Largest dinosaur tracksite in China (Cretaceous, Zhaojue area, Sichuan Province): On the verge of destruction

The Zhaojue (ZJ) tracksites represent multiple steeply-inclined, track-bearing exposures in the clastic Feitianshan Formation of Sichuan Province that have been sequentially, excavated, mapped, expanded and destroyed, by quarrying, erosion or collapse, for almost three decades. The quarried area extends for more almost 1.0 km from north to south and ~ 0.5 km from east to west. Four important track-bearing surfaces have been identified and identified as ZJ-I, ZJ-II, ZJ-IIN and ZJ-III, some of which are newly exposed surfaces or expanded surfaces that were previously partially described. Others represent surfaces lost since they were first reported in papers published in 2014–2016. The ZJ-II site represents a hugely expanded continuation of a much smaller track-bearing surface described in 2014. It was mapped using drone technology, and now represents the largest tracksite in China, with a minimum count of 933 recognizable tracks, and the longest recorded sauropod and ornithopod trackways from China (~80 m and ~52 m respectively), which also reveal a pronounced change in the direction of trackmaker movement. The ZJ-II surface represents the best Zhaojue paleo-census sample giving a count of 68 individuals from 61 trackways (37 ornithopod, 10 theropod, 14 sauropod) and isolated tracks (representing 7 individuals). Thus, ornithopods (both large and small trackmakers) represent ~54% of the total number of trackways. The smaller ZJ-III surface was mapped using traditional methods, and reveals at least 6 ornithopod- and 4 theropod trackways. Both the ZJ-II and ZJ-III surfaces reveal parallel ornithopod trackways suggestive of social or gregarious behavior. The combined data from all four Zhaojue surfaces reveal a total of 1928 tracks, and include a few previously reported pterosaurs and theropod swim tracks. The Zhaojue quarry complex provide a good example of multiple track-bearing sites (surfaces) that require long term study and monitoring to extract as much trackway data as possible before in situ physical evidence is lost.