seen in the living world and such molecules would long since have decayed during the preservation process. Yet, against all the odds, molecules of the pigment melanin were found within the remains of the feathers.

Detailed analysis of these allowed Vinther to recreate Anchiornis's colouration, with a dark grey body, white patches on the wings and a dusky red crest on its head. Since then, several other creatures have been given their original tones, particularly insects such as beetles. Now, marine reptiles have joined this small but growing list. Using the same techniques as Vinther, a team of scientists led by John Lingren from Lund University in Sweden have reconstructed the living state of a 55 million-year-old leatherback turtle, an 85 million-year-old mosasaur and a 196-190 million-year-old ichthyosaur.

Melanosomes within a cell known as a melanocyte
'This is fantastic! When I started studying at Lund University in 1993, the film Jurassic Park had just been released, and that was one of the main reasons why I got interested in biology and palaeontology. Then, 20 years ago, it was unthinkable that we would ever find biological remains from animals that have been extinct for many millions of years, but now we are there and I am proud to be a part of it,' said Lindgren about the discovery of the ancient pigment molecules.

The studies were based around patches of preserved skin from the three creatures, which contained the preserved remains of melanin-containing organelles known as melanosomes, and examining the way light would have interacted with the melanin pigments. 'Our discovery enables us to make a journey through time and to revisit these ancient reptiles using their own biomolecules,' said Per Uvdal from the MAX IV Laboratory and a part of Lingren's team.

The colouration of the marine reptiles.
All three studies yielded similar and intriguing results; namely a colour scheme known as counter-shading which is seen in marine organisms, in predator and prey alike. Animals with counter-shading have a dark back and a light underbelly. This gives them a degree of camouflage as the dark back will blend in with deeper waters when viewed from above and the light underbelly will blend with the surface when viewed from below. As the creatures in question were all reptiles, the dark back may have had a dual role. Dark colours absorb solar radiation and this may have helped the creatures capture UV light and infra-red rays from the sun, reptiles' primary source of heat.

'The fossil leatherback turtle probably had a similar colour scheme and lifestyle as does Dermochelys. Similarly, mosasaurs and ichthyosaurs, which also had worldwide distributions, may have used their darkly coloured skin to heat up quickly between dives,' continued Lindgren. From this, it is likely that these creatures lived lifestyles similar to whales, diving to depths to feed and making a brief return to the surface to warm up. It also shows how marine predators have adapted to be stealthy hunters and pass undetected by their prey.

Colour is incredibly important in the natural world. Plants use green chlorophyll to capture light from the sun and reds, blues pinks and yellows to attract mammals and insects to their flowers and fruits. Frogs and amphibians use bright tones to flaunt toxic skins to their predators. Conversely cuttlefish use camouflage to blend in perfectly with their environment. Colour dictates the lives and behaviours of millions of species. Its presence in the fossil record, and effect on the prehistoric Earth, was until recently, completely unknown.