Patterns discovered on dinosaur eggs have revealed that the brightly coloured shells seen in birds today have an ancient origin.

Birds are the only modern animals that produce colourful eggshells covered with a huge range of markings and shades using a combination of just two pigments – red and blue.

The discovery of these pigments in the fossilised eggshells of dinosaurs similar to Velociraptor suggests they first emerged in members of this lineage before some of them evolved into birds.

Like many birds alive today, an analysis has revealed these prehistoric reptiles laid eggs speckled with colourful spots.

The discovery is the latest piece of evidence demonstrating that many of the features now associated with birds first appeared in their dinosaur forebears.

“Coloured eggs have been considered a unique bird characteristic for over a century,” said Dr Mark Norell of the American Museum of Natural History, one of the study’s coauthors.

An assortment of bird eggs alongside a fossilised shell (right) belonging to a small carnivorous dinosaur (Jasmina Wiemann/Yale University)

“Like feathers and wishbones, we now know that egg colour evolved in their dinosaur predecessors long before birds appeared.”

According to lead author Jasmina Wiemann of Yale University, bird experts have assumed for two centuries that the patterns seen in bird eggs evolved independently multiple times in their family tree.

However, their findings suggest that colour evolved just once, and the same pigments have been carried through to the present day.

The research team studied 18 fossil dinosaur eggshells held in museums around the world, using non-destructive laser imaging techniques to detect tiny traces of pigments.

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Only shells belonging to small carnivorous Eumaniraptora dinosaurs bore evidence of patterns, while larger dinosaurs like Triceratops and Diplodocus – which are not closely related to birds – laid pigment-free eggs.

This suggested that the smaller species were the originators of these colours. The scientists suggested they may have helped protect the dinosaurs’ precious clutches from attack, just as the patterns of bird eggs do.

“We infer that egg colour co-evolved with open nesting habits in dinosaurs,” explained Ms Wiemann. 

“Once dinosaurs started to build open nests, exposure of the eggs to visually hunting predators and even nesting parasites favoured the evolution of camouflaging egg colours, and individually recognisable patterns of spots and speckles.”

The research was published in the journal Nature.

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