An article published in the journal “Nature” describes a research on dinosaur eggs’ pigmentation and their link to bird eggs. A team of researchers led by molecular paleobiologist Jasmina Wiemann of Yale University analyzed 18 fossil dinosaur eggshells to look for traces of biliverdin and protoporphyrin pigments, the ones found in bird eggshells, finding them in Eumaniraptoran eggshells, a group that includes small carnivores such as Velociraptor. The conclusion is that pigmentation has a mimetic purpose that evolved in dinosaurs that created at least partially open nests.
For a long time egg pigmentation has been considered a characteristic of birds because today they’re the only vertebrates in which it exists and not in all of them because there are species of birds that lay white eggs. Species with colored eggs use two pigments to form the various colors, which can form spots and speckles: green-blue biliverdin and red-brown protoporphyrin. The eggs color reflects the preferences in nesting environments and brooding behaviors.
Jasmina Wiemann is a molecular paleobiologist active in researches that exploit modern technologies to look for fossil biomolecules. She already led a research described in an article published in the journal “PeerJ” in August 2017 which reported the discovery of traces of biliverdin and protoporphyrin in fossil dinosaur eggshells. That research already offered a different point of view about the origin of pigmentation in eggs indicating that it was another trait that birds inherited from their dinosaur ancestors.
Jasmina Wiemann’s research didn’t stop there but she went on to try to better understand the evolution of this trait. For this reason, her team analyzed 18 fossil dinosaur eggshells belonging to very different groups that lived in different places on Earth to look for traces of pigments. A high resolution Raman microspectrography technique was used that’s non-destructive, one of the advantages of this and other new analysis technologies.
The result is that the two pigments biliverdin and protoporphyrin were found in dinosaur eggshells of Eumaniraptorans (Eumaniraptora), a group that also includes modern birds and small carnivores such as Velociraptor. The traces show spots and specks similar to those of modern bird eggs and this suggests that this trait evolved in that group of dinosaurs and was inherited by birds.
This research brings confirmations to the already existing hypotheses concerning pigmentation as a form of camouflage. In dinosaurs it appears to be present in species that, as for birds, had at least partially open nests so the ones that even today are better camouflaged are the ones that are less likely to be eaten by predators.
New fossil findings and the possibility to apply new technologies to palaeontology in recent decades allowed to discover a lot about dinosaurs reproductive behaviors. The research carried out by Jasmina Wiemann on their eggs brought further confirmation that birds are dinosaurs that changed their appearance and developed flight but retained many characteristics of their ancestors.
