No teeth, bald buttocks, big pectoral muscles, why modern birds look so weird

Confucius would never have imagined that his name would be associated with a type of Mesozoic bird discovered in later generations. These magical species are indeed like sages crossing the night sky, illuminating the glorious evolutionary path of the entire bird species. They are Confuciusornis.

Unlike those ancient creatures with difficult and obscure names, the name of Confuciusbird is very familiar to Chinese people. Confucius literally means "Master Kong", so it can also be called "Confuciusbird". It lived in the Early Cretaceous period 125 to 120 million years ago, and its model species was discovered in the Jehol Formation, which is famous in the paleontological community.

Confuciusornis fossil, housed in the Chinese Paleozoological Museum | Captmondo / Wikimedia Commons

As a representative species of the Jehol Biota, Confuciusornis is comparable to Archaeopteryx in terms of scientific research value, discussion and public awareness, and can be said to be one of the most famous Mesozoic birds. However, the discovery of such a legendary species was just an accident.

Birds from Liaoxi

The time goes back to 1993 in Liaoning, China.

A local villager named Yang Yushan accidentally discovered some fragmentary animal bone fossils (later identified as mainly skulls and forelimbs) while working in Sihetun, a suburb of Beipiao City. These specimens were then sent to the museum for preservation. Then in 1995, a team led by the famous Chinese paleontologist Hou Lianhai conducted a systematic study and finally confirmed that these remains belonged to a primitive bird, and officially named its type species "Confucius bird (C.sanctus)".

Reconstruction of the Confuciusbird | Velizar Simeonovski / Wikimedia Commons

It belongs to the genus Confuciusornithidae, an early bird at the basal stage of evolution. However, Confuciusornith is not the only valid species in this genus. The Confuciusornith dui, discovered in 1999, is the second member of this family.

Since the first Confuciusornis fossils were found in a lake sedimentary stratum, paleontologists infer that they may have lived in freshwater lakeshore wetlands with abundant food and water, just like some modern wading birds. However, crises always lurk beneath beautiful appearances. A sudden volcanic eruption killed them instantly, and rain washed the bodies of these birds to the lakebed, where they were quickly buried by silt. After billions of years, these remains of Confuciusornis, frozen in time, finally saw the light of day again.

Confuciusornis fossil, housed in the Beijing Museum of Natural History | BleachedRice / Wikimedia Commons

In order to uncover the mysteries of bird evolution, a larger-scale excavation was launched, and the world finally saw the great charm of this fossil treasure house in western Liaoning. By 2000, the number of Confuciusornis fossils found here exceeded 1,000! And most of the specimens are well preserved, even retaining clear feather marks. The large number and high degree of preservation are rare even in the world. As the reputation of Confuciusornis became popular, the Jehol Formation in Liaoning, China, has also become a new hot spot in the field of ancient bird research.

Sky Pioneer

What magic does this little bird, which is only the size of a pigeon, has a wingspan of only 0.7 meters and weighs no more than 1.5 kilograms, have that has attracted so much attention from the world?

First, compared to more primitive bird-winged creatures such as Archaeopteryx, Confuciusornis, as a transitional species, possesses more advanced apomorphic features (closer to the evolutionary features of modern birds rather than theropod dinosaurs). The appearance of Confuciusornis is like a lost fragment, filling in the missing pieces of the puzzle of non-avian dinosaur and bird evolution. Secondly, compared with other primitive birds of the same period, Confuciusornis possesses many developmental features of both modern and primitive birds, which provides us with a rare reference object for a deeper understanding of the origin and evolution of birds.

Archaeopteryx specimen HMN 1880, with a long tail made of caudal vertebrae and teeth in its mouth | H. Raab / Wikimedia Commons

For example, Confuciusornis has the following noteworthy features:

Unlike Archaeopteryx, which had a mouth full of sharp teeth, Confuciusornis is the earliest known bird with a toothless keratinous beak. Basal birds such as Liaoningornis and Yanornis, which lived in the same region and period, had teeth in their mouths, just like most theropod dinosaurs. However, Confuciusornis, which was in the early stages of its evolution, already had a beak structure that was no different from that of modern birds, which also traces the history of the disappearance of bird teeth and the appearance of keratinous beaks back to the early Cretaceous period.

The tail vertebrae of Confuciusornis, like those of modern birds, have been greatly reduced and gradually fused into a complete pygostyle. The appearance of the pygostyle not only makes it easier for birds to attach their tail feathers, but also effectively reduces their weight, paving the way for improved flight capabilities.

Skeleton of a modern bird, with the pygostyle circled in red | Squelette_oiseau / Wikimedia Commons

In order to soar better in the sky, the sternum of Confuciusornis became more prominent and specialized into a primitive keel. This groundbreaking "improvement" gave Confuciusornis more developed pectoral muscles, enabling it to fly more efficiently when flapping its wings.

The skull structure of Confuciusornis is also closer to that of modern birds. The temporal fenestra behind their eye sockets have been fused and evolved into two upper and lower fenestra, a feature never found in theropod dinosaurs, including Archaeopteryx.

The tail feathers of male Confuciusornis are longer than those of females. Scientists speculate that longer tail feathers give males an advantage in courtship. This shows that Confuciusornis, like many modern birds, has significant sexual differentiation in appearance, and Confuciusornis has become the earliest known bird with "sexual dimorphism" developmental characteristics.

A reconstruction of Confuciusornis, which also had bright colors like modern birds. | PaleoEquii / Wikimedia Commons

By studying the many unusual features of Confuciusornis, we can infer that many of the complex social behaviors of modern birds were already evident in the early Cretaceous primitive birds, which shows that the evolutionary origin of birds is much earlier than we previously thought.

Perhaps it is precisely because of the great scientific research value of Confuciusornis that a series of illegal mining activities targeting Confuciusornis fossils began in the late 1990s. The specimens of Confuciusornis became the most sought-after and most expensive "star fossils" on the black market, and thousands of precious specimens were lost overseas. According to statistics from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences, more than 80% of the Confuciusornis fossils were bought by private collectors in the United States, Germany and Japan after being smuggled out of the country, mainly because these countries have no relevant laws that explicitly prohibit the import of such fossils.

Conclusion

The process of birds conquering the blue sky can be regarded as the most magnificent page in the history of vertebrate evolution. Although the body of Confuciusornis has long turned into stone, when you look up at the sky, you can still feel the pulse of life that has continued for billions of years from the melodious bird songs.