If you visited the oceans more than 500 million years ago, you would find yourself in an alien world. Creatures with quilted folds of soft tissue sat on the sea floor like carpets and life forms that looked like fringed plants but were actually animals anchored to the ocean floor. But one organism may be somewhat familiar: a stalking, cup-like creature with fluttering tentacles resembling those of a jellyfish. The newly described fossil of this organism, named Auroralumina attenboroughii after naturalist and broadcaster David Attenborough, is between 556 million and 562 million years old and may be the oldest example of an evolutionary group still living today.
When co-author and University of Oxford paleobiologist Frances Dunn saw a cast of the fossil, she says, “It was immediately clear that this was really special and really rare.” With other fossils from the Ediacaran period, between 635 million and 541 million years old, her first impression it is often “What is this? How can I connect this to something that’s alive today?’ But with this specimen, she thought, ‘I know what this is.’
Classical scientific wisdom places the origin of modern animals around 539 million years ago during what is called the Cambrian explosion. Around this time, creatures with specialized tissues, organs, intestines, and symmetrical left and right sides began to appear—all traits we recognize in today’s animals.
In recent years, fossil finds from the earlier Ediacaran period have begun to challenge this dogma. This is especially true for creatures that can be classified as cnidarians, a group of marine animals that includes today’s jellyfish, corals, and sea anemones. A cup-shaped creature with a tangle of tentacles called Haootia quadriformis dates from about the same age as A. attenboroughiibut its relatively poor preservation makes its exact relationship to extant animals difficult to analyze.
Palaeobiologist Philip Wilby and colleagues from the British Geological Survey discovered the new fossil in Charnwood Forest, a hotbed of Precambrian palaeontology in a hilly area of Leicestershire in central England. They dated the rocks surrounding the fossils to between 556 million and 562 million years old, using the radioactive decay of uranium into lead.
The 8-inch (20-centimeter) fossil — about the length of a dinner fork — is the imprint of a two-toothed creature with long stalks covered in tentacled cups. The organism appears to be in the polyp stage, the life cycle when the cnidarian clings to the ocean floor and uses its tentacles to grab tasty larvae and floating plankton. The body of A. attenboroughi it has fourfold symmetry, meaning it is symmetrical around the four corners of a central point, as are modern jellyfish.
The researchers made a cast and a detailed drawing of the fossil, which they examined and manipulated on a computer to better see the creature in different lighting. They then used another computer program to record the physical features of the fossil and place it on an evolutionary tree.
The team concluded that A. attenboroughi is a cnidaria and a member of the subgroup called medusozoans, which includes modern jellyfish, reported today in Natural ecology and evolution. If true, “our fossil becomes the oldest animal with direct living descendants in the fossil record — period,” Dunn says.
“It’s closer to a modern animal group than anything else of this age or older,” agreed Alexander Liu, a paleobiologist at the University of Cambridge who was not involved in the new find; he was part of the team he described Eat it in 2014. Still, he wishes the authors had more carefully compared the new fossil to groups such as the coral-containing cnidarian subgroup anthozoans.
As for the alliterative name of the creature, the researchers chose Aurora Lumina because of its status as an early animal and because the shape reminds Dunn of the Olympic torch; in latin, Aurora means dawn and lumina means light. And they chose attenboroughii for Attenborough had spent his boyhood near Charnwood, and paid attention to its fossils. “He grew up trampling these ancient forests, so we wanted to name the species after him,” says Dunn.