If you visited the oceans more than 500 million years ago, you’d find yourself in an alien world. Beings with quilted folds of soft tissue sat on the seabed like rugs, and life forms that looked like fronded plants but were actually animals made anchor on the ocean floor. But one organism might be somewhat familiar: a stalked, cuplike creature with waving 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 instantly clear that this was really special and really rare.” With other fossils from the Ediacaran period, between 635 million and 541 million years ago, her first impression often is “What is this? How can I relate this to anything that’s alive today?” But with this specimen, she thought, “I know what this is.”
Classical scientific wisdom places the origin of modern animals about 539 million years ago during what’s called the Cambrian explosion. At this time, creatures with specialized tissues, organs, guts, and symmetrical left and right sides—all traits we recognize in the animals of today—began popping up.
In more recent years, fossil finds from the earlier Ediacaran period have begun to challenge this dogma. That’s especially true of creatures that could be classified as cnidarians, a group of marine animals that includes today’s jellyfish, corals, and sea anemones. One goblet-shaped creature with a tangle of tentacles called Haootia quadriformis dates to about the same age as A. attenboroughii, but its relatively poor preservation makes its exact relationship to existing animals hard to parse.
Paleobiologist Philip Wilby and colleagues at the British Geological Survey discovered the new fossil in the Charnwood Forest, a hotbed of pre-Cambrian paleontology in a hilly area of Leicestershire in central England. They dated the rocks surrounding the fossil to between 556 million and 562 million years ago using the radioactive decay of uranium into lead.
The 20-centimeter fossil—about as long as a dinner fork—is an impression of a two-pronged creature with long stems topped by cups with tentacles. The organism appears to be in its polyp stage, the life cycle when a cnidarian adheres to the ocean floor and uses its tentacles to grab tasty larvae and floating plankton. The body of A. attenboroughi has fourfold symmetry, meaning it’s symmetrical around all four corners of a center point, as are modern jellyfish.
The researchers made a cast and a detailed drawing of the fossil, which they viewed and manipulated on a computer to better view the creature in different lighting. They then used another computer program to tally the fossil’s physical traits and place it on an evolutionary tree.
The team concluded that A. attenboroughi is a cnidarian and a member of the subgroup called medusozoans, which contains modern jellyfish, they report today in Nature Ecology & Evolution. If true, “our fossil becomes the oldest animal with direct living descendants in the fossil record—full stop,” Dunn says.
“It’s more akin to a modern animal group than anything else of this age or older,” agrees Alexander Liu, a paleobiologist at the University of Cambridge who was not involved with the new find; he was part of the team that described Haootia in 2014. Still, he wishes the authors had more closely compared the new fossil with groups like the coral-containing cnidarian subgroup anthozoans.
As for the creature’s alliterative name, the researchers chose Auroralumina because of its status as an early animal and because the shape reminded Dunn of the Olympic torch; in Latin, aurora means dawn, and lumina means light. And they chose attenboroughii because Attenborough spent his childhood near Charnwood and has brought attention to its fossils. “He grew up stomping over those ancient woodlands, so we wanted to name the species after him,” Dunn says.
Source: Science Mag