Study Reveals Why Birds Might Have Started Laying Colorful Eggs

Study Reveals Why Birds Might Have Started Laying Colorful Eggs
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New research suggests that birds gained the ability to lay colorful eggs from some of their dinosaur ancestors, which laid eggs with similarly bright pigmentation.

As documented in a study published Wednesday in the journal Nature, a team of researchers analyzed the fossils of dinosaur eggs and found that the shells had two types of pigmentation that can be found in today’s bird eggs. According to NPR, these pigments can be combined in modern times in such a way that birds lay different colors of eggs.

A separate report from Gizmodo explained that Yale University paleontologist Jasmina Wiemann, who led the new study, first discovered last year that oviraptors laid blue-green eggs, thus bringing up the question of whether birds began laying colored eggs independently, or whether they inherited the trait from an ancestor. With that question in mind, Wiemann and her colleagues analyzed several samples from different dinosaur groups and used a laser-based technique called Raman spectroscopy to determine the types of molecules in the eggs without putting the fossils at risk.

Based on the new findings, the researchers found that theropod eggs had traces of red-brown protoporphyrin IX and blue-green biliverdin, which are the same pigments found in today’s colorful bird eggs. As there was no pigment found in the crocodilian, sauropod, and ornithischian eggs, the findings backed up the earlier theory that egg color evolved only one time as certain dinosaurs evolved into birds.

As further revealed in the study, the researchers also discovered that dinosaur eggs had spots and speckles, much like modern-day bird eggs do. This came as a surprise to ornithologist Mark Hauber of the University of Illinois, who was not involved in the study.

“We not only know now that dinosaur eggs were colorful, but they were speckled, which is a whole other aspect of diversity,” Hauber told NPR.

Hauber also theorized that dinosaurs might have laid colorful, speckled, and/or spotted eggs for the same complex reasons as today’s birds do, such as the use of “distinctive” colors and markings to ward off potential predators.

“Dinosaur eggs could have been camouflaged, they could have been individually recognized, they could have been mimetic. So there are all the functions that are associated with spotting patterns on eggs that we did not even consider for dinosaur eggs,” Hauber added.

Similarly, Wiemann and study co-author Mark Norell suggested that dinosaur eggs developed color because theropods began to lay eggs out in the open, instead of in underground or covered areas. According to Gizmodo, the researchers believe that colored eggs that blended in with the environment had a greater chance of surviving or allowed theropods to better recognize their own eggs in the event another creature would lay an egg in the same nest.

Given this unanswered question, Wiemann and her team are hoping to analyze even more fossilized eggshells to determine the exact reason why some theropods laid colored eggs and others didn’t, and if there is any relation between nest type and egg color for modern birds.