[D] Xiaotingia zhengi [sG] [T]
Describer
Xu, You, Du & Han 2011
Time
Jurassic Late
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Archaeopterygidae
Diet
Carnivore
Fossilsite
Tiaojishan Formation,Linglongta, Jianchang, western Liaoning, China
Info
Archaeopteryx is widely accepted as being the most basal bird, and accordingly it is regarded as central to understanding avialan origins; however, recent discoveries of derived maniraptorans have weakened the avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like theropod from China. This find further demonstrates that many features formerly regarded as being diagnostic of Avialae, including long and robust forelimbs, actually characterize the more inclusive group Paraves (composed of the avialans and the deinonychosaurs).
Notably, adding the new taxon into a comprehensive phylogenetic analysis shifts Archaeopteryx to the Deinonychosauria. Despite only tentative statistical support, this result challenges the centrality of Archaeopteryx in the transition to birds. If this new phylogenetic hypothesis can be confirmed by further investigation, current assumptions regarding the avialan ancestral condition will need to be re-evaluated.
An initial cladistic analysis by Xu et al. showed that Xiaotingia formed a clade with Archaeopteryx , the Dromaeosauridae and the Troodontidae to the exclusion of other forms 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 and Archaeopteryx no longer was an avialan.
This led to popular reports that \\\"Archaeopteryx is no longer a bird\\\", though 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. However, this was challenged by a more thorough analysis published several months later, in which Archaeopteryx was again recovered as an avialan, while Xiaotingia remained closely allied to Anchiornis within the Troodontidae.
Etymology
Generic name and specific name together in honour of Zheng Xiaoting for his efforts in establishing the Shandong Tianyu Museum of Nature as a repository for vertebrate fossils from China.
Holotype
STM (Shandong Tianyu Museum of Nature) 27-2, an articulated skeleton, missing parts of the pelvis and hindlimbs and most of the caudal vertebrae, with some associated integumentary structures.
Diagnosis
A small paravian with the following unique features: the maxillary posterior ramus has a depth at mid-length exceeding that of the dentary; the surangular has little lateral exposure and forms a wide, flat dorsal surface over the posterior part of the mandible; an extremely large surangular foramen extends over more than 6% of the total mandibular length; the posterior end of the mandible is blunt and dorsoventrally expanded; the anteriormost caudal centra are less than half as long as the posterior dorsal centra; metacarpal IV is more robust than metacarpals II and III; and manual phalanx III-2 is longer than metacarpal III (we identify the three manual digits of Xiaotingia and other maniraptorans as II-III-IV, rather than as I-II-III as in many other studies).
Xu, You, Du & Han 2011
Time
Jurassic Late
Classification
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Archaeopterygidae
Diet
Carnivore
Fossilsite
Tiaojishan Formation,Linglongta, Jianchang, western Liaoning, China
Info
Archaeopteryx is widely accepted as being the most basal bird, and accordingly it is regarded as central to understanding avialan origins; however, recent discoveries of derived maniraptorans have weakened the avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like theropod from China. This find further demonstrates that many features formerly regarded as being diagnostic of Avialae, including long and robust forelimbs, actually characterize the more inclusive group Paraves (composed of the avialans and the deinonychosaurs).
Notably, adding the new taxon into a comprehensive phylogenetic analysis shifts Archaeopteryx to the Deinonychosauria. Despite only tentative statistical support, this result challenges the centrality of Archaeopteryx in the transition to birds. If this new phylogenetic hypothesis can be confirmed by further investigation, current assumptions regarding the avialan ancestral condition will need to be re-evaluated.
An initial cladistic analysis by Xu et al. showed that Xiaotingia formed a clade with Archaeopteryx , the Dromaeosauridae and the Troodontidae to the exclusion of other forms 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 and Archaeopteryx no longer was an avialan.
This led to popular reports that \\\"Archaeopteryx is no longer a bird\\\", though 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. However, this was challenged by a more thorough analysis published several months later, in which Archaeopteryx was again recovered as an avialan, while Xiaotingia remained closely allied to Anchiornis within the Troodontidae.
Etymology
Generic name and specific name together in honour of Zheng Xiaoting for his efforts in establishing the Shandong Tianyu Museum of Nature as a repository for vertebrate fossils from China.
Holotype
STM (Shandong Tianyu Museum of Nature) 27-2, an articulated skeleton, missing parts of the pelvis and hindlimbs and most of the caudal vertebrae, with some associated integumentary structures.
Diagnosis
A small paravian with the following unique features: the maxillary posterior ramus has a depth at mid-length exceeding that of the dentary; the surangular has little lateral exposure and forms a wide, flat dorsal surface over the posterior part of the mandible; an extremely large surangular foramen extends over more than 6% of the total mandibular length; the posterior end of the mandible is blunt and dorsoventrally expanded; the anteriormost caudal centra are less than half as long as the posterior dorsal centra; metacarpal IV is more robust than metacarpals II and III; and manual phalanx III-2 is longer than metacarpal III (we identify the three manual digits of Xiaotingia and other maniraptorans as II-III-IV, rather than as I-II-III as in many other studies).