Paleontologia 2015

Paleontologia 2015

The First Dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous Bayan Gobi Formation of Nei Mongol, China

Figure 6. A palaeoreconstruction of IVPP V22530 next to its inferred depositional setting, a muddy lake environment.

Illustration: Julius T. Csotonyi || DOI: 10.7287/PeerJ.preprints.1340v1

Abstract

The first dromaeosaurid theropod from the Early Cretaceous Bayan Gobi Formation is identified based on an incompletely preserved partially-articulated left leg, increasing the known diversity of its understudied ecosystem. The leg belongs to specimen IVPP V22530 and includes a typical deinonychosaurian pedal phalanx II-2 with a distinct constriction between the enlarged proximal end and the distal condyle as well as a typical deinonychosaurian enlarged pedal phalanx II-3. It possesses a symmetric metatarsus and a slender and long MT V that together suggest it is a dromaeosaurid. Two anatomical traits suggest the leg is microraptorine-like, but a more precise taxonomic referral was not possible: metatarsals II, III and IV are closely appressed distally and the ventral margin of the medial ligament pit of phalanx II-2 is close to the centre of the rounded distal condyle. This taxonomic status invites future efforts to discover additional specimens at the study locality because - whether it is a microraptorine or a close relative - this animal is expected to make important contributions to our understanding of dromaeosaurid evolution and biology. IVPP V22530 also comprises of an isolated manual ungual, a proximal portion of a right dorsal rib and an indeterminate bone mass that includes a collection of ribs. However, these specimens cannot be confidently referred to Dromaeosauridae, although they may very well belong to the same individual from whom the left leg belongs.

Keywords: dromaeosaurid, microraptorine, paravian, deinonychosaur, theropod, Elesitai, Bayan Gobi Formation, Nei Mongol, Early Cretaceous

Conclusions

IVPP V22530 comprises of an incompletely preserved partially-articulated left dromaeosaurid leg, an isolated pennaraptorans manual ungual, a proximal portion of a right theropod dorsal rib and an indeterminate bone mass that includes a collection of ribs. Two anatomical traits suggest that the left leg belongs to a microraptorine or a close relative: metatarsals II, III and IV are closely appressed distally and the ventral margin of the medial ligament pit of phalanx II-2 is close to the centre of the rounded distal condyle. This referral means that IVPP V22530 is the first described dromaeosaurid - and small-sized theropod (<1kg -="" a="" age="" ages="" albian="" american="" and="" aptian="" are="" area="" as="" at="" bayan="" be="" because="" been="" between="" biology="" but="" campanian="" clade="" close="" constraining="" could="" cretaceous.="" cretaceous="" discoveries="" div="" dromaeosaurid.="" dromaeosaurid="" early="" ecosystem.="" evolution="" example.="" expand="" extend="" fill="" first-known="" first="" for="" formation="" from.="" from="" further="" gaps="" geographical="" gobi="" have="" help="" helping="" important="" in="" invaluable="" is="" ivpp="" km="" knowledge="" known="" lbian="" liaoning="" make="" microraptorine-like="" microraptorine="" microraptorines="" non-north="" northwest="" of="" only="" our="" province="" range="" relative="" site="" specifically="" stages="" study="" suggested="" supported="" that="" the="" them="" this="" thus="" to="" understanding="" understudied="" v22530="" well="" which="" will="" would="">

Michael Pittman​, Rui Pei and Xing Xu. 2015. The First Dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous Bayan Gobi Formation of Nei Mongol, China. PeerJ. PrePrints 3:e1654 DOI: 10.7287/PeerJ.preprints.1340v1