Saturday, 5 September 2015

Confirming The Colours Of Anchiornis

The reconstructed colour scheme of Anchiornis huxleyi
In 2010 a remarkable study was published which contained the first reconstruction of the colour scheme of a dinosaur. Pigments do occur in the fossil record, but only in exceptional circumstances and dinosaur remains are rarely preserved to a high enough level of fidelity to even think about accurate morphological reconstructions.

The paper focused on Anchiornis huxleyi, a feathered theropod and close relative of the first birds. The fossil, which came from the famous fossil beds in Liaoning, China, preserved sub-cellular structures which the researchers interpreted as melanosomes - the organelles responsible for pigmentation.

By using electron microscopy to analyse the density and shape of the structures in different parts of the body, the researchers were able to determine whether the feathers were light or dark. Critics, however, argued that the structures could have been bacterial cells on account of their similar shape and size. Recently this debate has been resolved by a study conducted by an international team of researchers led by Johan Lindgren from Lund University in Sweden. Their work focused not on the shape and density of the structures, but on their chemical composition.

Electron microscope images of structures interpreted as
melanosomes. Critiques claim that they could be bacterial cells
The team performed two different kinds of chemical analyses to see if they could detect eumelanin, the pigment responsible for pigmentations. They used both time-of-flight secondary ion mass spectrometry and infrared reflectance spectroscopy to discern the molecular signature of melanin in the samples.

Different forms of eumelanin exist, however, and so further analysis was needed to demonstrate that it was animal eumelanin. They compared the chemical signatures with the signatures of modern-day animal eumelanin. The signatures were virtually identical, except for minor contributions from sulphur in the fossil, demonstrating that the eumelanin was animal derived.

As further evidence, the signatures were compared to those from bacterial eumelanin. No match was observed, demonstrating that the structures in the fossil were not bacterial. 'We have integrated structural and molecular evidence that demonstrates that melanosomes do persist in the fossil record,' said Ryan Carney from Brown University. 'This evidence of animal-specific melanin in fossil feathers is the final nail in the coffin that shows that these microbodies are indeed melanosomes and not microbes.'