Archaeopteryx fossil found with preserved soft tissue proves Darwin was right all along

Archaeopteryx is often referred to as the fossil that proved Darwin right – it links today’s birds to ancient dinosaurs. Even though the first specimen was discovered over 160 years ago, this iconic fossil continues to offer fresh insights into how birds came to fly.

One of the most revealing specimens yet, the “Chicago Archaeopteryx,” was recently studied by researchers from the Field Museum.

Their findings, published in the journal Nature, were made possible thanks to remarkable preservation and advanced technology.

The fossil was put on public display in 2024 at the Field Museum, giving both scientists and the public a close look at one of the most complete Archaeopteryx fossils found to date.

Smallest Archaeopteryx fossil ever found

The Chicago Archaeopteryx was discovered in the Solnhofen limestone of Germany, a site well known for yielding all known Archaeopteryx specimens.

This particular fossil had been in private hands since before 1990. In 2022, it arrived at the Field Museum through a collective effort from fossil enthusiasts and supporters.

“When we first got our Archaeopteryx, I was like, this is very, very, very cool, and I was beyond excited,” enthused Jingmai O’Connor, the Field Museum’s associate curator of fossil reptiles and lead author of the paper.

“But at the same time, Archaeopteryx has been known for over 160 years, so I wasn’t sure what new things we would be able to learn. Our specimen is so well-preserved and so well-prepared that we’re actually learning a ton of new information, from the tip of its snout to the tip of its tail.”

This specimen is the smallest known Archaeopteryx, being only about the size of a pigeon. Its tiny bones are embedded in extremely hard limestone, making extraction especially tricky.

Preparing the Archaeopteryx fossil

Because the bones and soft tissues are nearly the same color as the surrounding rock, even identifying where the fossil ended and stone began was a major challenge. Preparing it took over a year.

The Field Museum’s fossil prep team worked under UV light to avoid damaging delicate soft tissues and used CT scans to guide their work.

“A CT scanner is essentially a machine that takes a series of X-rays, which it uses to build a three-dimensional image, based on differences in density. It lets you see inside things,” explained O’Connor.

“CT scanning was very important for our preparation process – it let us know things like, the bone is exactly 3.2 millimeters (0.1 inches) below the surface of the rock, which let us know exactly how far we could go before we would hit the bone.”

This is the first time a complete Archaeopteryx has been CT scanned and the data made available.

The UV lighting was equally important. “Previous studies have shown that there’s something in the chemical composition of Solnhofen fossils that makes the soft tissues fluoresce, or glow under UV light,” said O’Connor.

“So, our amazing prep team utilized UV light periodically through the preparation process to make sure that they weren’t accidentally removing any soft tissues that you can’t see with the naked eye.”

Unprecedented detail in this Archaeopteryx fossil

The result is a specimen that reveals more fine detail than any previous Archaeopteryx fossil.

“We’re lucky in that this specimen happens to be extremely well-preserved, but we can also see features that probably were preserved in other specimens, but which didn’t make it through cruder preparation processes in the past,” said O’Connor.

“Having the preparation of this specimen done by scientists whose goal was to preserve as much tissue and bone as possible made a huge difference.”

Why does any of this matter?

The new fossil has helped answer questions about several parts of Archaeopteryx anatomy – its skull, hands, feet, and wings.

“The bones in the roof of the mouth help us learn about the evolution of something called cranial kinesis – a feature in modern birds that lets the beak move independently from the braincase,” explained O’Connor.

She added that, although this may not sound exciting to the average person, to those who study bird evolution it is an important thing.

It’s been hypothesized that having specialized skulls for different ecological niches might have helped birds evolve into the more than 11,000 species present today.

Preserved soft tissues in the feet and hands suggest that this animal walked on the ground and possibly even climbed trees.

How Archaeopteryx took flight

One of the most debated topics in paleontology is how flight evolved in dinosaurs.

Archaeopteryx wasn’t the first feathered dinosaur, nor the first with wing-like structures, but it may have been the earliest to truly take flight.

“We think it’s the earliest known dinosaur that was able to use its feathers to fly,” said O’Connor, who highlighted this as her favorite finding in the study.

The key to its aerial ability may lie in a set of upper arm feathers known as tertials. Archaeopteryx had an unusually long upper arm bone, which could have created a disruptive gap in the wing’s surface – problematic for flight.

“If air passes through that gap, that disrupts the lift you’re generating, and you can’t fly,” O’Connor explained.

Differences in modern birds

Modern birds evolved shorter upper arm bones and specialized tertial feathers to close this gap.

Remarkably, the Chicago specimen of Archaeopteryx shows it had long tertial feathers too – something unseen in its flightless dinosaur relatives.

“Our specimen is the first Archaeopteryx that was preserved and prepared in such a way that we can see its long tertial feathers,” she noted.

These feathers, absent in closely related non-avian dinosaurs, suggest those creatures couldn’t fly.

“That tells us… Archaeopteryx could,” O’Connor added. “This also adds to evidence that suggests dinosaurs evolved flight more than once – which I think is super exciting.”

Still more to learn, 160 years later

The Chicago Archaeopteryx has already helped scientists answer long-standing questions. But this study is only the start.

“We’re learning something exciting and new from just about every part of the body that we have preserved. And this paper is really just the tip of the iceberg,” remarked O’Connor.

After 160 years, it’s clear that Archaeopteryx still has plenty to teach us. Thanks to the care and tools used in preparing this fossil, we’re seeing it in ways that past generations of scientists could only imagine.

The full study was published in the journal Nature.

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