| Yandangornis | |
|---|---|
 | |
| Holotype specimen | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Clade: | †Yandangithiformes Cai & Zhao, 1999 |
| Family: | †Yandangithidae Cai & Zhao, 1999 |
| Genus: | †Yandangornis Cai & Zhao, 1999 |
| Species: | †Y. longicaudus |
| Binomial name | |
| †Yandangornis longicaudus Cai & Zhao, 1999 | |
Yandangornis is agenus oftheropods (possiblyavialans) from theLate CretaceousTangshang Formation ofChina. It lived 81.5million years ago in what is now China. Thetype species,Y. longicaudus, was formally described by Cai and Zhou in 1999.
Theholotype specimen is a mostly complete skeleton in the collection of theZhejiang Museum of Natural History, with accession number M1326. The fossil was discovered in 1986, near Linhai City in Zhejiang Province, China. It includes most of one complete skeleton. The genus was named after theYandang mountains.
The specimen is small, roughly the size ofArchaeopteryx, with a total length around 58.8 centimetres (1.93 ft), of which 30.5 centimeters (1 foot) is tail. It is preserved in a seated position and visible from theventral aspect. AfterArchaeopteryx,Yandangornis was the second genus of primitive bird found preserving a long, bony tail, and this trait was responsible for thespecific namelongicaudus, which isLatin for "long tail".
The skull is flattened, about 50 millimetres (2.0 in) long. It is lightly built and toothless, with a short mouth and robustpremaxillae presumably possessing a hornybeak. These characteristics are similar to those ofConfuciusornis. The forelimbs, though incomplete, are generally similar to those ofArchaeopteryx. Thesternum is large and unkeeled, but possesses an expanded middle posterior portion andgastralia. The hind limbs are long and robust, particularly thefemur andtibiotarsus. Thefibula andtarsometatarsus, on the other hand, are short. The small first toe is at a higher level than the other three toes and does not possess a reversed hallux. The toes were long and slender, with short, blunt claws. Unlike in several other avialans andparavians, the second toe did not have a large, curved claw.[1]
Yandangornis had some features that suggest a terrestrial mode of life, such as blunt toe claws, a non-reversed hallux of the first toe, and strong legs. This lifestyle may have evolved in response to the long, heavy tail of the genus, which would have inhibited flying ability.[1]
Cai and Zhao placedYandangornis in amonotypicfamily (Yandangithidae) andorder (Yandangithiformes) in the subclassSauriurae of theclassAves. In fact, they considered that it was a direct descendant ofArchaeopteryx, albeit as part of a lineage of long-tailed terrestrial birds distinct from modern birds.[1] However, Sauriurae (long-tailed birds) has generally been discredited as an invalidparaphyletic group.[2] Aves, on the other hand, is currently restricted to the last common ancestor of all living birds and its descendants. AsYandangornis was far more primitive than members of Aves, it is not considered a member of that class using recent definitions. The usage of Aves within the description ofYandangornis more closely resembles the current cladeAvialae, which is defined as all animals more closely related to modern birds (Aves) than toTroodontids andDromaeosaurids.[3] Other long-tailed avialans includeJeholornis andArchaeopteryx.
Zhou and Zhang, 2007, briefly noted thatYandangornis's affinities were not sufficiently diagnosed, and thatYandangornis may potentially be a non-avialan genus of theropod.[4]Yandangornis is poorly documented in literature, and discussion of the genus has generally been omitted from recent reevaluations of avialansystematics.
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