The first theropod tracks from the Middle Jurassic of Gansu, Northwest China: new and rare evidence of quadrupedal progression in theropod dinosaurs

Da-Qing Li,Li-Da Xing,Martin G Lockley,Anthony Romilio,Long-Feng Li,Jing-Tao Yang

doi:10.1186/s42501-019-0028-4

Abstract

A new Middle Jurassic tracksite dominated by non-avian theropod footprints from the Wangjiashan Formation in Pingchuan District, Baojishan Basin, Gansu Province has yielded a unique trackway with four consecutive manus-pes sets. Only three previous examples, all Early Jurassic in age, of theropod trackways are known with convincing examples of manus tracks and in each case, only two tracks were recorded in association with pes tracks with metatarsal impressions and pelvic traces indicating crouching behavior. Thus, this is the first example of manus tracks registered while a theropod trackmaker was walking. This unique configuration is here designated as Grallator pingchuanensis ichnosp. nov. which shows the trackmaker forelimbs registering in a wide straddle gait, much wider than the pes trackway width. G. pingchuanensis confirms previous reports that theropods could occasionally register tridactyl, ectaxonic manus traces. In the case of the Pingchuan trackway, the short step indicates an animal moving at a slow speed, probably due to a soft substrate.

Highlights

The discovery of dinosaur fossils in Gansu Province can be traced to 1930–1931 when the Sino-Swedish Expedition collected the first dinosaur material from the Mesozoic basins of western Gansu (Bohlin 1953)
In 2018, authors of this study investigated this tracksite again to make resin and 3D digit models
We inferred that no example of theropod manus tracks was found in association with a normal, walking trackway rather than a crouching posture. For this reason we proposed that the crouching trace represents a mode of theropod locomotion not reported previously and that the morphological configuration of the trackway has not previously been described

Summary

Introduction

The discovery of dinosaur fossils in Gansu Province can be traced to 1930–1931 when the Sino-Swedish Expedition collected the first dinosaur material from the Mesozoic basins of western Gansu (Bohlin 1953). One possible Late Jurassic sauropod was found in the central part of Gansu before this study (Young 1948). This was eventually attributed to the sauropod genus Mamenchisaurus (Young and Zhao 1972). All other records from this region, including abundant skeletons and tracks, are from the Lower Cretaceous rock units. In Gansu, the Yanguoxia tracksites yielded the most abundant and diverse track records, including well-preserved sauropod, ornithopod, dromaeosaur, theropod, pterosaur, and bird tracks and trackways (Zhang et al 2006; Xing et al.2013a, 2016a, 2016b; Li et al 2015). In the Honggu (Xing et al 2014a), Zhongpu (Xing et al 2014b, 2015), Guanshan (Xing et al 2016a), and Changma (Xing et al 2017) areas, some non-avian dinosaur and bird tracks were discovered

Methods

Discussion

Conclusion