| Sapeornis | |
|---|---|
 | |
| Fossil specimen,National Museum of Natural Science | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Order: | †Omnivoropterygiformes |
| Family: | †Omnivoropterygidae |
| Genus: | †Sapeornis Zhou &Zhang, 2002 |
| Species: | †S. chaoyangensis |
| Binomial name | |
| †Sapeornis chaoyangensis Zhou & Zhang, 2002 | |
| Synonyms | |
Genus synonymy
Species synonymy
| |
Sapeornis is a monotypic genus ofavialandinosaurs which lived during the earlyCretaceous period (late Barremian to earlyAptian, roughly 125-120mya).Sapeornis contains only one species,Sapeornis chaoyangensis.
Sapeornis was large for an early avialan, about 30–33 centimetres (0.98–1.08 ft) long in life, excluding the tail feathers.
The hand ofSapeornis was far more derived than that ofArchaeopteryx. It had three fingers, the outer ones with two and the middle one with threephalanges, and a well-fusedcarpometacarpus. Its arms were about half again as long as the legs, suggesting a large wing area. On the other hand, its shoulder girdle was apparently ill-adapted to flapping flight and itsfurcula was unusual, with ahypocleidum similar to more advanced avialans but a general anatomy even more basal than inArchaeopteryx.[2] Thehumerus was large and bore holes, apparently to save weight, as in theConfuciusornithidae.
The skull has a handful of teeth in the upper jawtip only.Sapeornis hadgastralia but no (or unossified)uncinate processes. The breastbone (sternum) was either absent or, more likely, made of cartilage rather than bone, as in more basal theropods.[3] Thepygostyle was rod-like as inConfuciusornis andNomingia, but like in the former there was no long bony tail anymore. While thetarsometatarsi were more fused than inArchaeopteryx, thefibula was long and reached the distal point of the tarsal joint, not reduced as in more modern birds (and some non-avian theropods likeAvimimus). The first toe pointed backwards. In specimenIVPP V12375, the stomach contained numerous smallgastroliths. Analysis of its skeletal bones suggest that it had anontogeny and slow growth likeArchaeopteryx and small carnivorous dinosaurs, rather than the explosively fast growth seen in modern birds.[4]
In absolute number of features shared with modern birds,S. chaoyangensis is about as derived asConfuciusornis. However, theapomorphies were largely different fromConfuciusornis, and a character analysis demonstrates that these two were not closely related.[5] The tail plumage ofSapeornis consisted of rectrices that formed a graded, fan-like structure. The reduced fingers suggest that it might have had analula. Not being well-adapted to flapping flight,Sapeornis probably was a glider and/or soarer that preferred more open country compared to the Enantiornithes and predominantly woodland birds, although it was able to perch on branches. The small gastroliths, overall large size, and the inferred habitat indicate thatSapeornis was most likely aherbivore, possibly eating plant seeds and fruits.[6]
Comparisons between thescleral rings ofSapeornis and modern birds and reptiles indicate that it may have beendiurnal, similar to most modern birds.[7]
Sapeornis is known from fossils found inJiufotang Formation andYixian Formation rocks in western Liaoning, China. These rocks formed during thelate Aptian through earlyAlbian epochs of the Cretaceous period, and are about 125-120 million years old. Several nearly complete skeletons have been found.[6]
The first known specimen (thetype specimen) ofSapeornis was an incomplete skeleton dug up from Jiufotang Formation rocks in the area of Shangheshou, nearChaoyang City in Liaoning Province, China in the summer of 2000. It was discovered by a team from theInstitute of Vertebrate Paleontology and Paleoanthropology (IVPP), and was reported in 2002 by the scientists Zhonghe Zhou and Fucheng Zhang.[8] They chose the name in honor of SAPE, theSociety of Avian Paleontology and Evolution, which they combined with theAncient Greek wordόρνις (ornis), meaning "bird". The species namechaoyangensis isLatin for "from Chaoyang".[9] Soon after this, two more, nearly complete specimens were discovered in the Dapingfang area, about 40 kilometres (25 mi) from the original fossil site. None of these first three specimens preserved traces of feathers, but based on the size of their skeletons alone, they were recognized as the largest early Cretaceous avialans known at the time.[9]
In 2008, Yuan named a new specimen related toSapeornis asDidactylornis jii. Yuan concluded thatDidactylornis differed fromSapeornis in the proportions of the foot and number of wing and foot bones.[10] However, the relevant portions of the specimen were badly crushed, and later authors concluded that these differences were based on misinterpretation of the poorly preserved specimen. In a 2010 survey of Chinese avialan fossils, Li and colleagues consideredDidactylornis a synonym ofSapeornis chaoyangensis.[11] In a 2012 study, Gaoet al. concluded thatDidactylornis was indeed a junior synonym ofSapeornis chaoyangensis, as wereShenshiornis and the supposed second species ofSapeornis,S. angustis.[12]Omnivoropteryx is also likely synonymous withSapeornis.[13]
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