Surprising discovery of the oldest living creature on Earth

Scientists have confirmed that creatures called ctenophores lived on our planet 700 million years ago.

Jellyfish-like creatures called ctenophores first appeared 700 million years ago, much older than dinosaurs, which appeared 230 million years ago.

A team of researchers from the University of California (USA) identified ctenophores as the closest relatives of the first animals on the planet. We can still find them swimming in the oceans and aquariums today.

In addition, this discovery also puts to rest the long-standing debate that sponges were the first animals because their fossils date back about 600 million years.

Ctenophores have eight sets of cilia, similar to tentacles, running down their sides. They are used to create propulsion when moving at depths of more than 6km below the surface of the oceans.

“The most recent common ancestor of all animals probably lived 600 to 700 million years ago,” said Daniel Rokhsar, a professor at the University of California and co-author of the study. “It’s hard to determine what they looked like because they were mollusks and didn’t leave fossils.”

For comparison, worms began evolving nearly 500 million years ago, and vertebrates appeared about 450 million years ago.

Together, they are known as bilaterally symmetrical creatures — with heads with centralized brains, guts running from mouth to anus, muscles and other common features — that evolved at the time of the famous “Cambrian Explosion” about 500 million years ago.

Although they resemble jellyfish in appearance, the two are only distantly related.

Unlike regular jellyfish, which zoom through the water, ctenophores propel themselves with nine rows of cilia arranged along the sides of their bodies like combs. Along the California coast, a common ctenophore is the gooseberry comb jelly.

Each species has a characteristic number of chromosomes – humans, for example, have 23 pairs – and a characteristic distribution of genes along the chromosomes.

Researchers have previously shown that the chromosomes of sponges, jellyfish and many other invertebrates carry some similar genes, despite having evolved independently for more than half a billion years.

This finding suggests that the chromosomes of many animals evolve slowly and allowed the team to reconstruct the chromosomes of the common ancestor of these diverse animals on a computer.

“At first, we couldn’t tell if ctenophores were different from those of other animals,” Rokhsar said. “They’ve changed so much over hundreds of millions of years. They might be different because they were the first branching off before all the other animal lineages appeared. We needed to figure that out.”

The researchers worked together to sequence the genomes of a comb jelly and a sponge, as well as three single-celled organisms outside the animal lineage: a choanoflagellate, a filasterean amoeba, and a fish parasite called an ichthyosporean.

Raw genome sequences of these non-animal species exist, but they do not contain the crucial information needed for gene linkage at the chromosome scale: chromosome location.

Remarkably, 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 way.

“We found some rearrangements in sponges and non-ctenophores,” says Professor Rokhsar. “In contrast, ctenophores are not animal-like. The simplest explanation is that ctenophores branched off before the rearrangements occurred.”

According to baotintuc.vn

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