In Depth
Confuciusornis is a genus of early bird that lived in China during the early Cretaceous. The interesting thing about the genus though is that even though it is clearly a primitive bird, it just doesn’t seem to quite fit within the established evolutionary transition of birds.
The first birds appeared at least as far back as the Tithonian of the Jurassic roughly around twenty to twenty-seven million years before the known appearance of Confuciusornis in the fossil record. The obvious reference here is the appearance of Archaeopteryx in what would become Europe, and although a new genus of primitive bird may one day be discovered to have lived before Archaeopteryx, Archaeopteryx is the genus that is still currently used to compare other primitive birds to, partially at least because of the wealth of study that has been devoted to Archaeopteryx.
The most primitive birds were recently descended from theropod dinosaurs, and they still had long thin theropod-like tails, a feature that is firmly established as present in Archaeopteryx. In Confuciusornis the tail has already disappeared and has been replaced by a pygostyle like those of modern birds. The pygostyle in modern forms is where the flight tail feathers that control steering and drag during flight are attached to the body, but even though Confuciusornis had a pygostyle, no tail flight feathers were present.
Instead of flight feathers, the pygostyle had a covering of more simply downy contour feathers. There were however two exceptionally long feathers that trailed behind the body in some specimens. These have been described to have been more like ribbons in that they were only reinforced with a central spine at the ends rather than the full length of the feather. Because these two feathers are only known in some specimens, they have been speculated to have been display features that were used by the males to attract females.
Although living during the early Cretaceous, Confuciusornis already had well developed flight feathers on the wing, and with the longest measuring up to 207 millimetres in length, Confuciusornis had some of the proportionately longest flight feathers relative to body size known for any bird, including modern forms. In 2010 a study led by Zhang Fucheng et al, investigated the colouration of Confuciusornis feathers by scanning them under an electron microscope and searching for the melanosomes. During their search, Confuciusornis specimen IVPP 13171 yielded melanosomes that indicated colours of grey, black and either red or brown.
The colours for Confuciusornis certainly fall within the known spectrum for early bird and dinosaur colours. Archaeopteryx is known to have had some black feathers on the wings, and the feathered dinosaur Sinosauropteryx is known to have had an alternating pattern of brown and white bands that ran down the length of the tail. Best known so far is Anchiornis which has been confirmed to have been black all over with white streaks down the wings, red speckling on the face and an orange feathered crest on top of the head.
At first glance the wings of Confuciusornis seem to be very well adapted for flight, they are certainly among the longest wings relative to body size so far known in primitive birds. The humerus (equivalent to your upper arm bone) is long and has a large opening that not only reduced weight, but may have allowed for the attachment of larger and hence more powerful muscles. The second and third metacarpals (equivalent to your hand bones) were partially fused, while the second metacarpal was also more heavily built for supporting the flight feathers. The fingers on Confuciusornis could still move independently from one another, and claws grew from the ends. The claw of the first digit was also larger than the claws of the second and third digits. One feature of modern birds that was lacking in Confuciusornis was the alula, more commonly referred to as the ‘bastard wing’. The alula is essentially a small extension of the wing that projects from the front (anterior) edge. The alula is formed by the growth of several flight feathers that are anchored to the first digit. In normal forward flight the alula folds along the edge of the wing, but when slower speeds are required, such as when landing, the alula is extended to provide additional lift so that the bird does not stall in the air and fall to the ground.
The lack of an alula indicates that Confuciusornis were not agile slow speed fliers, and probably could not slow themselves down all that much for landing. This might explain the reason for having possibly more powerful muscles as these might have allowed the wings to absorb some of the impact of landing. This may have been a case of flying from tree trunk to tree trunk since the claws of the fingers, particularly the first would have been an additional aid in gripping the trunks.
