In recent decades, it’s become increasingly clear that modern-day birds are related to dinosaurs. And, while specimens of amber containing the remnants of feathered dinosaurs have been found before, an amber specimen described on December 8, 2016 in the peer-reviewed journal Current Biology is said to be the most useful yet.
Researchers at the Royal Saskatchewan Museum (RSM) in Canada, who studied the amber specimen, said that while the feathers aren’t the first to be found in amber, earlier specimens have been difficult to definitively link to their source animal. They said the feathers definitely are those of a dinosaur, not a prehistoric bird.
The new material preserves a tail consisting of eight vertebrae from a juvenile; these are surrounded by feathers that are preserved in 3D and with microscopic detail. We can be sure of the source because the vertebrae are not fused into a rod or pygostyle as in modern birds and their closest relatives. Instead, the tail is long and flexible, with keels of feathers running down each side.
The amber specimen did not come from Canada, but instead was discovered in an amber market Myitkyina, Myanmar in 2015. The first author on the study – Lida Xing from the China University of Geosciences (Beijing) – noticed the specimen at the market. Those who found it originally might have imagined the inclusion was some kind of plant. The amber was destined to become a curiosity or piece of jewelry, if Xing had not recognized its scientific potential.
The specimen represents the feathered tail of a non-avialan theropod preserved in mid-Cretaceous amber about 99 million years ago. While it was initially difficult to make out the details of the amber inclusion, Xing and his colleagues relied on CT scanning and microscopic observations to get a closer look.
•The first non-avialan theropod fragments preserved in amber are described
•Vertebral outlines, curvature, and plumage suggest a source within Coelurosauria
•Branching structure in the feathers supports a barbule-first evolutionary pattern
•Iron within carbonized soft tissue suggests traces of original material are present
In the two decades since the discovery of feathered dinosaurs, the range of plumage known from non-avialan theropods has expanded significantly, confirming several features predicted by developmentally informed models of feather evolution. However, three-dimensional feather morphology and evolutionary patterns remain difficult to interpret, due to compression in sedimentary rocks. Recent discoveries in Cretaceous amber from Canada, France, Japan, Lebanon, Myanmar, and the United States reveal much finer levels of structural detail, but taxonomic placement is uncertain because plumage is rarely associated with identifiable skeletal material. Here we describe the feathered tail of a non-avialan theropod preserved in mid-Cretaceous (∼99 Ma) amber from Kachin State, Myanmar, with plumage structure that directly informs the evolutionary developmental pathway of feathers. This specimen provides an opportunity to document pristine feathers in direct association with a putative juvenile coelurosaur, preserving fine morphological details, including the spatial arrangement of follicles and feathers on the body, and micrometer-scale features of the plumage. Many feathers exhibit a short, slender rachis with alternating barbs and a uniform series of contiguous barbules, supporting the developmental hypothesis that barbs already possessed barbules when they fused to form the rachis. Beneath the feathers, carbonized soft tissues offer a glimpse of preservational potential and history for the inclusion; abundant Fe2+ suggests that vestiges of primary hemoglobin and ferritin remain trapped within the tail. The new finding highlights the unique preservation potential of amber for understanding the morphology and evolution of coelurosaurian integumentary structures.