Confuciusornithidae

Confuciusornithids Temporal range: Early Cretaceous, 131–120  Ma PreꞒ Ꞓ O S D C P T J K Pg N
Fossil specimen of Confuciusornis sanctus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Dinosauria
Clade:	Saurischia
Clade:	Theropoda
Clade:	Avialae
Clade:	Pygostylia
Clade:	† Confuciusornithiformes Hou et al., 1995
Family:	† Confuciusornithidae Hou et al., 1995
Type species
† Confuciusornis sanctus Hou et al., 1995
Genera
† Changchengornis † Confuciusornis † Eoconfuciusornis † Evgenavis ? † Yangavis † "Proornis" ? † Zhongornis ?

Confuciusornithidae is an extinct family of pygostylian avialans known from the Early Cretaceous, found in northern China. They are commonly placed as a sister group to Ornithothoraces, a group that contains all extant birds along with their closest extinct relatives. Confuciusornithidae contains four genera, possessing both shafted and non-shafted (downy) feathers. Some specimens probably referable to this clade represents one of the earliest known fossil evidence of primary feather moulting. ^[1] They are also noted for their distinctive pair of ribbon-like tail feathers of disputed function.

Contents

• Classification
• Biogeography
• Anatomy
• Paleoecology
• Reproduction
• References

The wing anatomy of confuciusornithids suggests an unusual flight behavior, due to anatomy that implies conflicting abilities. They possessed feathers similar to those of fast-flapping birds, which rely on quick flapping of their wings to stay aloft. At the same time, their wing anatomy also suggests a lack of flapping ability. Confuciusornithids are also noted for their beak and lack of teeth, similar to modern birds. Both predators and prey, confuciusornithid fossils have been observed with fish remains in their digestive systems and have themselves been found in the abdominal cavities of Sinocalliopteryx , a compsognathid predator.

Classification

Confuciusornithidae was first named by Hou et al. in 1995 to contain the type genus, Confuciusornis, and assigned to the monotypic clade Confuciusornithiformes within the class Aves. ^[2] The group was given a phylogenetic definition by Chiappe, in 1999, who defined a node-based clade Confuciusornithidae to include only Changchengornis and Confuciusornis. ^[3]

There are a number of features that define the clade. The most significant is the presence of a toothless jaw, which shows a more birdlike adaptation compared to Archaeopteryx. The other defining features are as follows, according to Chiappe et al. (1999): ^[3]

• There is a fork in the rostral (front) part of the mandibular symphysis, the area where the mandibles fuse together.
• The presence of a distinct maxillary fenestra (breathing hole) in the maxilla's ascending ramus.
• The deltopectoral crest of the humerus is prominent, which allows for increased muscle attachment for adductor muscles.
• The first metacarpal is not attached by bone to the other co-ossified metacarpals.
• The claw of the second manual digit is much smaller than the other claws.
• A V-shape in the sternum in the caudal end.
• The proximal phalanx of the third digit is much smaller than the other phalanges.

Confuciusornithidae is the most basal group of the clade Pygostylia, whose members possess a pygostyle, a fused set of caudal vertebrae at the end of the tail. The pygostyle replaced the longer, unfused tail found in more primitive avialans such as Archaeopteryx, ^[3] and may have served to improve flight. Pygostylia includes all modern birds, the only living members of the clade.

Additional members have been added to Confuciusornitidae since 1999. Jinzhouornis was added by Hou, Zhou, and Zhang in 2002, ^[4] and in 2008, Zhang, Zhou and Benton assigned the newly described genus Eoconfuciusornis to the family. ^[5]

Biogeography

Most confuciusornithids are known from the upper Jehol group, the Yixian Formation and Jiufotang Formation, dating from 125 to 120 million years ago. Eoconfuciusornis, however, predated the other confuciusornithids by 6 million years, dating to 131 Ma ago.

Anatomy

The entire body of confuciusornithids was covered in contour feathers, except for the foot, base of beak, and the tarsometatarsus, the bone directly attached to the foot. ^[6] It appears that they may also have had down feathers. ^[6]

The beaks of confuciusornithids show development of modern birdlike characteristics, such as a large beak and lack of teeth. The premaxilla and dentary are larger than those of Archaeopteryx. ^[7] The anterior of these bones shows evidence of vasculature and innervation, implying the presence of a beak. ^[3] The lack of recovery of this structure indicates that the beak had a soft horny sheath. The softness of the beak along with the innervation suggest that the beak was sensitive, making it useful for searching for prey. ^[6]

Much of their anatomy resembles that of Archaeopteryx, especially the pectoral girdle and forelimbs. ^[7] They were better adapted for flight than Archaeopteryx, due to the elimination of two thoracic vertebrae. ^[7] The development of a pygostyle also shows better adaptation for flight, as this replaces the long tails present in earlier avialans. ^[3] Similarly to Archaeopteryx, confuciusornithids possessed a large first digit with a hook-like claw. The digit implies a climbing lifestyle, as it serves to allow for hooking onto the grooves of trees. A similar anatomy and function is seen in the nestlings of the hoatzin, an extant South American bird.

