Lungs preserved with refinement 120 million years ago, stunned scientists were studying early birds

ALBUQUERQUE, N. M. – The ancient organs seldom fossilize. Paleontologists were therefore stunned to find the incredibly well preserved remains of a lung belonging to a bird of the dinosaur era.

Initially, scientists were excited to describe the specimen of Archaeorhynchus spathula, a bird that lived about 120 million years ago, because its fossil had extraordinarily preserved feathers, including a unique pintail that is not seen in any other Cretaceous bird, but is common in birds nowadays.

Closer inspection, however, revealed that the lungs of the bird were also fossilized, which means that paleontologists had discovered the oldest "informative" fossil lung ever recorded (the oldest subject ) and the oldest fossilized lung ever seen in a fossil bird. Jingmai O 'Connor, principal investigator, professor at the Institute of Paleontology and Paleoanthropology of Vertebrates of the Chinese Academy of Sciences. [Tiny Dino: Reconstructing Microraptor’s Black Feathers]

The fossil itself comes from the formation of Jehol Lagerstätte in the early Cretaceous, in northeastern China, but O & # 39; Connor and his colleagues found it at Shandong Tianyu Nature Museum, Pingyi, where a passionate fossil collector houses the thousands of bird fossils that he has purchased decades ago.

This is the fifth described A. spathula specimen – a bird without teeth, the size of a pigeon – but by far the best preserved, said O'Connor. This is due in particular to the speckled white material in the thoracic cavity that appears to be a fossilized lung.

The discovery reveals that lung structures in early birds are similar to the lungs of modern birds, the researchers said. It means that A. spathula probably a unidirectional airflow in his lungs – the air that was introduced was largely fresh and full of oxygen, unlike that of the mammalian lungs, which is mixed with both the new air and with previously breathed air, which means it contains less oxygen.

"The lungs of birds are very different from our lungs and [had] Much more complex structures, "said Live Science in an email to P. Martin Sander, paleontologist at the University of Bonn in Germany, who did not participate in the research.They look like a pipe to bag, with air management system (the airbags) separated from the gas exchanger (the actual lung) that is preserved here. "

Live crocodilians also have lungs with a unidirectional airflow, and paleontologists have considered it ancestral in early feathered dinosaurs. But evidence of such a pulmonary structure in an early bird has been elusive until now.

Deep dive

To better see the supposed lung remains, "we went to extract samples, put them in the SEM [scanning electron microscope] and – boom – lung tissue, "said O. Connor at Live Science, as she specializes in expert skeletal anatomy on the lungs of live birds.

"I was saying," Do you think it's a lung tissue? " If you think so, none of us, digging into the earth, can argue with you, "said O. Connor .March's contribution was so critical that it became a co-researcher of the study.

An analysis of the tissue showed that it contained structures resembling blood capillaries, which absorb oxygen to help fuel the highly energetic flight of birds. "Avian flying is the most physically demanding form of locomotion, so you need a lot of oxygen," said O & # 39; Connor. [Photos: Dinosaur-Era Bird Sported Ribbon-Like Feathers]

It is possible that this unique structure was unique to Ornithuromorpha, a group of ancient birds that survived mass extinction about 66 million years ago and includes live birds. "Maybe this specialization was only in this clade and was one of the many factors that allowed [their] survival, "said O & # 39; Connor.

In addition, it seems that the fossilized lung was embedded in the ribs of the bird, just as are the lungs of the bird today. Unlike human lungs, which dilate with each breath, the lungs of birds are rigid; so they can easily inhale and exhale at the same time, said O & # 39; Connor.

The tissues do not appear to be leftovers of stomach contents, like those usually preserved as black and charred organic matter, she noted. In addition, the preserved tissue is paired, like a modern lung. There is no other organ pair whatsoever, and it is probably not the liver (which is lobed) because this organ has a high iron content and is usually kept in red, said O & # 39; Connor.

However, this specimen is not the oldest lung ever recorded. This honor goes to Spinolestes, an early Cretaceous mammal that has fossilized lungs about 5 million years older than the recently analyzed bird. But these lung fossils retain no microstructure and do not provide much information about Spinolestesbesides that, he probably had a muscular diaphragm. So, O Connor calls the A. spathula fossil "the first informative lung remains" because they have illuminated the evolution of birds.

The discoveries on the lungs are "interesting things" because they show "what was the lung of an early bird," Sander said. However, as it is very rare to see a fossilized organ, extra efforts are needed to verify that it's about a lung, he said.

"We should apply various other analytical techniques to confirm that the fossil region is really a lung," he said. "But I would not be surprised if the lung can become fossilized because of its high iron content because it is rich in blood."

The research was presented here at the 78th Annual Meeting of the Society of Vertebrate Paleontology yesterday (October 18th). It will be published in the journal Proceedings of the National Academy of Sciences on Monday, October 22.

Originally published on Science live.