A Study Of The New Dromaeosaurid Dinosaur From The Early Cretaceous Of Jiuquan Area, Gansu Province, China

Background:The Yujingzi Basin in Gansu Province is one of the famous diversity of Lower Cretaceous dinosaur fauna in China. In 2007, Excavation of the Fossil Research and Development Center (FRDC) found out a new dromaeosaurid specimen from the Lower Cretaceous Zhonggou Formation (Early Cretaceous, Aptian?-Albian). The specimen was collected at the locality called "Baichengzi" about 21.8 km northeast of Jiayuguan city.The fossil assemblages of the Gansu Province is dominated by large-bodied dinosaur species, such as the Suzhousaurus megatherinoides (Therizinosauridae) and Equijubus normani (Hadrosauridae), or basal Neoceratopsian dinosaur such as Archaeoceratops yujingziensis and Auroraceratops rugosus. Thus, the small bodied dinosaur is pretty rare, and small carnivorous theropods have not been reported from these beds except for Xiongguanlong baimoensis in this area. It is probable that FRDC-GJ(07)11-2 is an important evidence for reconstruction of the ecosystem at the Lower Cretaceous Jiuquan area. Additionally, the specimen consists of the left frontal,3 dorsal vertebrae, sacrum,3 caudal vertebrae, left scapula, left humerus,3 manual phalanges, right ilium, right ischium, right pubis, and 4 pedal phalanges.Methodology/Principal Findings:A middle sized dromaeosaurid diagnosed by the following combination of characters and autapomorphies; the frontal is approximately twice as long anteroposteriorly as wide transversely behind the orbit. The supratemporal fossa is well-separated from the midline. The ventral hypapophysis is absent in dorsals, and the neurocentral suture is closed in all of the centra. The hyposphene-hypantrum articulation is clearly delineated, thoracic vertebral centra with lengths markedly greater than midpoint widths. Sacrum is consisted of six sacral elements, and the zygapophyses of sacral vertebrae are fused and formed a sinuous ridge in dorsal view. The shallow sulcus is absent on the ventral midline of the three middle sacra. The scapula and the coracoid are separated, and the acromion process of the scapula does not project anteriorly past the articular surface for the coracoid. The heel of the proximal articular surface of manual phalanx III-3 is relatively low in lateral view. The flexor heel on pharanx Ⅱ-2 that is long and lobate, with an extension of the midline ridge onto the dorsal surface of the heel. The articular surface of the pedal phalanx Ⅱ-2 is bilaterally symmetrical in proximal view, and it lacks a proximoventral expansion of the flexor heel. I performed a phylogenetic analysis at species-level within the larger context of Deinonychosauria based on a published study (Turner, et al.2012) in order to determine the phylogenetic position of the FRDC-GJ(07) 11-2 with TNT 1.0 (http://www.zmuc.dk/public/phylogeny/tnt/) and Mesquite (https://mesquiteproject. wikispaces.com/home).Conclusions/Significance:The phylogenetic place of this FRDC-GJ(07)11-2 is in the dromaeosaurid clade Eudromaeosauria (Velociraptorinae+Dromaeosaurine). Its clade and FRDC-GJ(07)11-2 are shared following apomorphic character; The flexor heel on pharanx Ⅱ-2 that is long and lobate, with an extension of the midline ridge onto the dorsal surface of the heel (character.228-1), thoracic vertebral centra with lengths markedly greater than midpoint widths(character.317-0), and the acromion process of the scapula does not project anteriorly past the articular surface for the coracoid(character.354-1). Most important autapomorphy of this dromaeosaurid dinosaur is the lacks a proximoventral expansion of the flexor heel of pedal phalanx Ⅱ-2 in proximal view (Fig.). This feature probably didn’t exist in other Deinonychosauria.The first discovery of dromaeosaurid dinosaur in Gansu Province, suggests there may be a rich dinosaur fauna at Lower Cretaceous in surround area, and it should inspire greater efforts to further research of eudromaeosauria in Northwest China, because the eudromaeosaurian dinosaur is still very few throughout China. Unfortunately this specimen is lacking the most part of the skull, very little is currently known about the structure of the skull that is necessary for analysis, so it is to be hoped that future discovery will clarify this point.