Shishugou Formation dinosaur traps

The Shishugou Formation dinosaur traps also known as death pits or death traps are found in the Shishugou Formation, located in the Junggar Basin within Xinjiang Province of northwestern China. They are a rich source of Jurassic Period dinosaur fossils, many of which were new species to palaeontology.

The Junggar Basin is a large continental basin made up of fluviatile and lacustrine sediments up to 6 kilometres (3.7 mi) thick. The sites are some 95 km NNE of the town Qitai.

These 'traps' or 'bonebeds' are unusual in that they consist of vertically stacked skeletons of numerous non-avian theropods in 1–2 metres (3.3–6.6 ft) deep pits. The pits are filled with a mix of alluvial and volcanic mudstone and sandstone and appear to have been created by the trampling and wallowing of large dinosaurs. 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. The high quality of preservation suggests a rapid burying of the carcasses. Some scavenging of the bodies took place leading to a dispersal of body parts. Smaller vertebrates were prone to getting stuck in these mudholes, and the small ceratosaur, Limusaurus inextricabilis, is the most common in the resulting bonebeds.

Excavations since 2000 have revealed a wealth of fossils dating from a period some 165 to 155 million years ago. 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. These new branches on the dinosaur family tree led to well-known dinosaur groups, such as the horned ceratopsians, armoured stegosaurs, and tyrannosaurs. 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.

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