Ornamental Tail Feathers in a Cretaceous Fossil Bird
Updated: Sep 27, 2018
J.K. O'Connor, D. Li, M.C. Lamanna, M. Wang, J.D. Harris, J. Atterholt, H. You. 2016. A new Early Cretaceous enantiornithine (Aves, Ornithothoraces) from northwestern China with elaborate tail ornamentation. Journal of Vertebrate Paleontology 36(1), e1054035.
What Is It?
My colleagues and I studied and described the anatomy of a fossil bird from Lower Cretaceous rocks in China. This fossil comes from the Xiagou Formation, which is 124-120 million years old. The site where it was found is just outside a small village in Gansu Province called Changma. This area has gained increasing renown in the past decade or so for yielding numerous beautiful bird fossils with three-dimensional preservation of bone, often with feathers also preserved. I have been fortunate enough to collaborate on study of several of these fossils, including the one I'm sharing today.
This fossil is of a small bird about the size of a scrub jay. It belongs to a group of exclusively-Cretaceous birds called Enantiornithes. The name means "opposite bird," and is a reference to several aspects of skeletal anatomy that are "opposite" what we see in modern birds. Enantiornithines superficially would have looked quite similar to birds we are familiar with today, and they do have many features in common: feathers, wings, the ability to fly, scaly feet with recurved claws. But in other ways they are quite different. Many still had teeth in their mouths, the keel on the sternum--or breastbone-- was relatively small (meaning smaller, less powerful flight muscles), and they still had claws on their remaining fingers, often quite robust (a few modern birds actually have tiny claws on their fingers, but that's a story for another day). When we study the relationship of enantiornithines to modern birds, we find these two groups are related like sisters.
Meet Feitianius paradisi, a small fossil bird with incredible tail feathers
One of the coolest things paleontologists get to do is name new taxa (that is, groups of organisms). It's especially fun to get creative with naming. We dubbed this fossil bird Feitianius paradisi. "Feitianius" is derived from "feitian," flying spirits depicted in the beautiful murals of the Mogao Grottos that are near the locality (see above picture; photo credit: https://www.buddhistdoor.net). The species name "paradisi" is a reference to our interpreted function of the elaborate tail feathers. We found evidence that these feathers were likely used in sexual display to attract mates, similar to modern birds of paradise.
So what exactly is so special about these feathers? This is the very first enantiornithine bird with three different types, or morphologies, of tail feather preserved. And furthermore (this is the really exciting part) they don't seem to be shaped to have an aerodynamic function. That means their purpose was for display, and such a large, complex display was almost certainly evolved for the purpose of attracting mates. Display feathers have been documented in other opposite birds, but never this elaborate. The complex structure seen in Feitianius suggests this was likely a male bird (in modern birds that demonstrate sexual dimorphism, only males are known to grow such large and elaborate structures). The tail of Feitianius bears a resemblance to some of nature's most famous examples of sexual dimorphism in living birds, including the greater bird-of-paradise (check out photos below for a comparison)..
Click the link at the top of the page to download the paper if you want to read more! :)