Confuciusornis

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A long- and a short-tailed Confuciusornis in flight, showing the strange wing shape (drawing by F. Spindler)

Confuciusornis is a genus of crow-sized prehistoric bird from the Early Cretaceous of China, approximately 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.

Recognized species are C. sanctus (the type species), C. dui, C. chuonzhous and C. suniae (the latter two being possibly synonymous with C. sanctus). A close relative, Changchengornis hengdaoziensis lived in the same time and region. Changchengornis also possessed the long tail feathers, as well as a noticeable downy coat of feathers. Recent cladistic analyses suggest that Confuciusornis may be more closely related to Microraptor and other dromaeosaurs than to Archaeopteryx (Mayr et. al, 2005); in any case, it was certainly not derived from Archaeopteryx.

Fossils of Confuciusornis show that it had an exceptionally large humerus. A characteristic hole near its shoulder-end may have reduced the bone's weight. The furcula or wishbone was a simple bar, like that of Archaeopteryx. The sternum was a small and simple plate that may have had a slight keel but was otherwise unsuitable for the attachment of large muscles. However, the scapulas were fused to the coracoid bones and may have formed a solid base for the attachment of flight muscles. No modern bird has a comparable structure. The orientation of the glenoid (shoulder) joint was sideways, instead of angled dorsally as in modern birds; this means that Confuciornis was unable to lift its wings above its back. Like Archaeopteryx, it was thus incapable of the upstroke required for modern flapping flight (Senter, 2006), but the peculiar shoulder bones make it possible that it may have used another technique.

Confuciusornis is more advanced than Archaeopteryx in possessing a short tail with a pygostyle (a bone formed from a series of short, fused tail vertebrae), but more primitive than modern birds in retaining large claws on the forelimbs. The primary remiges are more than twice the length of the hand and relatively longer than those of any living bird, while the secondary remiges were rather short by comparison. Thus, the wing shape was very unlike that of living birds. Many individuals show long, streamer-like tail feathers that may indicate sexual dimorphism and could have been used in courtship, but the rest of the tail feathers were small and probably of little use in flight. The proportions of the toes suggest that they were used for both walking and climbing, while the large claws of the thumb and third finger were probably used for climbing. The head probably had a small crest or tuft similar to that in today's mousebirds or turacos.

There are immature specimens known, and from the analysis of bone growth patterns of young adults it has been estimated that Confuciusornis reached maturity somewhat slower than extant small birds, but faster than advanced dinosaurs (de Ricqlès et al., 2003), which might indicate an omnivorous diet similar to modern crows.

It has been hypothesized that Confuciusornis fed on plant materials due to its toothless beak (Zhou & Zhang, 2003). One specimen (IVPP V133) with apparent fossilized food remains has been recovered to date; it seems to have been in the process of regurgiating a pellet of fish bones (probably Jinanichthys) when it died (Dalsätt et al., 2006).

[edit] References

• Dalsätt, J.; Zhou, Z.; Zhang, F. & Ericson, Per G. P. (2006). Food remains in Confuciusornis sanctus suggest a fish diet. Naturwissenschaften 93(9): 444–446. DOI:10.1007/s00114-006-0125-y (HTML abstract)

• Hou, L.; Zhou, Z.; Gu, Y. & Zhang, H. (1995). [Description of Confuciusornis sanctus]. Chinese Science Bulletin 10: 61-63.

• Hou, L.-H.; Zhou, Z.; Martin, L.D. & Feduccia, A. (1995): A beaked bird from the Jurassic of China. Nature 377: 616-618. DOI:10.1038/377616a0 (HTML abstract)

• de Ricqlès, A.J.; Padian, K.; Horner, J.R.; Lamm, E.-T. & Myhrvold, N. (2003): Osteohistology of Confuciusornis sanctus (Theropoda: Aves). Journal of Vertebrate Paleontology 23(2): 373–386. DOI:10.1671/0272-4634(2003)023[0373:OOCSTA]2.0.CO;2 HTML abstract

• Mayr, G.; Pohl, B. & Peters, D. S. (2005). A well-preserved Archaeopteryx specimen with theropod features. Science 310(5753): 1483-1486. DOI:10.1126/science.1120331 (HTML abstract) Supporting Online Material

• Senter, Phil (2006): Scapular orientation in theropods and basal birds, and the origin of flapping flight. Acta Palaeontologica Polonica 51(2): 305–313. PDF fulltext

• Zhou, Z. & Zhang, F. (2003): Jeholornis compared to Archaeopteryx, with a new understanding of the earliest avian evolution. Naturwissenschaften 90: 220–225. PDF fulltext