As if dreamed up by Jules Verne himself, a new creature described only by its fossilized remains is lending a new perspective to the ordering of the Tree of Life.
What are now rice fields and farmlands in China’s Yunnan Province, half a billion years ago once made up the seafloor – home to mysterious and monstrous creatures like the Daihua sangiong that attached itself to the seafloor and had 18 feathery, prey-capturing tentacles around its mouth. According to research published in Current Biology, the animal could be an ancient cousin that set the stage for one of the world’s most radiant sea-dwelling creatures: ctenophores.
All living creatures evolved from a single common ancestor, study author Jakob Vinther told IFLScience, adding that studying fossils is an important part of tracing evolutionary history and understanding where modern animals came from – particularly the peculiar ones.
Repeated dark stains along each tentacle of D. sangiong resemble how comb jelly combs fossilize, explained Vinther. The fossil also preserves visible rows of cilia that have only previously been found in comb jellies across the Tree of Life.
Not to be confused with jellyfish, comb jellies come from an entirely different phylum and have been the source of contention among evolutionary biologists for more than 150 years. Comb jellies were among the first animals to evolve, and today use a band of iridescent, brightly colored “combs” along their body that are packed with cellular protrusions called cilia, which they use for locomotion.
"We can trace the gelatinous comb jellies back to ancestors with a skeleton and further back to ancestors that sat on the seafloor [with] flower-like bodies," Vinther told IFLScience.
The researchers drew their conclusions after noticing that D. sangiona resembles another tulip-shaped ocean animal called Dinomischus that was discovered at Burgess Shale in Western Canada. Similarly, Dinomiscus swam through the world’s oceans around 508 million years ago with 18 tentacles and an organic skeleton. Another fossil known as Xianguangia may have evolved into today’s comb jellies, rather than sea anemones, suggest the authors.
"This shows that they have similarities to the cnidarians, where sea anemones and jellyfish belong," explained Vinther.
Under this theory, comb jellies evolved with an organic skeleton. Their namesake combs come from their ancestors’ tentacles that were once attached to the seafloor, write the authors. Their mouths may have then expanded into balloon-shaped spheres, while their bodies became smaller until their tentacles moved from around their mouth to their backside.
This new phylogenetic analysis positions them alongside sponges as being the sister group of all animals, but not everyone is convinced. Ecology and evolutionary biologist Casey Dunn told Live Science that while D. sanqiong’s discovery is impressive, he is “highly skeptical” of conclusions drawn by the research team – and others agree.
"This paper strikes me as seeing the webbed feet and bill of a platypus and saying it must be a duck, (despite the fact that) it doesn't fly like a duck, or quack like a duck,” Monterey Bay Aquarium biologist Steven Haddock told National Geographic. "To those familiar with modern comb jellies, the purported correspondence with (these) fossils is equally fanciful."
The authors, on the other hand, believe their findings make a strong case for repositioning the comb jelly back alongside corals, sea anemones, and jellyfish.