It was the first animal to appear on earth

A sponge, no matter how much you look at it from every angle, it will always look ancient to you. She has no nerve or muscle. And it usually spends its life almost motionless, foraging for food particles that filter through seawater. That is why it has long been considered the ancestor of all animals living on Earth.

But, twist! researchers The University of California (USA) and the University of Vienna (Austria) have discovered that cetenophores, carnivorous and transparent sea creatures similar to jellyfish, were actually the first animals to appear on our planet. That was half a billion years ago.

Ctenophores as the common ancestor of animals

Of such delicate animals, fossils are unlikely to be found to date. The researchers had to go to a sharp analysis of the structure of their chromosomes. To understand, you need to know that biologists have previously been able to establish that sponges, jellyfish and some other invertebrates have identical genes. Half a billion years of free evolution have passed. They concluded that chromosomes evolve slowly. They were thus able to reconstruct the chromosomes of the common ancestor of these animals.

In parallel, researchers have determined the structure of ctenophores chromosomes. A very different structure from other invertebrates. But they don’t know if this means that cetophores evolved recently or, conversely, branched off first. Finally, it was only when they compared the chromosomes of ctenophores to the chromosomes of non-animals that biologists understood. Because non-animals exhibited xenophore-like arrangements. For the researchers, the simplest explanation is that ctenophores branched off before the reorganizations that led to sponges.