Wang Min: Deciphering the code of bird origin

Source: Science and Technology Daily

Wang Min provided a picture of the interviewee in the office

The joy of research is that what we think is right today may be completely subverted tomorrow. At present, our understanding of the origin and evolution of birds is not complete, so we need to find more fossil evidence and continuously improve research methods.

Wang Min

Researcher, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences

Black square-rimmed glasses, dark blue top with jeans, sneakers, the young man in front of him, and the otaku scientist Leonard in "The Big Bang Theory" has a bit of a god. He is Wang Min, a researcher at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences, who recently won the 16th China Youth Science and Technology Award.

"In the eyes of others, I may be more boring, and I prefer to 'stay at home' to chase dramas or watch ball games on Saturdays and Sundays, rather than going out on mountain hikes and getting close to nature." Wang Min said with a smile.

Wang Min, who does not like to travel, will go to the field survey almost every year. He had no intention of landscape, but he had a fondness for stones. But what he was looking for was not ordinary stones, but bird fossils.

With the help of seemingly unremarkable stones, he and his team deciphered the code of the origin and early evolution of birds, constantly refreshing and enriching people's understanding of the origin and evolution of birds.

Rewrite the origin time of the bird type

During the college entrance examination, Wang Min's first choice was biological engineering, and as a result, he accidentally entered the paleontology and stratigraphy major.

Although both have the word biology, the two majors are very different. In the first two years, the overwhelming knowledge of geology made Wang sensitive to very boring.

A field internship changed Wang Min's view of the profession. "When what you learn in books is verified on the spot, you will really accept it and want to know more." Wang Min said.

From paleontology and stratigraphy to paleovertebrate research, to the origin and evolution of birds, Wang Min's scientific research perspective has gradually deepened, and she has gradually fallen in love with her profession from the bottom of her heart.

In Wang Min's view, his work is like a detective, facing the fossil of the creature in front of him, he needs to answer how it moved before he died, how much weight he weighed, who his siblings were, and his age at the time of death. "Although fossils can't speak, you can make bold assumptions and test them step by step." Wang Min said.

In the process of "solving the case", some surprises will appear from time to time. In 2015, Wang Min's team, in collaboration with other institutions, discovered the world's oldest fossil of the bird type to date and named it Miman Archaeopteryx. The paper was published in Nature Communications, and Wang Min was the first and corresponding author of the paper. The work was reviewed by Science at the time as "the most important discovery in the study of the early evolution of birds in the last 10 years."

Previously, the world's oldest fossil of the bird type was found in the Yixian Formation of the Rehe biota, about 125 million years ago. The new specimen we studied was found in the Huajiying Formation in the Sichakou Basin of Fengning, Hebei Province. Wang Min introduced that isotopic dating shows that the bird fossil layer of the Huajiying Formation is about 130 million years old, so the new specimen represents the oldest known fossil record of the bird type, and pushes the origin time of the bird type to the prehistory by at least 5 million years.

Mesozoic birds mainly include present-day bird-type species, anti-birds and some more basic birds. The present bird type is one of the most advanced groups in the Early Cretaceous, from which living birds evolved.

Wang Min conducted extensive analysis of the phylogeny of Mesozoic birds. The results showed that the Mimanian bird was more progressive in the system tree than other red mountain birds of later times. The more advanced systematic location and earlier appearance time of the Miman archaic bird show the inconsistencies in the relationship between stratigraphy and lineage, indicating that the origin of the present bird type is earlier than the existing understanding. At the same time, the origin and differentiation of other primitive bird branches other than Archaeopteryx were also advanced to the Late Jurassic, the Early Cretaceous.

Discover the oldest bird feeding mass

Not only focusing on the origin of birds, what and how early birds ate, is also the focus of Wang Min's attention.

Over the long evolutionary history of birds, they have lost teeth and thick upper and lower jaws in favor of lightweight beaks, while also evolving a special digestive system that allows them to swallow food in a hunch without chewing.

"For things that are difficult to digest, such as bones and hair, birds will spit it out of their mouths in the form of a dough, rather than excreting it with feces like other vertebrates." Wang Min introduced.

The stomachs of birds differentiate into a glandular stomach and a muscular stomach, which is able to secrete digestive juices to soften food, while the muscular stomach mainly mechanically grinds food. The pylorus between the musculature and small intestine of birds is narrow and the wall of the small intestine is thin, so it is difficult for indigestible things such as bones to pass through the pylorus and remain in the musculature.

With the contraction of the muscular stomach, the squashed food mass is then transported forward by the gastrointestinal tract, through the glandular stomach, the esophagus, and finally spit out of the mouth. Such a digestive process can not only enable birds to quickly swallow food into the body, reduce the chance of prey, but also quickly excrete things that are difficult to digest and lose weight.

While studying a specimen of the Jiufotang Group's anti-bird species found in the early Cretaceous of western Liaoning, Wang Min discovered a spindle-shaped agglomerate under its humerus that contained bone fragments of wolffin fish. After comparing it with the digestive system of living birds and crocodiles, Wang Min believes that the agglomerate is the bird's feeding mass.

"This specimen is about 120 million years old, the oldest fossil record of bird-eating clutters to date." Wang Min introduced.

The hypothesis of independent evolution of the coccyx and tail feathers of early birds is proposed

In the evolution of dinosaurs to birds, the coccyx changes were most significant. Unlike the long coccyx bones of dinosaurs, the coccyx of living birds is significantly shortened, especially the last few tail vertebrae heal into a tail bone.

The tail bones of living birds are plough-shaped when viewed sideways, and their surfaces are attached to muscle and fibrous fat, so that they can control the expansion and closure of the fan-shaped tail feathers, which is an important condition for realistic flight. Previously, such a plough-shaped caudal bone appeared only in the present bird type, and the fan-shaped tail feathers were mostly found in the present bird type; in contrast, in the anti-bird and other more primitive birds, the tail variety bone morphology was single and long rod-shaped, and the fan-shaped tail feathers rarely appeared in these birds.

Therefore, researchers previously generally believed that the plow-shaped caudal bone and the fan-shaped tail feathers evolved simultaneously. However, Wang Min's team's study of a fossil of a pre-Cretaceous anti-bird found 130 million years ago, the polydonal-feathered bird, challenged this view.

The researchers found that the caudal bones of the multi-toothed shin-feathered bird were significantly shortened, and the relative length was similar to that of today's bird type. More importantly, the end of the caudal plexus of the multi-toothed shin-feathered bird curves to the dorsal side, resulting in the exact same plough-shaped caudal miclon as the bird type today. However , the multi-toothed tibia do not have fan-shaped tail feathers; instead , its tail feathers are non-pinnate , suggesting that the caudal bones of the present-day bird type have evolved in parallel at least in anti-birds such as the multi-toothed tibia. This means that the hypothesis of "co-evolution of the plow-like caudal bone-fan-tail feather" needs to be reconsidered.

Combining the knowledge of developmental biology and the comprehensive use of new research methods, Wang Min's team proposed the hypothesis that the tail bones and tail feathers evolved independently in the early evolution of birds, challenging the long-dominant academic view. This achievement was rated by the Chinese Paleontological Society as one of the top ten advances in Chinese paleontology in 2017.

"The joy of research is that what we think is right today may be completely subverted tomorrow." At present, our understanding of the origin and evolution of birds is not complete, so we need to find more fossil evidence, continuously improve research methods, and listen to more opinions to make our understanding more and more perfect. Wang Min said.

On the road of exploring the origin and early evolution of birds, Wang Min will go further.