| Zhongornis | |
|---|---|
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Genus: | †Zhongornis Gaoet al., 2008 |
| Species: | †Z. haoae |
| Binomial name | |
| †Zhongornis haoae Gaoet al., 2008 | |
Zhongornis (meaning "intermediate bird"[1]) is a genus of primitivemaniraptorandinosaurs that lived during the Early Cretaceous. It was found in rocks of theYixian Formation inLingyuan City (China), and described by Gao et al. in 2008.[2]
Zhongornis has only one described species,Zhongornis haoae. The only specimen is a fossil slab and counterslab numbered D2455/6. It is in the collection of the Dalian Natural History Museum. It is a fairly complete skeleton about eight centimeters in length. Pores in the bones and unfused sutures in the skeleton indicate that the specimen was a juvenile, but the authors believe that it was developed enough to erect a newtaxon on the basis of its unique morphological characters. There are feather impressions preserved on the right hand and also probable tail feathers preserved near the left foot.Zhongornis had a beaked mouth with no teeth. The tail is proportionately short, has thirteenvertebrae, and no pygostyle. The third finger has only two phalangeal bones, unlike non-avian dinosaurs andConfuciusornis, and more likeEnantiornithes and more advanced avialans. These features and a cladistic analysis indicate thatZhongornis is the sister group to allpygostylia, meaning that it is intermediate between long-tailedAvialae, likeArchaeopteryx, and more advanced taxa, likeConfuciusornis.
Zhongornis provides important anatomical information about the evolutionary transition from primitive basal Avialae likeArchaeopteryx, which had a long bony tail and a dinosaur-like third finger, to the more advanced avialans like theEnantiornithes, which had reduced third fingers and tails fused into rigidpygostyles.Zhonghornis is the only fossil ever found that seems to be intermediate in these features. It appears to have one less bone in the third finger thanArchaeopteryx, and one more thanLongipteryx, suggesting that it is an intermediate between the two.[2]Zhongornis also seems to be intermediate in its tail anatomy. It has only thirteencaudal vertebrae, far less than the 22 inArchaeopteryx. None of the vertebral centra are fused, but the last four do form a continuous lateral flange, implying that this specimen had an incipient pygostyle. Previous to this fossil Sanz et al. (1992) suggested that the evolution of the pygostyle may have proceeded as the numerous vertebrae of the tail became very small and highly ankylosed.[3]Zhongornis suggests that shortening of the tail, and a large reduction in the number of vertebrae, preceded the origin of the pygostyle in the evolution of at least one bird language.
After a detailed restudy, O'Connor and Sullivan suggest that this juvenile bird from the Early Cretaceous Jehol fauna of China actually possesses 20, rather than 14, tail vertebrae; further, this tail is very similar to those ofEpidexipteryx (a scansoriopterygid) andCaudipteryx (an oviraptorosaur). Based on this and other features, the authors reinterpretedZhongornis as the sister taxon of scansoriopterygids, and further suggested that this clade (Zhongornis +Scansoriopterygidae) is the sister group ofOviraptorosauria.[4] Other phylogenetic analyses, including a larger dataset, don't consider the hypothesis thatZhongornis is a scansoriopterygid, instead finding it in its traditional position as a primitive relative of pygostylians, or as a close relative ofConfuciusornis.[5] Some researchers consider the scansoriopterygid hypothesis invalid, as they believeZhongornis strongly differs from this group in many traits, traits that it also shares with birds.[6]
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