The biomechanics of the wing itself are quite contentious due to a combination of traits that imply different modes of flight. ^[8] Confuciusornithids possessed long primary feathers similar to those of modern fast-flapping birds, as opposed to gliding birds which have short primaries relative to their size. ^[8] However, the narrowness of the wings of confuciusornithids along with the lack of upstroke ability during flapping motion seem to preclude the ability to flap their wings quickly. ^[8] Thus, they may have relied upon a flight method that no longer exists in modern birds.

The hindlimbs of confuciusornithids did not resemble those of living birds. ^[6] They were bad runners, with feet curved in a way that implies they did not move on the ground.

The long feathers of the tail (central rectrices) of confuciusornithids are of disputed function. Sexual dimorphism is an explanation, with males presumed to use the feathers in mating displays. ^[9] However, it has been argued that the long rectrices were instead used as a defense against predators, as many birds shed feathers to protect themselves. The observation that less than 10% of confuciusornithid fossils possess these feathers supports this, as they may have been shed either in response to predators, or to the stress of the sudden death that produced the fossils. ^[9]

Paleoecology

Confuciusornithids were first thought to be herbivorous due to the lack of teeth. ^[6] However, their anatomy was not adapted for plant consumption, as gastroliths have never been found, nor did the weak rhamphotheca of the beak allow for grinding. Instead, the beak appears to have been sensitive enough to assist in food acquisition and capable of holding potential prey. This beak type is well suited for skimming prey off of the top of a body of water. ^[6] Large numbers of fossils appear to originate from the tops of freshwater lakes, further supporting the water feeding connection. The remains of fish have been found in fossils of C. sanctus. ^[10] Confuciusornithids appear to have been unable to take off from water and lacked the adaptations necessary to live aquatically. ^[6] Thus, it appears that they flew along the surface of the water, using their beak to search for fish.

Confuciusornithid remains have been found in the abdominal contents of Sinocalliopteryx gigas, a compsognathid predator. ^[11] Multiple confuciusornithids were present in the remains, implying that they were all captured in a short time. ^[11]

Confuciusornithids appear to have been social animals, as concurrently buried fossils are often found in close proximity. ^[6]

Reproduction

A 2018 study suggests that confuciusornithids could not have incubated their eggs like modern birds do. ^[12] Other paravians (including Deinonychus ) and pterosaurs are known to be superprecocial and able to fly soon after birth, ^{[13] [14] [15]} but for now there are no unambiguous confuciusornithid juveniles to attest this.

Related Research Articles

Confuciusornis is a genus of basal crow-sized avialan from the Early Cretaceous Period of the Yixian and Jiufotang Formations of China, dating from 125 to 120 million years ago. Like modern birds, Confuciusornis had a toothless beak, but closer and later relatives of modern birds such as Hesperornis and Ichthyornis were toothed, indicating that the loss of teeth occurred convergently in Confuciusornis and living birds. It was thought to be the oldest known bird to have a beak, though this title now belongs to an earlier relative Eoconfuciusornis. It was named after the Chinese moral philosopher Confucius. Confuciusornis is one of the most abundant vertebrates found in the Yixian Formation, and several hundred complete specimens have been found.

The Enantiornithes, also known as enantiornithines or enantiornitheans in literature, are a group of extinct avialans, the most abundant and diverse group known from the Mesozoic era. Almost all retained teeth and clawed fingers on each wing, but otherwise looked much like modern birds externally. Over eighty species of Enantiornithes have been named, but some names represent only single bones, so it is likely that not all are valid. The Enantiornithes became extinct at the Cretaceous–Paleogene boundary, along with Hesperornithes and all other non-avian dinosaurs.

Pygostyle describes a skeletal condition in which the final few caudal vertebrae are fused into a single ossification, supporting the tail feathers and musculature. In modern birds, the rectrices attach to these. The pygostyle is the main component of the uropygium, a structure colloquially known as the bishop's nose, parson's nose, pope's nose, or sultan's nose. This is the fleshy protuberance visible at the posterior end of a bird that has been dressed for cooking. It has a swollen appearance because it also contains the uropygial gland that produces preen oil.

Jinfengopteryx is a genus of maniraptoran dinosaur. It was found in the Qiaotou Member of the Huajiying Formation of Hebei Province, China, and is therefore of uncertain age. The Qiaotou Member may correlate with the more well-known Early Cretaceous Yixian Formation, and so probably dates to around 122 Ma ago.

