Small theropods and vertebrates then became mired in these pits, dying and being forced deeper by the activities of the large dinosaurs and the struggles of later victims.

Smaller vertebrates were prone to getting stuck in these mudholes, and the small ceratosaur, Limusaurus inextricabilis, is the most common in the resulting bonebeds.

Palaeontologists James Clark and Xu Xing are shedding light on this period previously notorious for its paucity of fossils, but important for its massive burst of speciation among the dinosaurs and ancestors of birds.

Clark joined Xu, from Beijing's Institute of Vertebrate Paleontology and Paleoanthropology, to explore the Junggar Basin, and in particular the Shishugou Formation, where the exposed rocks have been linked to the Middle Jurassic.

Currently it is a sparsely settled region of dry washes, arid badlands and dunes along the Gobi Desert’s western edge.

The Shishugou Formation consists of mudstone, siltstone, and sandstone, and is named for the silicified wood or petrified logs found here.

Yang Zhongjian accompanied the first expedition to the Junggar Basin in 1928, and the fossils found included the medium-size sauropod Tienshanosaurus chitaiensis.

The most interesting of the traps gave up the fossil remains of an 80 kg tyrannosauroid named Guanlong, sporting a crest running from its nose to the back of its head.