Scientists have uncovered a wealth of well-preserved fossils in China from the early Cambrian Period, representing 101 species so far, over half of which have never been described before.
In 1909, scientists discovered a trove of fossils in British Columbia, known today as the Burgess Shale fossils. These fossils differed from others in that they preserved the structures of soft matter, revealing things such as eyes and guts or the bodies of soft animals like jellyfish.
Burgess Shale-type fossils have since been discovered around the world, helping scientists piece together the story of the Cambrian Period 500 million years ago and the burst of new species around that time — a stage known as the Cambrian explosion.
The newest discovery from the Danshui River, called the Qingjiang biota, rivals existing fossil assemblages in how well it preserves the included species, the diversity of species included, and the proportion of new species.
“The particularly large proportion of new taxa in the Qingjiang biota… suggests that the present understanding of the diversity and disparity of metazoan ecosystems in the immediate aftermath of the Cambrian explosion is far from complete and will be greatly informed by future discoveries,” the authors from Northwest University and Guizhou University in China and Pomona College in California write in the paper published this week in Science.
The assemblage of fossils represents 4351 specimens in a region calculated to be 518 million years old, according to the paper. Of the 101 new species identified, 53 per cent were new, and 85 per cent had soft bodies.
The most diverse groups included arthropods (an invertebrate group that includes spiders and crustaceans) and sponges. The fossils represent groups from the sea bottom, in the sea sediment itself, and ones that float and swim around like jellyfish.
Surprisingly, only eight species were shared with the Chengjiang biota, another similarly aged Burgess Shale-type fossil site 1050km away. These differences are surprising but likely represent a difference in the ecology between the two places 518 million years ago.
“The comparison of the two biotas offers a rare opportunity to understand how early metazoan communities developed in response to environmental parameters,” the authors write.
It’s an exciting find for other reasons, too.
“The cnidarians, which include corals, sea anemones and jellyfish, are relatively rare and not particularly diverse in previously known Cambrian Explosion localities. In contrast, the Qingjiang biota reveals a high abundance and diversity of cnidarians, which make up more than one-third of the specimens reported,” Allison Daley, an associate professor of the geosciences at the University of Lausanne in Switzerland who was not involved in the study, wrote in a perspective for Science.
“Free-swimming jellyfish and sea anemones attached to the seafloor are both present, with detailed anatomies that make them instantly recognisable.”
New fossil troves such as these are exciting for the way they can serve as another missing piece to the puzzle of the Cambrian Period. The authors write that there is “great potential for continued discovery of new taxa with further excavation at Qingjiang and elsewhere in the region”.
The site represents an important snapshot from the Cambrian explosion — a time beginning around 542 million years ago when a diverse array of animals suddenly appear in the fossil record. This period likely marked the beginning of many of the marine-based animal interactions that still exist today.