Confuciusornis

Confuciusornis is a genus of primitive crow-sized bird 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 close 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 is the oldest known bird to have a beak. It was named after the Chinese moral philosopher Confucius (551–479 BC). Confuciusornis is one of the most abundant vertebrates found in the Yixian Formation, and several hundred complete, articulated specimens have been found. In November 1993, the Chinese paleontologists Hou Lianhai and Hu Yoaming, of the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) at Beijing, visited fossil collector Zhang He at his home in Jinzhou, where he showed them a fossil bird specimen that he had bought at a local flea market. In December, Hou learned about a second specimen, which had been discovered by farmer Yang Yushan. Both specimens stem from the same locality in Shangyuan, Beipiao. In 1995, these two specimens as well as a third one were formally described as a new genus and species of bird, Confuciusornis sanctus, by Hou and colleagues. The generic name combines the philosopher Confucius with a Greek ὄρνις, (ornis), 'bird'. The specific name means 'holy one' in Latin and is a translation of Chinese 圣贤, shèngxián, 'sage', again in reference to Confucius. The first discovered specimen was designated the holotype and catalogued under the specimen number IVPP V10918; it comprises a partial skeleton with skull and parts of the forelimb. Of the other two skeletons, one (paratype, IVPP V10895) comprises a complete pelvis and hind limb, and the other (paratype, IVPP V10919–10925) a fragmentary hind limb together with six feather impressions attached to both sides of the tibia (shin bone). It was soon noted that the two paratype specimens only comprise bones that are unknown from the holotype, and that this lack of overlap makes their referral to the species speculative. Only the discovery of a plethora of well-preserved specimens shortly after had confirmed that the specimens indeed represent a single species.:16 Together with the early mammal Zhangheotherium, which was discovered at around the same time, Confuciusornis was considered the most remarkable fossil discovery of the Jehol biota, which in the next decades would reveal the most important record of Mesozoic birds worldwide.:5–6 In the late 1990s, Confuciusornis was considered both the oldest beaked bird as well as the most primitive bird after Archaeopteryx. It was also considered to be only slightly younger than Archaeopteryx – the Yixian Formation, the rock unit where most Confuciusornis specimens have been found, was thought to be of Late Jurassic (Tithonian) age at the time. Although two bird genera, Sinornis and Cathayornis, had already described from the Jehol biota in 1992, these were only based on fragmentary remains and stem from the younger Jiufotang Formation, which was considered to be of Early Cretaceous age. Later, both formations have been dated to the Lower Cretaceous (Barremian to Aptian stages, 131–120 million years ago). In 1995, local farmers began digging for fossils near the village of Sihetun, Beipiao, in what would become one of the most productive localities of the Jehol biota. Large-scale professional excavations at this single locality have been carried out by the IVPP from 1997 onwards; recovered fossils include several hundred specimens of Confuciusornis. Many additional sites producing fossils of the Jehol biota have been recognized since, distributed over a large region including Liaoning, Hebei, and Inner Mongolia.:7 Due to the great abundance, preservation, and commercial value of the fossils, excavations by local farmers produced an unusually high number of fossils. Although a portion of these fossils have been added to the collections of Chinese research institutions, more have probably been smuggled out of the country. In 1999, it was estimated that the National Geological Museum of China in Beijing housed nearly 100 specimens of Confuciusornis,:16 and in 2010, the Shandong Tianyu Museum of Nature was reported to possess 536 specimens of the bird. The majority of specimens, however, are held privately and thus are not available for research. At one time forty individuals were discovered on a surface of about 100 m2. This has been explained as the result of entire flocks of birds being simultaneously killed by ash, heat or poisonous gas following the volcanic eruptions that caused the tuff stone in which the fossils were found to be deposited as lake sediments. Since the description of Confuciusornis sanctus, five additional species have been formally named and described. As with many other fossil genera, species are difficult to define, as differences between species can often not be readily distinguished from variation that occurs within a species.:50 In the case of Confuciusornis, only C. sanctus is universally accepted. In 2002 Hou named the genus Jinzhouornis, but Chiappe et al. (2018) and Wang et al. (2018) showed that this genus is a junior synonym of Confuciusornis based on morphometry and examination of known confuciusornithiform specimens. Confuciusornis was about the size of a modern pigeon, with a total length of 50 centimetres (1.6 feet) and a wingspan of up to 70 cm (2.3 ft). Its body weight has been estimated to have been as much as 1.5 kilograms (3.3 lb), or less than 0.2 kg (0.44 lb). C. feducciai was about a third longer than average specimens of C. sanctus.