"There are no struggle marks in the amber, so we cannot know for certain," McKellar told Seeker. "That said, there is milky amber around the tail that suggests at least a little bit of moisture remained in the tail when it was encapsulated. Some of the insects trapped alongside the tail also belong to groups that scavenge."
Persons added, "The little bit of tail comes from a dinosaur probably about the size of a robin. The shape of the tail vertebrae, which we can only see in X-ray images, indicates that the dinosaur was a two-legged carnivore. It may be a hatchling or possibly an extremely small species that's new to science. So little of the skeleton is preserved that we cannot tell."
The researchers could confirm that the tail comes from a dinosaur, and not a prehistoric bird, because of its structure. They explained that the tail is long and flexible, lacking a well-developed central shaft, known as a rachis. Keels of feathers run down each side. The structure of these feathers suggests that the two finest tiers of branching seen in modern feathers, called barbs and barbules, arose before a rachis formed.
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"The development of the rachis allows feathers to form long, vaned shapes that are useful for more than just temperature, regulation, or visual signaling," McKellar said. "It provides feathers that are more useful in controlled flight."
Visible traces of pigmentation in the tail's plumage reveal that its upper surface was chestnut brown in color, while its underside was pale or white during the dinosaur's lifetime. The contrast must have been quite striking as the animal moved about.