One of the most obvious defining things about birds is that the majority of them can fly. In order to achieve this enviable feat, they need to be able to create enough power to provide uplift and leave the ground.

Bird skeletons are unique in their design, with many adaptations over the millennia to assist in their skyward endeavour. One reason why so many can get in the air is because their bones are hollow; this also means that when they die and their bodies are eventually covered by leaves, soil and other detritus that over eons of time becomes rock compacting around their bones, those light and hollow bones are inevitably crushed under the weight of so much geology.

Feathers have long since eroded to dust. Usually, only the head remains, which can only provide so much information. It’s incredibly hard to find intact old birds, which is why the science world sits up and takes notice whenever it happens. Over the years, there have been some remarkable discoveries aiding the quest for answers as to how and when birds came into being.

The transition

The most famously complete skeleton ever found was way back in 1874 by Jakob Niemeyer, the Archaeopteryx, or Ancient Wing. It had a full set of teeth, a flat breastbone as opposed to a curved keel-like structure in today’s birds, a long, bony tail, ribs, and three claws on the wing, possibly used to hold onto its food or tree branches.

Those light and hollow bones are inevitably crushed under the weight of so much geology.

Viewed as a transitional fossil between dinosaurs and modern-day birds, it was discovered by Jakob Niemeyer in 1874 in Bavaria, Germany. Also referred to as Urvogel, German for "original bird", subsequent discoveries have since knocked it from this pedestal, but it is still pretty old at around 150 million years.

The other twelve specimens of Archaeopteryx that have been found since all show that it had body and flight plumage, and well-developed "trouser" feathers on the legs. Its body plumage was fluffy, more like down, really, like fur on mammals, but scientists believe the creature must have had some aerodynamic abilities, based on its wing shape.

However, it is thought that this ability would be about the same as a pheasant, more of a frantic flapper and then a short-distance glider rather than managing any soaring or sustained flight.

Stolen youth

In 2015 one of the most well-preserved fossils ever found was unearthed in the Araripe Basin, Brazil, a site so rich with fossils of outstanding quality from the Cretaceous period – about 145 to 166 million years ago – that it has spawned a highly lucrative yet culturally and historically damaging black market.

This illegal fossil trading is decades-old and run by extremely well-funded and coordinated criminal networks, with some pieces being sold in plain sight on eBay. The usual route for reporting any fossils found there is to the National Mining Agency, but one investigation at the end of 2020 found that a professor at Rio de Janeiro’s University of Brazil was paying quarry workers there to send anything they found to him.

One such find that could well have gone to a private collector (who in all likelihood would have no idea what they possessed) was discovered by a team of scientists from Brazil University headed by a jubilant and thankfully trustworthy palaeontologist called Ismar de Souza Carvalho, who couldn’t believe his eyes at first.

The fossil, about the size of a hummingbird dating to 115 million years ago, not only had immaculately preserved feathers, but it is also one of the few bird fossils to be preserved in three dimensions.

More of a frantic flapper and then a short-distance glider.

Long feathers known as ribbon feathers, no longer existent in today’s birds but seen many times in two dimensional fossils found in China, were so well kept that it was possible for the researchers to conclude, based on their structure and location on the body that they would not have been involved in flight at all.

The feathers displayed a row of spots, leading the team to think that their purpose was likely some kind of breeding plumage or camouflage.

Waiting for star to fall

The discovery of the world’s oldest known modern-day bird was found in March 2020 in rocks on the Belgian-Dutch border, and dates to about 66.8m to 66.7m years ago. The fossil was actually unearthed twenty years prior by an amateur fossil hunter who had then donated their findings to the Maastricht Natural History Museum.

It was there that Daniel Field from the University of Cambridge, UK and his team of international scientists carried out CT scans on some items that showed interest. Seeing some bits of bone poking out from four pieces of very old rock, they digitally “removed” the layers, and were astounded to see a bird skull peering out at them. Unlike the Archaeopteryx this skull had no teeth, suggesting it was one of the oldest newest birds ever found.

This skull had no teeth, suggesting it was one of the oldest newest birds ever found.

Calculating that it was about the same size as a green-winged teal, one of the smallest ducks in the world, other features on the skull suggested it had a face like a chicken. Other fragments found in the rock pieces also suggested it had long slender legs, suggestive of a shore bird, matching the original location of discovery.

Affectionately dubbed the Wonderchicken, the bird’s official name is Asteriornis maastrichtensis; the team think it was active shortly before the asteroid strike that wiped out the dinosaurs 66m years ago, so the name references both the Greek goddess of falling stars, Asteria, and where it was found. Its discovery in Europe has also opened up debate about whether modern-day birds emerged in the southern hemisphere, a common theory – until now.

No fossil in the wrong place

There are countless pristine sites across the world that have just the right mix of sediment and rock formation to preserve the remains of long-dead birds, but the main issue is access. Who knows what lies beneath our own feet?

It stands to reason that cities like Rio de Janeiro, Berlin, San Francisco, Budapest, and so on, now far too large and permanent, are sat atop bony secrets that will never be uncovered. But if you do ever find a fossil, do remember to contact your local Finds Officer or museum who can put you in touch with the right contact.

Bird fossils are so rare that there is no price tag that could match the wealth of understanding they could hold.