Archaeologists uncover feathers that shine light on 66 million-year-old dinosaur mystery

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The specimen was retrieved from a carnivorous animal, likely either a Tyrannosaurus rex or Nanotyrannus

Scientists have uncovered exceptionally preserved bird feathers within a piece of fossilised dinosaur excrement dating back 66 million years, offering fresh insights into one of palaeontology's enduring puzzles.

The specimen was retrieved from Montana's Hell Creek Formation and originated from a substantial carnivorous dinosaur, likely either a Tyrannosaurus rex or a Nanotyrannus.

The coprolite contained remnants of a Hesperornithiform, an extinct group of diving birds that disappeared during the mass extinction at the conclusion of the Cretaceous period.

Analysis of the plumage has revealed a combination of primitive and advanced feather characteristics researchers believe could illuminate why only a single lineage of ancient birds managed to survive the catastrophic asteroid impact whilst others became extinct.

David DeMar Jr, a researcher affiliated with the University of Washington's Burke Museum, made the initial discovery in 2016 whilst gathering fish fossils from the site.

Examining a small reddish-brown rock specimen, he observed something extraordinary through his hand lens. "I picked it up and scanned its surface through my hand lens, and that's when I couldn't believe what I was seeing – a tiny fossil feather," he said.

Subsequently, DeMar collaborated with Jingmai O'Connor from the Field Museum in Chicago and other colleagues to conduct detailed examinations of the coprolite through micro-CT scanning and three-dimensional surface analysis.

Within the specimen, researchers identified two leg-bone fragments measuring 18 and 12 millimetres in length, matching characteristics of hesperornithiformes previously documented at Hell Creek.

The fossilised dropping also yielded two rigid, diamond-shaped scales from a gar fish, which researchers determined the bird had likely consumed before its own demise.

The team's analysis uncovered a primary feather spanning 9.3 centimetres that displayed structural features resembling those found in contemporary pelicans, including water-repellent properties.

This feather, along with a smaller wing feather, possessed spongy, lightweight cores encased in a harder external shell — characteristics typical of modern avian plumage that provides both rigidity and minimal weight.

These advanced wing structures contrasted sharply with two fluffy body feathers discovered in the same specimen. The body feathers exhibited loosely configured branches similar to primitive plumage documented in 100-million-year-old Myanmar amber from lineages that failed to survive the extinction.

This mixture of characteristics indicated hesperornithiformes possessed an intermediate stage between ancient and contemporary feather types.

Whilst their wing and tail feathers would have facilitated effective diving behaviour, their less sophisticated body plumage would have provided inadequate insulation.

Ms O'Connor, a curator at Chicago's Field Museum who directed the research, believes the feather characteristics offer crucial evidence for understanding selective extinction patterns.

She said: "We think the types of feathers that these birds had, and/or the way they moulted those feathers, may have been one of the underlying causes of the selectivity of the end-Cretaceous mass extinction. Essentially, why some birds died out and others survived."

The asteroid collision triggered what scientists term an "impact winter", with atmospheric dust and debris obscuring solar radiation and causing dramatic temperature decreases.

Species possessing superior feather insulation would have been better positioned to withstand the subsequent frigid conditions.

Ms O'Connor emphasised the thermal function of body plumage in an interview. "These are the feathers that are responsible for keeping the body warm, right? So maybe these primitive feathers were good enough to keep them warm during the greenhouse world of the Mesozoic, but not good enough to keep them warm during this environmental catastrophe that was triggered by this impact event."

The discovery marks a significant advancement in understanding feather evolution, pushing back evidence of modern-style plumage in non-modern bird species by a decade.

Ms O'Connor described the specimen's exceptional preservation quality. "This is the best feather we've ever seen in a Mesozoic (252 million to 66 million years ago) deposit," she said, adding it resembles "a feather you could pick up off the ground."

Frank Muzio at the University of Connecticut highlighted the remarkable scope of information contained within a single fossilised dropping.

He said: "From a single coprolite, we are learning about at least three individual species morphologically, ecologically and evolutionarily. What more can you ask for?"

The findings have been published in the journal Current Biology. Ms O'Connor noted =examining feathers within coprolites represents an entirely novel research approach that could unlock further discoveries.