Scientists have unearthed in southern China fossils of a multitude of marine creatures dating to more than a half billion years ago, showing a deep-water ecosystem thriving in the aftermath of the first mass extinction of the animal world.
The Cambrian Period fossils, about 512 million years old, are of invertebrates of various shapes and sizes, including an apex predator with menacing grasping appendages. They are exceptionally well-preserved sometimes down to the cellular level, revealing legs, gills, guts, eyes and even nerves.
The researchers collected more than 50,000 fossil specimens in mudstone from a single quarry, representing a highly diverse assemblage of organisms they call the Huayuan biota, named after the county in Hunan province where it is located. They examined a sample of 8,681 specimens and recognised 153 species – 91 of which were previously unknown – from 16 major animal groups.
The fossils date to a time when animal and plant life was still confined to the seas. They rival two other important fossil assemblages in providing a look at life in the Cambrian seas – the Burgess Shale biota of Canada’s province of British Columbia and the Chengjiang biota of China’s Yunnan province.
“The Huayuan biota was situated at a deep-water environment at the edge of the continental shelf of South China,” said Han Zeng, a palaeontologist at the Nanjing Institute of Geology and Palaeontology.
“The Huayuan biota was a thriving ecosystem with animals distributed from the water column to the surface and inside of marine sediment. The animals have various feeding habits and motility,” Zeng said.
The dominant groups among the fossils included: arthropods, the group that includes today’s crabs, shrimp, scorpions, insects, spiders, centipedes and millipedes; cnidarians, which include today’s jellyfish, corals and sea anemones; and sponges, which are among the oldest animals.
The top predators were several members of a group of primitive arthropods called radiodonts that had raptorial appendages – specialised limbs to grab prey while swimming through the sea. Another creature was covered with spines and looked vaguely like a cactus.
While the animals discovered were all invertebrates, the Huayuan biota does include diverse and abundant members of a subdivision of animals considered the closest relatives of vertebrates.
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