There is little doubt that Confuciusornis could fly, but how well remains a matter of strong debate. The wings and flight feathers on them were easily capable of providing lift, but the real question is could Confuciusornis go beyond gliding and use these wings for powered flapping flight? Gliding is easy to establish, and many consider gliding habits either for moving through a habitat or predator escape to be the precursor to flapping flight. To look at the possibility of flapping flight, the wings are important but you must also think about the rest of the skeleton.
One key development that allows for flapping flight is the ability to perform an efficient flight stroke, a motion of wing movement that allows the wings to lift the body into the air and keep it there. Modern birds have shoulders aligned dorsally and angled slightly upwards to the back so that the wings can arc up above the back for a stronger flight stroke. In Confuciusornis however the shoulders attach further down and have a sideways orientation that likely prevented them from lifting above the head.
Flapping wings also need powerful muscles, but not so much in the wings themselves but across the chest. Analogous to your own pectoral muscles, these muscles provide the bulk of the power for flapping flight and are exactly why birds have deep, round chests. These muscles however need strong attachment points to connect them to the skeleton. This is usually a sternum (breast bone) that has a developed bony keel to provide a larger surface area for muscle attachment. In Confuciusornis the keel was present, but is not seen to have been as well developed as the keels of modern bird forms, something that counts against the ability for Confuciusornis to be a strong powered flyer. Often in modern birds the bony keel is further extended by a cartilaginous addition, something that you can see for yourself when you carve up a chicken. Cartilage does not tend to fossilise because it is still soft tissue that usually decays before it can be fossilised, though impressions of cartilage can sometimes be preserved. However, despite the hundreds of Confuciusornis specimens so far discovered, an impression of a cartilaginous keel has yet to be positively identified.
Sharing some of the same problems as Archaeopteryx, Confuciusornis does not seem to have had entirely the necessary requirements to rely upon flapping flight. The lack of flight feathers on the tail as well as the lack of an alula also indicate that when in the air, Confuciusornis would not have had anything like the manoeuvrability of modern birds, and in this respect these could be further arguments against powered flight. But just maybe we should not be so concerned about comparing primitive forms to modern birds. Confuciusornis was a primitive bird, always was and will be, so it would be foolhardy to say it could not do certain things just because it lacked some features that modern birds use thanks to an additional one hundred and twenty million years of evolution. One key fact to consider is that Confuciusornis is known by hundreds of specimens, and the overwhelming majority of these were preserved in lake sediments. This of course leads to another question, if Confuciusornis couldn’t fly, then how did so many end up at the bottom of a lake? The areas where Confuciusornis are known from are known to have been geologically active (volcanoes, earthquakes, etc) and it has been proposed more than once that the accumulation of so many Confuciusornis at the bottom of a lake could have been the result of flocks of Confuciusornis getting caught in sudden releases of volcanic gases and/or ash as they flew over the lake.
An additional thing to think about is that because lakes are large open bodies of water they tend to lack features that can slow down wind, meaning stronger gusts of air over the water surface. You can feel this effect for yourself just by walking next to a large body of water whether it is a natural lake, reservoir or water filled gravel pit. If Confuciusornis frequented lakeside environments then they may have had a third option; soaring. Like gliding, soaring does not require that much wing movement beyond fairly minor adjustments to take advantage of wind currents, and beyond the initial lift into the air, flapping may not have even been required. The lack of tail flight feathers would have course been a hindrance to fine flight control, but maybe Confuciusornis relied more upon the actual wings for steering. This would also explain the possible presence of stronger muscles within the wings themselves as they would compensate for a lack of tail. This would be analogous to flying an aeroplane just by the ailerons of the wings rather than the elevons and rudder of the tail as well.
Another area of confusion is that Confuciusornis had a toothless beak. Compared to modern birds this is not that unusual at all, but some Cretaceous era birds such as Ichthyornis and Hesperornis which lived much later than Confuciusornis are known to still have strongly developed teeth. However, Ichthyornis and Hesperornis are probably not good examples to compare Confuciusornis too as both of these genera were sea birds and piscivores (fish eaters), and the teeth would have been a useful adaptation in spearing the bodies of fish. With that said though, modern fish eating birds have toothless beaks as well, though some such as Mergus merganser (also known as the Goosander and Common Merganser) have a serrated edge to their beaks.
