The discovery of a small herbivorous dinosaur named Kulindadromeus in 2014 changed the origin of feathers as we know it. Our understanding of when feathers appeared on dinosaurs has always been rather unclear. When news broke in 1996 that a small dinosaur named Sinosauropteryx had been discovered bearing feathers, it overturned almost every previous notion about the dinosaurs. While they were previously characterized as slow, large, lumbering lizards, the new discoveries portrayed them as fast, nimble and intelligent creatures with complex social lives. Where in the past their ancestry was tied closely to that of crocodiles, the discovery of feathers on a dinosaur confirmed what had been loosely theorized in years previous: that birds are the direct descendants of the dinosaurs. In other words, modern birds ARE dinosaurs. Indeed, the discovery of Sinosauropteryx started a revolution in the field of paleontology for years to come. That was until Kulindadromeus came along and forced paleontologists to reconsider 3 major concepts.
The Origin of Feathers: Not Just Meat-Eating Dinosaurs
Kulindadromeus changed the origin of feathers as we know it. Sinosauropteryx, discovered in 1996, belonged to the theropod dinosaurs (meat-eaters), more commonly known as the group of dinosaurs that contain species such as Allosaurus and Tyrannosaurus. After the discovery of Sinosauropteryx, dozens of other feathered theropods have been discovered with traces of feathers, ranging in size from the “Dino-bat” Yi Qi to the elephant-sized Tyrannosaurid Yutyrannus. Since all of these finds were from theropods that lived between the late Jurassic to mid-Cretaceous of China (between 165 and 125 million years ago), it was widely presumed that feathers had evolved around this time and had blossomed across the theropod family tree in the millennia that followed. Given this, the paleontological community seemed shocked when it was announced in 2014 that a small ornithischian dinosaur (plant-eaters), Kulindadromeus, had been unearthed in eastern Russia with a full plumage of downy feathers. With the discovery of a small herbivore who possessed feathers, paleontologists were forced to reconsider when feathers first evolved on dinosaurs, as well as which species of dinosaurs possessed feathers entirely.
The Evolutionary Tree
To understand why Kulindadromeus is so important, we must understand where it fits on the dinosaur family tree. Within the dinosaur family tree lay 2 separate branches; The Saurischians (theropods and sauropods) and the Ornithischians. The two branches likely diverged from a single common ancestor during the Triassic period, at a time previous to 230 million years ago. Kulindadromeus belongs to the Ornithischians, which are more commonly known as the “bird hipped” dinosaurs. Within this family lie dinosaurs such as Stegosaurus and Triceratops. Despite the name, the Ornithischians weren’t closely related to birds; that honor belongs to the theropods.
As previously stated, since the feathered dinosaur remains that were found had all belonged to theropods, it was believed that feathers had evolved sometime after the split between the two branches. With the discovery of Kulindadromeus, this notion was invalidated. It was hypothesized that if an Ornithischian that lived some 70 million years after the split between the two lineages possessed feathers, then feathers must have evolved much earlier than previously thought. The possibility that the earliest Dinosaurs had some form of feathers soon became a reality. If these early dinosaurs had feathers, did they give them the upper hand in the evolutionary arms race against other Archosaurs during the Triassic? Were the Theropods more closely related to the Ornithischians than previously believed? And why did these early feathers evolve? The climate of the Triassic could hardly be described as hospitable, as long droughts and heatwaves occurred frequently. If not for insulation, then why did feathers evolve? It would seem that they may have evolved for display; both for intimidation against potential predators and more commonly as a mating device within a species. While these questions may not have clear answers yet, expanded research into the north of Russia where Kulindadromeus was discovered may yield more answers to these questions.
How widespread were feathers in plant-eating dinosaurs?
In addition to pushing back the origin of feathers, the discovery of Kulindadromeus raises another important question: just how widespread were feathers amongst the Ornithischian family tree? Did other small Ornithischians possess feathers as well? This is more than likely, especially considering that some species similar to Kulindadromeus, such as the Australian Leaellynasaura, lived in polar climates that experienced months of limited to no sunlight. Having feathers would allow these small animals to survive year-round in the desolate climates of polar Australia. How about larger Ornithischians, such as Triceratops; did they possess feathers too? While at the moment it seems unlikely that Triceratops possessed feathers, it may have possessed hair-like filaments instead, as some of its early relatives do possess filaments along their tails. Other species of Ornithischians, such as some hadrosaurids and ankylosaurids have been discovered with fossil impressions of their skin, so it seems they would be ruled out too. Nonetheless, it is pretty funny to think about a Stegosaurus possibly being covered in feathers like that of a chicken. It is because of Kulindadromeus that these questions can even be entertained, and as such is an important new species in the understanding of the evolution of the dinosaur family tree.
With the discovery of Kulindadromeus, the idea that feathers had appeared early in the reign of the dinosaurs and expanded across the entire dinosaur family tree soon became a possible scenario. While many of the questions posed in this article don’t have clear answers yet, future discoveries of early dinosaurs may provide paleontologists with a clear picture of the origins of feathers amongst the dinosaur lineage.
This post was written for Victor Stroganov.
Hone, Dr Dave. “Siberian Dinosaur Spreads Feathers around the Dinosaur Tree.” The Guardian, Guardian News and Media, 24 July 2014, http://www.theguardian.com/science/lost-worlds/2014/jul/24/kulindadromeus-feathers-dinosaur-birds-evolution-siberia-russia.
3rd image courtesy of Andrey Atuchin. http://www.sci-news.com/paleontology/science-kulindadromeus-zabaikalicus-feathered-herbivorous-dinosaur-02079.html