Scientists believe they can trace the first animals that roamed the Earth to about 700 million years ago, according to a new study published in Nature.
Researchers have determined that the first animal was likely a comb jelly, or stenophore — a predator that travels through the ocean in search of food, according to a news release on the study from the University of California, Berkeley.
Although they resemble jellyfish, comb jellies are distinctly different creatures and propel themselves through the water using cilia instead of tentacles. They are still part of marine ecosystems today and are found in waters around the world.
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“The most recent common ancestor of all animals probably lived 600 or 700 million years ago. It’s hard to know what they looked like because they were soft-bodied animals and don’t leave a direct fossil record,” said Daniel Rokhser, a UC. Berkeley professor and co-author of the study, in a statement. “But we can use comparisons between living organisms to learn about our common ancestors.”
There has been a long-standing debate over which animal came first — the ctenophore or the sponge, the university said. Sponges are animals that spend most of their lives in one place, filtering water through their pores to collect food particles.
Many have argued that because of the sponge’s primitive properties, it came first — before the cenophores, the researchers said. This new study determined that while sponges came early, they were probably second only to cenophores.
To make this decision, scientists looked at the organization of genes on the organism’s chromosomes. Cenophores’ chromosomes look very different from the chromosomes of sponges, jellyfish and other invertebrates — warning researchers that cenophores may have arrived either earlier or much later than others.
“At first, we couldn’t tell whether ctenophore chromosomes were different from other animals because they have changed so much over millions of years,” Rokhsar explained in the news release. “Alternatively, they may have diverged because they branched off first, before all the other animal lineages arose. We have to figure that out.”
There was a “smoking gun” for the researchers when they compared the chromosomes of ctenophores to those of non-animals.
“When the team compared the chromosomes of these diverse animals and non-animals, they found that ctenophores and non-animals shared specific gene-chromosome combinations, while the chromosomes of sponges and other animals were rearranged in a distinctly different manner.” said the release.
According to the researchers, the new insights are valuable for learning about the basic functions of all animals and humans today, such as how we eat, move and sense our surroundings.