Confuciusornis

Discovery and Naming

Confuciusornis is a small dinosaur that lived long ago during the Early Cretaceous Period, about 125 to 120 million years ago, in what is now China. It was about the size of a crow and had a beak without teeth. This was different from some of its relatives that still had teeth.

Confuciusornis was named after the famous Chinese philosopher Confucius. Many fossils of Confuciusornis have been found, helping scientists learn more about how birds evolved from their dinosaur ancestors.

History of discovery

In November 1993, scientists saw a fossil bird. They soon found another one. In 1995, they named these birds Confuciusornis sanctus. The name mixes the philosopher Confucius with the Greek word for bird, "ornis".

These birds lived during the Early Cretaceous Period, about 125 to 120 million years ago, in what is now China. Many fossils of Confuciusornis have been found, helping scientists learn about these old birds. At one place, many fossils were found near each other, suggesting a group of birds may have been affected by a volcanic eruption.

Description

Confuciusornis was about the size of a modern crow, with a total length of 50 centimetres (1.6 feet) and a wingspan of up to 70 cm (2.3 ft). Its body weight may have been as much as 0.5 kilograms (1.1 lb) or as little as 0.2 kg (0.44 lb).

Confuciusornis shows a mix of simpler and more advanced traits. It was more "advanced" than Archaeopteryx because it had a short tail with a pygostyle (a bone formed from a series of short, fused tail vertebrae) and a bony sternum (breastbone). However, it was more basic than modern birds. It had large claws on its forelimbs, a simpler skull with a closed eye-socket, and a relatively small breastbone.

The wing feathers of Confuciusornis were long and looked modern. The primary wing feathers of a 0.5-kilogram individual reached 20.7 centimetres in length. Many specimens have a pair of long, narrow tail feathers, which grew longer than the rest of the body.

Classification

Scientists put Confuciusornis in a group called Confuciusornithidae in 1995. They thought it was close to another group called Enantiornithes, but later found it was linked to them in a larger group called Sauriurae. Some scientists did not agree.

In 2001, scientists thought Confuciusornis might be close to a group called Ornithothoraces. By 2002, more studies agreed, placing Confuciusornis in a new group called Pygostylia, making it one of the first members. Confuciusornis had some features that show its place in bird evolution. It had a simpler skull than Archaeopteryx, but it was the first bird to lose its long tail and develop fused tail bones, called a pygostyle.

One of its close relatives, Changchengornis, lived in the same area and also had long tail feathers, like some more advanced enantiornith birds. True tail fans came later in ornithuromorph birds.

Paleobiology

The big, soft foot pads, small foot pads, and curved foot claws of Confuciusornis are traits shared with modern birds that live in trees. This suggests it may have lived a similar life.

Comparisons between the rings around the eyes of Confuciusornis and modern birds and reptiles show it may have been active during the day, like most birds today.

Flight

Confuciusornis has long been thought to be a good flier because of its very long wings with special feathers. Other features that help with flying include: a joined wrist, a short tail, a strong breastbone with a central ridge, a special bone in the wing, a large bone area in the shoulder, a strong ulna (forearm bone) and a big bone in the wing hand. However, it may have flown differently because it could not turn its arm fully behind its body, and its smaller breastbone ridge suggests it could not fly for long periods.

Some people have said Confuciusornis could not fly well. Some thought it used its big thumb claws to climb trees. Others thought climbing was unlikely.

There is also debate about the strength of its feathers. Some researchers said the main shafts of the feathers were too thin to stay strong during flying, suggesting Confuciusornis might have only glided flight. Others disagreed, saying more accurate weight guesses allowed powered flight even with thinner shafts.

In 2016, researchers used special light on two specimens and found the feather shafts were strong, and the wing shape matched birds in forests or gliding birds. The layer of tissue would have given lift and kept the feathers straight, showing Confuciusornis could fly, at least for short times.

Tail feathers

Many Confuciusornis specimens have a single pair of long, stream-like tail feathers, like some modern birds. Some specimens without these feathers have very well-preserved feathers elsewhere, showing the absence is not due to poor preservation. Long tail feathers are found in about 5 to 10% of known specimens.

There was debate about why some specimens have long tail feathers and others do not. Some researchers thought it might show differences between males and females, with the long feathers used in courtship. Others agreed this was a reasonable idea, noting that in modern birds, the length of special feathers often differs between males and females.

Other ideas for why long tail feathers are often missing include the possibility that birds without them died at a certain time. Others suggested Confuciusornis may have shed these feathers to defend itself. Researchers said even the presence of two groups, one with and one without long tail feathers, should be considered.

Reproduction

In 2007, a Confuciusornis skeleton was found with an egg near its right foot — the first possible egg linked to this genus. The egg is round and measures 17 mm across, slightly smaller than the bird's head. In modern birds, larger eggs are common in species where baby birds depend fully on their parents, while smaller eggs are found in species where baby birds are more developed and independent. Since the estimated egg of this specimen was about 30% smaller than expected for a modern bird, it is likely that Confuciusornis babies were independent when they hatched.

Growth

Growth can be studied by looking at the inside structure of bones. The first study on Confuciusornis used special scanning electron microscopy to look at a thigh bone. Because the bone had many blood vessels and showed only one line of arrested growth, researchers said growth was fast and continuous, like in modern birds.

In 2008, researchers studied many specimens to see the link between body size and long tail feathers. They found two clear size groups. They concluded that either the sexes were the same size or both had long feathers.

The idea of growth was questioned, with some saying the smaller size group was too big to be the youngest stage.

Chiappe and others defended their findings, saying the growth period was likely longer than thought. They said bone growth happened at different rates and had pauses, as shown by the lines of arrested growth. So, growth took several years, not less than 20 weeks.

Possible medullary bone

A study found medullary bone in the long bones of a short-tailed specimen, but not in three long-tailed ones. In modern birds, medullary bone only forms temporarily in females to help make eggshells. So, researchers suggested short-tailed specimens were females, and long-tailed ones were males. The female specimen had finished its fast growth phase but was still smaller than the biggest Confuciusornis specimens. At least two lines of arrested growth were seen, showing growth over several years. Long tail feathers were found in small individuals. If tail feathers show maturity, it happened before the birds reached full size, unlike in birds but similar to some dinosaurs.

Diet

In 1999, a scientist thought Confuciusornis probably ate plants, noting its beak curved upward and was not sharp for catching prey.

In 2006, researchers found a specimen with several ribs of a small fish, likely Jinanichthys. These fish bones were in a tight group about 6 mm across, near the bird's seventh and eighth cervical vertebrae. While it is unknown how often Confuciusornis ate fish, this finding did not support a plant-only diet. Since no specimens had stomach stones (swallowed by birds to help digest plants), researchers suggested it ate both plants and animals, similar to crows.

Paleoenvironment and paleoecology

Confuciusornis was found in the Yixian and Jiufotang Formations, which are part of the Jehol Biota. These rock layers contain lots of tuff from volcanic eruptions, along with shale and mudstone. Scientists can figure out the age of these formations, which is about 125 to 120 million years old, by studying the tuff.

The fossils of Confuciusornis and many other creatures were preserved because of flooding and volcanic ash. This created very flat fossils, and even some soft parts like feathers were saved. The climate back then was cool and temperate, with an average temperature around 10 °C. Many different plants and animals lived here, including many types of insects, fish, salamanders, mammals, lizards, pterosaurs, and dinosaurs. Some of these dinosaurs had feathers, showing how birds might have evolved from them. There were also many early birds in this area.