Displaying eye-catching colors or outlandish behavior to catch the attention of a mate is common in nature, from the peacock, to the hummingbird, to the impossibly white teeth of 60-something real estate mogul. Scientists are claiming to have traced this phenomenon all the way back to an ancient bird-like dinosaur, which they say used a colorful ring of neck feathers to woo potential suitors 160 million years ago.
"Iridescent coloration is well known to be linked to sexual selection and signaling, and we report its earliest evidence in dinosaurs," says Julia Clarke, a professor in the Department of Geological Sciences at the University of Texas at Austin and a co-author on the study describing the new species. "The dinosaur may have a cute nickname in English, Rainbow, but it has serious scientific implications."
The fossils of the chicken-sized dinosaur, which also goes by the name of Caihong juji (Mandarin for "rainbow with the big crest"), lived in China during the Jurassic period and was discovered as a near-complete skeleton in a slab of rock in 2014. It features a long and narrow skull similar to that of a Velociraptor, but what's particularly interesting is that it has characteristics found on dinosaurs both more modern and more ancient than itself.
On one hand, it has a bony crest that is typically found on dinosaurs from earlier eras. On the other, the rainbow-colored feathers that cover the crest and neck provide very early evidence of melanosomes, organelles in animal cells that store light-absorbing pigments.
Preserved in the slab of rock where Caihong juji was found were impressions made by its feathers, along with impressions made by the microscopic melanosomes themselves. The researchers compared these melanosome impressions to those from living birds and say that more than any other species, they resemble the melanosomes of vibrantly colored hummingbirds.
Adding to the uniqueness of Caihong juji are its asymmetrical feathers, which raises the prospect of a distinct way of flight. The researchers say it is the earliest known dinosaur to display feathers of this type and, though they are found today on the wingtips of modern birds, Caihong's asymmetrical feathers were found on its tail.
"The tail feathers are asymmetrical but wing feathers are not, a bizarre feature previously unknown among dinosaurs including birds," says co-author Xing Xu from the Chinese Academy of Sciences. "This suggests that controlling [flight] might have first evolved with tail feathers during some kind of aerial locomotion."
Furthermore, Caihong's Velociraptor-like skull and short forelimbs gave it the shape similar to modern birds and set it apart from its closest relatives, a group of bird-like dinosaurs that lived in China during the Jurassic. The researchers say the rest of the family had triangular skulls and longer forearm bones than birds today.
"This combination of traits is unusual," Clarke says. "It has a rather Velociraptor-looking low and long skull with this fully feathered, shaggy kind of plumage and a big fan tail. It is really cool … or maybe creepy looking depending on your perspective."
From here, the researchers are aiming to work out how Caihong developed such a unique look, something they describe as evidence of mosaic evolution, where distinct traits evolve independently from one another.
"This discovery gives us insight into the tempo of how fast these features were evolving," says co-author Chad Eliason.