The loss of teeth in Confuciusornis could just be down to a feeding specialisation or even a generalisation, and that forms such as Ichthyornis and Hesperornis retained their teeth later simply because they fitted their feeding lifestyle better. The exact diet of Confuciusornis is unknown, but a bolus of fish bones believed to have been from the genus Jinanichthys have been found as what could be stomach remains of a specimen of Confuciusornis (IVPP V13313). This would indicate that Confuciusornis could take and consume small fish, and coupled with the occurrence of so many Confuciusornis specimens in connection with lake sediments, it seems that piscivory is highly likely in Confuciusornis. This does not necessarily mean that Confuciusornis were exclusive piscivores however as there are a few modern birds such as Tanysiptera (paradise kingfisher) which are known to eat fish, but will also hunt for other creatures too. On an additional note, Tanysiptera also have tail plumes similar to those of Confuciusornis.
While Confuciusornis is one of the first birds known to have had a beak, the beak itself was still quite primitive. Aside from being heavily built, the upper beak was also incapable of moving, while in modern birds the snout can move slightly so that the mouth can be opened wider. The beaks of Confuciusornis can illustrate a stage of how beaks not only came to be formed, but a stage in the development of this feature. The development of beaks and toothlessness is not exclusive to birds however, some groups of theropod dinosaurs are also known to have developed beaks, with the oviraptosaurs being the best known group. The ornithomimosaurs and the therizinosaurs are two more examples of theropod dinosaurs that became toothless with time.
Rather than having a firm placement in the on-going evolution of birds, Confuciusornis might represent an evolutionary offshoot that developed some features that were similar to later birds, but otherwise did not have any descendants that went anywhere with them. This would at least explain the mix of primitive and modern features that appeared before they became standardised in later forms. Here the driving force would have been convergent evolution, where an organism adapts to a specific set of survival parameters that other unrelated creatures also have to live to, hence the appearance of similar adaptations. The concept of ‘evolutionary dead ends’ is well known, and if true, then Confuciusornis would not be the only example of an evolutionary off shoot that just didn’t go anywhere.
Further Reading
- Confuciusornis sanctus, a new Late Jurassic sauriurine bird from China - L. Hou, Z. Zhou, Y. Gu, H. Zhang - 1995. - The discovery of Early Cretaceous birds in China - Z. Zhou - 1995. - Confuciusornis sanctus compared to Archaeopteryx lithographica - L. D. Martin, Z. Zhou, L. Hou & A. Feduccia - 1998. - Osteological microstructure of Confuciusornis: preliminary report - F. Zhang, L. Hou & L. Ouyang - 1998. - Confuciusornis and the early evolution of birds - Z. Zhou & L. Hou - 1998. - Some microstructure difference among Confuciusornis, Alligator and a small theropod dinosaur, and its implications - F. -C. Zhang, X. Xu & J. L� - 1999. - A diapsid skull in a new species of the primitive bird Confuciusornis - L. Hou, L. D. Martin, Z. Zhou, A. Feduccia & F. Zhang - 1999. – Anatomy and systematics of the Confuciusornithidae (Theropoda: Aves) from the late Mesozoic of northeastern China – Luis M. Chiappe, Ji Shu-An. Ji Qiang & Mark A. Norell – 1999. – Taphonomy and mass mortality of Confuciusornis and feathered dinosaurs at the Sihetun and Zhangjiagou sites in western Liaoning, China – X. Wang, F. Zhang, X. Xu, Y. Wang & G.Gu – 2000. - New advances in the study of the primitive bird Confuciusornis - Q. Ji - 2001. - ‘Flight capability and habits of Confuciusornis’. In: Gauthier and Gall (eds). New perspectives on the origin and early evolution of birds: proceedings of the international symposium in honor of John H. Ostrom - Z. Zhou & J. O. Farlow - 2001. - Biology of basal birds and the origin of avian flight”. In: Zhou Z., Zhang F. (eds) - A. Elzanowski - 2002. - Osteohistology of Confuciusornis sanctus (Theropoda: Aves) - A. J. De Ricql�s, K. Padian, J. R. Horner, E. T. Alamm & N. Myhrvold - 2003. - Development and evolution of avian racket plumes: Fine structure and serial homology of the wire - Robert Bleiwess - 2005. - Non-Avian dinosaur fossils from the Lower Cretaceous Jehol Group of western Liaoning, China - X. Xu & M. A. Norell - 2006. - Life history of a basal bird: morphometrics of the Early Cretaceous Confuciusornis - L. M. Chiappe, J. Marugan-Lobon, S. Ji & Z. Zhou - 2008. - Diversification in an Early Cretaceous avian genus: evidence from a new species of Confuciusornis from China - Z. Zhang, C. Gao, Q. Meng, J. Liu, L. Hou & G. Zheng - 2009. - An attempt to reconstruct the lifestyle of confuciusornithids (Aves, Confuciusornithiformes) - A. V. Zinoviev - 2009. - Life history, sexual dimorphism and ‘ornamental’ feathers in the mesozoic bird Confuciusornis sanctus - Winfried S. Peters & Dieter Stefan Peters - 2009. - Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds - Fucheng Zhang, Stuart L. Kearns, Patrick J. Orr, Michael J. Benton, Zhonghe Zhou, Diane Johnson, Xing Xu & Xiaolin Wang - 2010. - [A new species of Confuciusornis from Lower Cretaceous of Jianchung, Liaoning, China] - L. Li, J.-Q. Wang & S.-L. Hou - 2010. - Narrow primary feather rachises in Confuciusornis and Archaeopteryx suggest poor flight ability - R. L. Nudds & G. J Dyke - 2010. - Comment on ‘Narrow Primary Feather Rachises in Confuciusornis and Archaeopteryx Suggest Poor Flight Ability - Gregory S. Paul - 2010. - Basal birds from China: a brief review - D. Li, C. Sulliven, Z. Zhou & Z. Zhang - 2010. - Comment on “Narrow Primary Feather Rachises in Confuciusornis and Archaeopteryx Suggest Poor Flight Ability - Xiaoting Zheng, Xing Xu, Zhonghe Zhou, Desui Miao & Fucheng Zhang - 2010. - Response to comments on “Narrow Primary Feather Rachises in Confuciusornis and Archaepteryx Suggest Poor Flight Ability - R. L. Nudds & G. Dyke - 2010. - Nocturnality in Dinosaurs Inferred from Scleral Ring and Orbit Morphology - L. Schmitz & R. Motani - 2011. - Gender identification of the Mesozoic bird Confuciusornis sanctus - A. Chinsamy, L. M. Chiappe, J. S. Marug�n-Lob�n, G. Chunling, Z. Fengjiao - 2013. – Laser Fluorescence Illuminates the Soft Tissue and Life Habits of the Early Cretaceous Bird Confuciusornis. – PLOS ONE. 11 (12). – A. R. Falk, T. G. Kaye, Z. Zhou & D. A. Burnham – 2016. – Elaborate plumage patterning in a Cretaceous bird. – PeerJ. 6. – Quanguo Li, Julia A. Clarke, Ke-Qin Gao, Jennifer A. Peteya & Matthew D. Shawkey – 2018.- A new confuciusornithid bird with a secondary epiphyseal ossification reveals phylogenetic changes in confuciusornithid flight mode. – Communications Biology. 5. 1398. – Renfei Wang, Dongyu Hu, Meisheng Zhang, Shiying Wang, Qi Zhao, Corwin Sullivan & Xing Xu – 2022.
