Early Record of the Cambrian Explosion
James W. Hagadorn
When I found the first fossil … I knew right away that it was an arthropod with paired appendages, extending forward, as if it was swimming on the moistened surface of a mudstone. But I realized that you could see the impression of the soft body parts. That night I put the fossils under my bed. But because I was so excited, I couldn't sleep very well. I got up often and pulled out the fossils just to look at them.
This is how Chinese paleontologist Hou Xianguang (personal communication, 2000) describes his initial reaction to the discovery of the Chengjiang Lagerstätte. In 1984, Hou was working on bradoriid-rich deposits at Maotian Hill, near the town of Chengjiang in the Yunnan Province of China (Figure 3.1). He split open a rock on the west face of the mountain to reveal an unusual arthropod: the softbodied trilobite Naraoia (Gore 1993; Monastersky 1993). Although a few obscure soft-bodied fossils from the Chengjiang deposit had been published (Mansuy 1912; Pan 1957), Hou was the first to recognize both Chengjiang's status as a Lagerstätte and its link to other soft-bodied deposits like the Burgess Shale. Considering the impact this deposit has had on the paleontological community, his enthusiastic reaction was more than justified.
The Chengjiang deposit is a conservation Lagerstätte that contains a variety of soft-bodied and biomineralized metazoans representing one of the earliest records of the Cambrian explosion in metazoan diversity. The Chengjiang biota is quite diverse, including algae, acritarchs, sponges, chancellorids, anemones, ctenophores, hyoliths, inarticulate