Researchers have identified that this animal could be the comb jelly – a predatory species found throughout the oceans, according to a study from the University of California, Berkeley.
Although it resembles a jellyfish, comb jellies are an entirely different type of organism and propel themselves through water using tiny hair-like structures instead of tentacles. They continue to play a role in today’s marine ecosystem and can be found in oceans around the world.
Comb jelly in the Red Sea. (Photo: Getty).
“The most well-known ancestors of all these animal species probably lived around 600 to 700 million years ago. It’s hard to know what they looked like because they were soft-bodied and left no direct fossil traces. However, we can compare living species to learn about their ancestors,” said Professor Daniel Rokhsar of UC Berkeley and co-author of the study.
Today, Earth is home to countless animals of all shapes and sizes, from tiny tardigrades to 25-meter-long blue whales. These organisms have appeared and evolved over millions of years. The question of which animal appeared first on Earth has sparked intense debate among scientists. Dozens of different studies, using everything from chromosomal evolution over time to ancient fossils, have proposed two main candidates: sponges and comb jellies, according to Live Science.
Many believe that due to the primitive characteristics of sponges, they emerged first, even before comb jellies. However, recent research has determined that while sponges appeared early, they may have actually come after comb jellies. To reach this conclusion, scientists examined the genetic organization in the chromosomes of these organisms. The chromosomes of comb jellies are vastly different from those of sponges, jellyfish, and other invertebrates, suggesting they may have appeared much earlier or later than other species.
Researchers compared the chromosomes of comb jellies with those of non-animal organisms and found that they share some combinations of genetic material, while the chromosomes of sponges and other animal species are arranged in a completely different manner.
Some information about the earliest animals comes from fossils dating back to the Cambrian period, which began about 541 million years ago. During this time, Earth experienced an explosion of new species. In just 10 million years, hundreds of thousands of animal species suddenly appeared. Nearly every type of body structure of animals that exists today evolved during the Cambrian explosion, including arthropods, mollusks, and early chordates, which eventually led to vertebrates. Specimens found in the Burgess Shale formation in British Columbia provide insights into the shapes of primitive animals.
Comb jellies propel themselves through water using tiny hair-like structures instead of tentacles.
However, not all animals appeared suddenly. In the 1950s, previously discovered fossils were identified as Ediacaran organisms, which existed from about 635 million years ago until the start of the Cambrian period 541 million years ago. Unlike the hard exoskeletons found in many Cambrian fossils, Ediacaran animals primarily had soft, jelly-like bodies, along with sea pens, sea anemones, and sponges. Soft tissue is extremely difficult to preserve because it decomposes more easily than bone or exoskeletons. This means that fossils of Ediacaran animals are not only scarce but also challenging to analyze. A prime example of these is a worm-like creature called Dickinsonia, resembling a large disc with many tentacles radiating from its center.
Elizabeth Turner, a paleobiologist at Laurentian University in Ontario, proposed in 2021 in the journal Nature that the oldest known animal is a fossilized sponge dating back 890 million years. However, not all experts agree with her hypothesis.
All the evidence mentioned regarding the earliest animals comes from fossils in rocks that can be dated through their isotopes, which decay at a steady rate over time. Recently, a new method using a model called molecular clock has become increasingly popular. Based on the assumption that genes mutate at a consistent rate over time, scientists can analyze the genomes of modern animals to estimate when they first appeared. A 2023 study using chromosomal data from comb jellies suggested that they are the earliest animals, appearing around 600 to 700 million years ago.
However, Nick Butterfield, a paleobiologist at the University of Cambridge, expressed skepticism towards both hypotheses. If animals existed 890 million years ago, we would expect to see traces such as biomineralization, where molecules from the organic material of animals could cause surrounding minerals to crystallize. Yet the oldest known biomineralization dates back only 750 million years.
The ancestor of all modern animals is an unexpected species
