Duck egg blue and oviraptor green: study reconstructs colour of dinosaur eggs

A new study of oviraptor eggshell fragments shows remarkable similarities between the reproductive biology of dinosaurs and birds

Bird eggs come in a variety of colours. From the creamy and chalky whites in doves and pigeons to spotted yellow lapwing eggs and brown chicken eggs, to the blues of blackbirds and American robins. The striking colours and patterns have inspired artists, scientists and home decor makers from Aristotle to high-end jewellers. Thanks to palaeontology, we can now add oviraptor blue-green to the spectrum.

Remarkably, only two chemical compounds bring about the whole spectrum of bird egg coloration and patterning: reddish-brown protoporphyrin IX and green-blue biliverdin. Both pigments have distinctly different chemical properties, and whereas biliverdin is distributed throughout the inner core layer of the eggshell, protoporphyrin IX is limited to the outermost eggshell layer.

Egg colouration serves several purposes, including signaling and camouflage. The concentration of the protoporphyrin IX and biliverdin is related to breeding ecology (Cassey et al., 2012). Coloured and patterned eggs are present in most modern birds which nest in the open, whereas white eggs are observed in cavity nesting and cave breeding birds (Wallace, 1889). A study of egg colouration in living birds (Kilner, 2006) concluded that the ancestral egg colour must have been white, and that egg colouration evolved independently in several groups of modern birds. However, the fact that in basal birds, such as ratites, the white eggshell does contain minor amounts of pigment seems to contradict this theory.

A new study on fossil dinosaur eggshells indicates that egg colouration is much older than previously thought, and can, in fact, be traced back to non-avian dinosaurs (Wiemann et al., 2017).

Fossil dinosaur eggs and nests are rather common in certain Late Cretaceous sites in China. Although these nests are often found without the parent dinosaur, the nests sampled in this study were assigned to the oviraptor Heyuannia huangi because eggs with a similar microstructure were found inside a female oviraptorid pelvis from one of these localities. When looked at with the naked eye, these eggs have a blackish/brownish colour, but that is unlikely to have been their original colour.

To identify the eggs’ original colours, Jasmina Wiemann and colleagues took eggshell samples of three fossil dinosaur nests and analysed them using a technique called liquid chromatography-mass spectrometry. This technique separates the chemical components of a mixture and identifies them based on their molecular mass. The eggshell’s chromatogram shows two major peaks, indicating the presence of two different molecules with different mass. These peaks overlap with the peaks for protoporphyrin IX and biliverdin from commercial pigment samples as well as with emu eggshell known to contain both pigments. This indicates that both pigments are present in the fossil samples as well. To confirm that the pigments are not the result of contamination from an outside source, such as bacteria in the surrounding sediments, a sample of the surrounding fossil matrix was subjected to analyses as well. No corresponding peaks were observed in this sample, indicating that the biliverdin and protoporphyrin IX peaks in the fossil samples result from endogenous pigments.

The open arrangement of a fossil oviraptor nest (left) and a reconstructed oviraptor nest (right) with blue-green eggs. Note that the original inclination of the eggs would have been steeper due to sediment compaction.
The open arrangement of a fossil oviraptor nest (left) and a reconstructed oviraptor nest (right) with blue-green eggs. Note that the original inclination of the eggs would have been steeper due to sediment compaction. Composite: J. Wiemann et al., 2017

Based on the peaks observed on the chromatogram and known concentrations of pigments in samples of emu shell and commercially available pigments, the researchers calculated the concentration of pigments in the fossil eggshells. In all three fossil samples, the concentration of biliverdin is higher than that of protoporphyrin, suggesting that these oviraptor eggs originally were blue-green.

This is the first time that scientist have reconstructed the colour of dinosaur eggs. While this is astonishing in itself, it has important biological implications as well. Oviraptor eggs are often found in distinct arrangements: in overlapping circles, partially stuck in nesting material and with the blunt ends exposed and pointing upwards. They were likely laid this way deliberately. In modern birds, blue-green eggs are found in emus and cassowaries. These birds lay their eggs on the ground covered with leaves and vegetation; the blue-green colour of the eggs allows them to blend in with the vegetation. This may have been the case in oviraptors as well; evidence from sedimentology and palaeoclimate reconstructions from the Late Cretaceous of China suggests that a subtropical vegetation may have covered the sites where the nests were found, thus necessitating suitable camouflaged eggs for ground nesting birds.

Furthermore, in living birds, blue-green eggs are associated with paternal care (Moreno & Osorno, 2003) and communal nesting (Handford & Mares, 1985). The reasoning behind this is that biliverdin is an antioxidant, and its deposition in the eggshell may signal the health of the female. More colourful eggs would represent more healthy females, and males are expected to contribute more to raising offspring resulting from such colourful eggs. In the majority of bird species, males participate in taking care of the offspring. Paternal care in birds has been suggested to have had its origin in dinosaurs (based on the large clutch size and absence of medullary bone in brooding adult troodontid and oviraptorid dinosaurs, Varricchio et al., 2008). The presence of blue-green eggs in oviraptors would provide additional evidence for that. Emus and cassowaries lay dark blue-green eggs and practice communal nesting, in which several females build a nest, lay their eggs in it and all participate in incubation, defence and food delivery. Although communal nesting is difficult to test in fossil animals, a preliminary, unpublished study identified chemical signatures of several maternal individuals in oviraptor nests, suggesting that oviraptors may have indeed nested communally (Yang et al., 2015, unpublished data).

This new study not only pushes back the presence of coloured eggs from modern birds all the way into (non-avian, mind you) theropod dinosaurs, but it also shows that theropod dinosaurs may have had reproductive strategies remarkably similar to those of modern birds. It is no longer a topic of discussion that birds descended from dinosaurs, but as science progresses, it is remarkable to see that so much of the physiology and behaviour that we like to think of as distinctively birdlike, actually has its roots in dinosaurs. Even colour schemes.


Cassey, P., et al., 2012. Why are birds’ eggs colourful? Eggshell pigments co-vary with life-history and nesting ecology among British breeding non-passerine birds. Biological Journal of the Linnean Society 106(3): 657-672.

Handford, P. & Mares, M.A., 2008. The mating systems of ratites and tinamous: an evolutionary perspective. Biological Journal of the Linnean Society 25(1):77–104.

Kilner, R.M., 2006. The evolution of egg colour and patterning in birds. Biological Reviews 81: 383–406.

Moreno, J. & Osorno, J.L., 2003. Avian egg colour and sexual selection: does eggshell pigmentation reflect female condition and genetic quality? Ecology Letters 6:803–806.

Varricchio, D.J., et al., 2008. Avian paternal care had dinosaur origin. Science 322 (5909):1826-1828.

Wallace, A.R., 1889. Darwinism: An exposition of the theory of natural selection with some its applications.

Wiemann, J., et al., 2017. Dinosaur origin of egg color: oviraptors laid blue-green eggs. PeerJ 5:e3706


Hanneke Meijer

The GuardianTramp

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