Xiaotingia Zhengi

''Xiaotingia'' is a genus of anchiornithid theropod dinosaur from Middle Jurassic or early Late Jurassic deposits of western Liaoning, China, containing a single species, ''Xiaotingia zhengi''.

Discovery

''Xiaotingia'' is known from the holotype STM 27-2, an articulated and almost complete skeleton including the skull. It was probably collected in the Linglongta area, Jianchang, from the Tiaojishan Formation.

Etymology

''Xiaotingia'' was first named by Xu Xing, You Hailu, Du Kai and Han Fenglu in 2011 and the type species is ''Xiaotingia zhengi''. The generic name and specific name together honour paleontologist Zheng Xiaoting.

Description

''Xiaotingia'' lived around 155 million years ago which preceded ''Archaeopteryx'' that lived around 144 million years ago.

''Xiaotingia'' was morphologically similar to ''Archaeopteryx'' and was the size of a hen. It was about 60 cm long and weighed an estimated 0.82 kg. It was a small feathered dinosaur that lived in an arboreal environment. Like ''Archaeopteryx'' it had long forelimbs. Its femur was longer than its humerus, 84 mm compared to 71 mm, which might indicate that it stood on its hind limbs and could flap its forelimbs to achieve flight.

''Xiaotingia'' had feathers on its head, body, forelimbs and hind limbs. The feathers on the femur were quite long, measuring 55 mm. It also had long pennaceous feathers on its tibia and metatarsus. If ''Xiaotingia'' could fly short distances it might also have used its hind limbs as wings.

''Xiaotingia'' had a dentary tooth count probably less than 10 and teeth similar in morphology to those of basal avians.

Classification

The initial analysis by Xu ''et al.'' showed that ''Xiaotingia'' formed a clade with ''Archaeopteryx'', Dromaeosauridae and Troodontidae to the exclusion of other groups traditionally seen as birds. Xu ''et al.'' therefore (re)defined the concepts of Deinonychosauria and Avialae to the extent that ''Archaeopteryx'' and ''Xiaotingia'' belonged to the Deinonychosauria in the clade Archaeopterygidae. This led to popular reports that "''Archaeopteryx'' is no longer a bird", although Xu ''et al.'' noted that there are several competing definitions of the clade Aves currently in use, pointing out that their definitions are compatible with a traditional Aves with ''Archaeopteryx'' as a specifier. This was challenged by an analysis using different methods published several months later however, in which ''Archaeopteryx'' was again recovered as an avialan, while ''Xiaotingia'' remained closely allied to ''Anchiornis'' within the Troodontidae. In 2012, an expanded and revised version of the initial analysis also found ''Archaeopteryx'' to be avialan and ''Anchiornis'' to be troodontid, but recovered ''Xiaotingia'' as the most primitive member of the clade Dromaeosauridae rather than a close relative of ''Anchiornis'' within Troodontidae.


Cladogram following the results of a phylogenetic study by Lefèvre ''et al.'', 2017.Ulysse Lefèvre, Andrea Cau, Aude Cincotta, Dongyu Hu, Anusuya Chinsamy, François Escuillié & Pascal Godefroit (2017). A new Jurassic theropod from China documents a transitional step in the macrostructure of feathers. ''The Science of Nature'', 104: 74 (advance online publication).

In 2017 re-evaluation of the Harlem ''Archaeopteryx'' specimen, ''Xiaotingia'' is found to be an anchiornithid.

See also

* Timeline of troodontid research

References

{{Taxonbar, from=Q568269

Late Jurassic dinosaurs of Asia
Troodontids
Jurassic birds
Feathered dinosaurs
Transitional fossils
Fossil taxa described in 2011
Taxa named by Xu Xing
Paleontology in Liaoning