The evolution of birds began in the Jurassic Period, with the earliest birds derived from a clade of theropod dinosaurs named Paraves. Birds are categorized as a biological class, Aves. For more than a century, the small theropod dinosaur Archaeopteryx lithographica from the Late Jurassic period was considered to have been the earliest bird. Modern phylogenies place birds in the dinosaur clade Theropoda. According to the current consensus, Aves and a sister group, the order Crocodilia, together are the sole living members of an unranked reptile clade, the Archosauria. Four distinct lineages of bird survived the Cretaceous–Paleogene extinction event 66 million years ago, giving rise to ostriches and relatives (Palaeognathae), waterfowl (Anseriformes), ground-living fowl (Galliformes), and "modern birds" (Neoaves).

Jeholornis is a genus of avialan dinosaurs that lived between approximately 122 and 120 million years ago during the early Cretaceous Period in China. Fossil Jeholornis were first discovered in the Jiufotang Formation in Hebei Province, China and additional specimens have been found in the older Yixian Formation.

Yandangornis is a genus of theropods from the Late Cretaceous Tangshang Formation of China. It lived 81.5 million years ago in what is now China. The type species, Y. longicaudus, was formally described by Cai and Zhou in 1999.

Sapeornis is a monotypic genus of avialan dinosaurs which lived during the early Cretaceous period. Sapeornis contains only one species, Sapeornis chaoyangensis.

Avialae is a clade containing the only living dinosaurs, the birds, and their closest relatives. It is usually defined as all theropod dinosaurs more closely related to birds (Aves) than to deinonychosaurs, though alternative definitions are occasionally used.

Paraves are a widespread group of theropod dinosaurs that originated in the Middle Jurassic period. In addition to the extinct dromaeosaurids, troodontids, anchiornithids, and possibly the scansoriopterygids, the group also contains the avialans, which include diverse extinct taxa as well as the over 10,000 species of living birds. Basal members of Paraves are well known for the possession of an enlarged claw on the second digit of the foot, which was held off the ground when walking in some species. A number of differing scientific interpretations of the relationships between paravian taxa exist. New fossil discoveries and analyses make the classification of Paraves an active subject of research.

Eoalulavis is a monotypic genus of enantiornithean bird that lived during the Barremian, in the Lower Cretaceous around 125 million years ago. The only known species is Eoalulavis hoyasi.

Yixianornis is a bird genus from the early Cretaceous period. Its remains have been found in the Jiufotang Formation at Chaoyang dated to the early Aptian age, around 120 million years ago. Only one species, Yixianornis grabaui, is known at present. The specific name, grabaui, is named after American paleontologist Amadeus William Grabau, who surveyed China in the early 20th century.

Changchengornis is an extinct basal pygostylian genus from the Early Cretaceous. Its remains have been found in the People's Republic of China, in Chaomidianzi Formation rocks from around the Barremian-Aptian boundary, deposited 125 million years ago. Changchengornis was a close relative of the better-known Confuciusornis. In 1999 it was assigned to the Confuciusornithidae.

Pygostylia is a group of avialans which includes the Confuciusornithidae and all of the more advanced species, the Ornithothoraces.

Zhongornis is a genus of primitive maniraptoran dinosaurs that lived during the Early Cretaceous. It was found in rocks of the Yixian Formation in Lingyuan City (China), and described by Gao et al. in 2008.

Eoconfuciusornis a genus of extinct avialan that lived 131 Ma ago, in the Early Cretaceous of China. It is the oldest known bird to have a beak.

Anchiornis is a genus of small, four-winged paravian dinosaurs, with only one known species, the type species Anchiornis huxleyi, named for its similarity to modern birds. The Latin name Anchiornis derives from a Greek word meaning "near bird", and huxleyi refers to Thomas Henry Huxley, a contemporary of Charles Darwin.

Shanweiniao is a genus of long-snouted enantiornithean birds from Early Cretaceous China. One species is known, Shanweiniao cooperorum. There is one known fossil, a slab and counterslab. The fossil is in the collection of the Dalian Natural History Museum, and has accession number DNHM D1878/1 and DNHM1878/2. It was collected from the Lower Cretaceous Dawangzhengzi Beds, middle Yixian Formation, from Lingyuan in the Liaoning Province, China.

The Archaeornithes, classically Archæornithes, is an extinct group of the first primitive, reptile-like birds. It is an evolutionary grade of transitional fossils, the primitive birds halfway between non avian dinosaur ancestors and the derived modern birds.

Euornithes is a natural group which includes the most recent common ancestor of all avialans closer to modern birds than to Sinornis.

References