Fossilized 99 million year old bird wings discovered in amber

The wings are the first discovered to show hair follicles and feather arrangements of the ancient birds

The findings were published today in a Nature study and help provide a full, three-dimensional picture of what these prehistoric birds looked like. The study's lead author, Ryan McKellar, explains the significance of these results and why amber is the perfect material to examine ancient fossils.

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DIP-V-15101 ("Rose"), showing overlapping flight feathers erupting from amber

ResearchGate: Can you explain the significance of your recent findings?

Ryan McKellar: The specimens in our study provide the first records of feathers in amber that have been preserved alongside skeletal material – previous work has involved isolated feathers that are difficult to tie to a particular group of birds. This form of preservation allows us to identify the source animal with confidence, and draw conclusions about the feather-bearer. The bones and body size of the specimens in our study indicated that we were dealing with juveniles belonging to a group called Enantiornithes, which are closely related to modern birds, but have teeth and a different configuration of bones.

Preservation in amber allowed us to examine the distribution of feathers on the wing surface, microscopic details of feather structure, and visible traces of pigmentation within the specimens. These observations confirm that enantiornithines hatched with adult-like plumage, unlike the downy feather coat that is present in most modern precocial birds.

RG: How did you find this specimen? How do you generally go about finding fossils in amber?

McKellar: These specimens were purchased in an amber market in Myanmar by the project leader Lida Xing, in 2015. Burmese amber is one of the few deposits from the Cretaceous that is commercially mined and exported, and it has been a very important source of insect fossils over the last twenty years. Most of my work on fossils in amber involves searching for amber in the field, predominately in sedimentary rocks across western Canada. In a general sense, we tend to search for amber in rock units produced in swampy settings, digging through coal deposits from swamps, shale from flooding events, or sandstone left behind by river channels. We find amber in many of the same places that we find plant fossils, and also alongside vertebrates in bone beds.

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Mapping flow lines within the amber using UV light in specimen DIP-V-15100 ("Angel Wing")

RG: What are the benefits of examining fossils that have been preserved in amber as opposed to other materials?

McKellar: 
Amber tends to only trap and preserve small insects and fragments of larger animals, but it preserves specimens in unmatched detail. Compression fossils (those preserved in sedimentary rocks) face limitations, because sediment size and chemistry influences the amount of 3-D detail recorded. Amber retains much of the three-dimensional arrangement of fossils, and shields them from things like chemical exchanges with the surrounding rocks and pore fluids. Ultimately, this produces fossils that accurately record details at a micrometer-scale, and include visible traces of coloration that are rarely encountered elsewhere. Amber also has the unique ability to preserve behaviors, for example struggle marks or mating in insects. It also demonstrates ecological associations in high resolutions – for example, if various organisms are trapped within the same piece of amber, they must have lived in close proximity.

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A big wing image of DIP-V-15101 ("Rose"), showing claw and pale spot in plumage.

RG: What types of specimens do you most regularly find in amber?

McKellar: The most commonly encountered arthropod specimens in Cretaceous amber tend to belong to groups such as mites, flies, wasps, and bugs. However, the most abundant groups vary as you move from one deposit to another, particularly in Cenozoic amber. Generally speaking, the most common inclusion in most of the deposits that I have seen are insect feces and plant hairs.

RG: How do specimens become fossilized in amber?

McKellar: Resin from trees engulf an inclusion, which provide an environment in which resin acids and terpenoids suppress the process of decay and rapidly dry out the specimen. As the resin forms a plastic-like substance as it hardens, the inclusion is shielded from physical damage and further chemical interactions with its surroundings. If the inclusion is sealed within the amber, it slowly matures, leaving a cavity in the surrounding amber.

Image credits Royal Saskatchewan Museum.