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What colour were fossil animals?

Dr Michael Pittman of the Vertebrate Palaeontology Laboratory, Department of Earth Sciences, The University of Hong Kong led an international study with his PhD student Mr Arindam Roy that evaluates fossil colour reconstruction methods to propose a new study framework that improves and expands current practice. The paper was recently published in the journal Biological Reviews.

What colour were fossil animals?
A pristine specimen of the feathered dinosaur Anchiornis huxleyi showing its colour patterns.
Melanin was first identified from an animal from this species [Credit: Xiaoli Wang]
"People are fascinated by the colour and pattern of dinosaurs and other extinct animals because these aspects can tell you so much about an animal. Just think of a zebra and a peacock. We evaluated everything we know about fossil and modern animal colour and used that knowledge to propose a framework to improve how we reconstruct fossil colour in the future." said Dr Pittman.

What colour were fossil animals?
A life reconstruction of the feathered dinosaur Anchiornis huxleyi based on fossil evidence
of its colour and patterning. This evidence included inferences about melanin pigments
[Credit: HKU MOOC/Julius T Csotonyi/Michael Pittma]

Colour and patterns are critical to understanding the life, ecology, physiology and behaviour of animals. These colours are produced when light interacts with pigments and the structure of animal tissue. Common naturally-occurring animal pigments include melanin, carotenoids, porphyrins pterins, flavins and psittacofulvins which produce colours ranging from black and grey to yellow, orange and green.

What colour were fossil animals?
Distribution of different colour-producing pigments among vertebrate animals. Covers fish, amphibians,
mammals, lizards, snakes, crocodilians and extinct archosaurs including non-avialan dinosaurs
 and birds. Dotted lines indicate stem groups; bold lines indicate crown groups
[Credit: HKU]
Feathered dinosaur fossils instrumental to understanding the origin of birds were the first animal fossils to yield evidence of melanin, the colour pigment we also have in our eyes and hair. In the last ten years, colour patterns have been reconstructed in over 30 fossil animals including birds, non-avialan dinosaurs and mammals, providing a unique opportunity to test ecological and behavioral hypotheses that were previously out of reach. Unfortunately, our knowledge of other pigments is scarce in the fossil record as these non-melanin pigments are more difficult to fossilise. This incomplete knowledge and the lack of a standard study approach have been prevailing challenges to the reconstruction of colour in fossil animals.

Credit: HKU                               

Co-author Dr Evan Saitta of the Field Museum of Natural History, Chicago, USA said, "We are in the golden age of multidisciplinary techniques in palaeontology. This is the first comprehensive study that not only critically evaluates the currently available methods, but also provides a reliable and repeatable framework that covers all vertebrate pigment systems not just melanin alone."

What colour were fossil animals?
(A) New framework for reconstructing fossil colour in animals. Solid lines indicate confirmed steps; dashed lines indicate
potentially useful steps that deserve further investigation. (B) Sediment-encased maturation is method of producing artificial
fossils that helps to better understand how fossils are preserved. Abbreviations: ESI-MS, electrospray ionisation mass
spectrometry; FIB-TEM, focused ion beam-transmission electron microscopy; FT-ICR-MS, Fourier-transform ion cyclotron
resonance mass spectrometry; HPLC-MS, high performance liquid chromatography; LSF, Laser-Stimulated Fluorescence;
 MLR, multinomial logistic regression; NMR, nuclear magnetic resonance; PCA, principal components analysis; PPC,
peak probability contrast; Py-GC-MS, pyrolysis-gas chromatography-mass spectroscopy; synchotron-LDPI,
laser desorption-ionisation; TDCA, thiazole-4,5-dicarboxylic acid; TOF-SIMS, time of flight
secondary-ion mass spectroscopy; UV, ultra-violet light [Credit: HKU]
The new palaeocolour reconstruction framework proposed by Dr Michael Pittman, Mr Arindam Roy and their international team comprises four main steps: (1) Map the known or suspected extent of preserved colour and patterns in the specimen; (2) Search for pigment-bearing microstructures using electron microscopy e.g. microstructure shape can be used to identify melanin-based colours like black, grey and brown); (3) If melanin-based colours are not detected, use high-end chemical analysis techniques to detect biomarkers of other pigments (4) Use reconstructed colours and patterns to test fundamental hypotheses related to animal physiology, ecology and behaviour. The new framework overcomes past challenges by incorporating the chemical signatures of different pigments, large and small-scale anatomical details visible in fossils as well as the potential for different pigments to fossilise. This framework provides background context for the evolution of colour-producing mechanisms and is expected to encourage future efforts to reconstruct colour in more fossil animals including non-dinosaur reptiles and mammals.

Mr Roy, the study's first author and a Hong Kong PhD Fellow said, "I am really excited by the course we have charted in this review study as I will be tackling many of the key issues we identified during my PhD studies at HKU."

Source: The University of Hong Kong [September 22, 2019]


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