Discovered in the 19th century, scientists once believed that the first-ever dinosaur feather used to belong to the Archaeopteryx, a transitional dinosaur that lived 125 million years ago and bridged the gap between non-avian feathered dinosaurs and modern-day birds. Now, a new study has revealed that it doesn't belong to the winged dino after all – and its owner is still a mystery.

Utilizing modern-day imaging technology known as laser-stimulated fluorescence (LSF), researchers looked at the feather, which was discovered in 1861 in the southern part of Germany and have determined the iconic fossil contained the missing quill that was so hotly debated for so many years.

"It is amazing that this new technique allows us to resolve the 150-year-old mystery of the missing quill," said Daniela Schwarz, co-author in the study and curator for the fossil reptiles and bird collection of the Museum für Naturkunde, Berlin, in a statement.

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"The morphology of the complete feather excludes it as a primary, secondary or tail feather of Archaeopteryx," the study's abstract reads. "However, it could be a covert or a contour feather, especially since the latter are not well known in Archaeopteryx." Primary feathers are used for flight, while secondary feathers are used for lift and primary covert feathers are tail feathers.

Due to the missing quill, researchers had no way of knowing what part of a body it belonged to. It has been previously assumed that the feather was a primary covert feather, but the LSF technology shows it does not have the s-shaped centerline needed to be a tail feather. And given that an Archaeopteryx fossil was found shortly thereafter, researchers connected the two, despite several key missing pieces.

“LSF detected the missing quill of the isolated feather when x-ray fluorescence and UV techniques did not,” study co-author Michael Pittman told Gizmodo. “The quill only remains as a geochemical ‘ghost’ (or halo) because the original fossil material is no longer preserved. LSF demonstrated great sensitivity to this halo, recognizing previously unappreciated detection limitations in other applied techniques.’’

The research, published in Scientific Reports, shows that even fossils that are well-studied can still provide new insights.

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So if the feather does not belong to an Archaeopteryx, what creature does it belong to? It's still a mystery, but the researchers have one potential solution.

"The possibility remains that it stems from a different feathered dinosaur that lived in the Solnhofen Archipelago," the study's abstract adds.

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