| Hongshanornis Temporal range: Early Cretaceous, 124.6 Ma |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| clade: | Ornithurae |
| Family: | †Hongshanornithidae |
| Genus: | †Hongshanornis Zhou & Zhang, 2005 |
| Species: | †H. longicresta Zhou & Zhang, 2005 |
Hongshanornis is a genus of ornithurine bird known from the early Cretaceous lake deposits of the Yixian Formation, Inner Mongolia, China. The only known specimen (an adult with fully preserved plumage) was recovered in 2005. It was likely a strong flier and due to its long legs, Hongshanornis appears to have been a wader, feeding in the shallows of lakes. The holotype specimen is currently held by the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing.
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The teeth are very reduced and were not preserved in the only known specimen. At first, this led scientists to conclude that the teeth were absent in both the upper and lower jaws, probably replaced with a beak, which would represent the earliest known beaked ornithurine bird. However, later study of the specimen showed that tooth sockets were present in the preserved parts of the jaw, and comparison with related forms showed that it did have teeth and probably lacked a beak.[1]
The describers of Hongshanornis noted a unique bone in the end of the lower jaw which they equated with the beak-bearing predentary bone in ornithischian dinosaurs. Such bones have also been found in more advanced birds like Hesperornis. The authors said, "the preservation of a predentary bone confirms that this structure is not unique to ornithischian dinosaurs, but was common in early ornithurine birds."[2] However, other scientists later cast doubt on this interpretation, arguing that there is no evidence linking the structure in ornithurines with the one in ornithischians. They also pointed out that the supposed predentary of Hongshanornis lacks the characteristic pits and grooves associated with the beak in true early beaked birds, and that the presence of any beak is doubtful.[1]
The describers of Hongshanornis noted the apparent presence of a large feathered crest on the head,[2] though the feather traces are extremely poor quality and it may be an artifact of preservation.[1]
Hongshanornis is normally classified as an ornithurine or ornithuromorph, a fairly advanced lineage of short-tailed birds. Howeve,r some features are so primitive that some researchers have suggested it belongs to a more primitive lineage of short-tailed birds (pygostylians). However, the validity of the clade uniting the short-tailed bird groups Enantiornithes, Ornithurae, and more basal birds such as Confuciusornis is increasingly viewed as suspect, with half of the few supposedly unique pygostylian traits — including the pygostyle itself — now known or strongly suspected to be homoplasies.[3]
