The ancestor of all modern animals

It looks like a little worm. It is no bigger than a grain of rice. And yet it is an impressive discovery. It happened in Australia. A team of geologists has discovered the ancestor of all modern animals. Yes, including humans. It is called Ikaria wariootia. It is the first bilateral, that is, the first organism with a front and rear part. It has two symmetrical sides and openings at each end (mouth and anus) connected by an intestine. The finding was published Monday in the journal Proceedings of the National Academy of Sciences (PNAS).

This is a theoretical representation of the ancestor of all modern animals
This is a theoretical representation of the ancestor of all modern animals

The first multicellular organisms had variable shapes. It is known as the biota of the Ediacaric period. And this group contains the oldest fossils of complex, multicellular organisms. But most are not related to current animals. A famous example is the water lily-shaped creatures known as Dickinsonia. They lack the basic characteristics of most animals, such as the mouth or intestine.

What bilateral symmetry gave us

The development of bilateral symmetry was a critical step in the evolution of animal life. It gave organisms the ability to move with determination and a common and successful way of organizing their bodies. As the authors explain, a multitude of animals, from worms to insects, from dinosaurs to humans, organize around this same basic plan of the bilateral body.

Evolutionary biologists predicted that the ancestor of all modern animals must have been simple and small. He must have had rudimentary sense organs. Preserving and identifying the fossilized remains of such an animal was thought to be nearly impossible.

Until Scott Evans and Mary Droser of Riverside discovered tiny, oval prints near some of some fossilized burrows. It was in Nilpena, South Australia. They used a three-dimensional laser scanner. It revealed the regular and consistent shape of a cylindrical body. It had a different head and tail and slightly ribbed musculature.

"Once we had the 3D scans, we knew we had made an important discovery," said Evans.

These are the stone impressions of Ikaria wariootia.
These are the stone impressions of Ikaria wariootia.
Complex for your time

Ikaria It was complex compared to other fossils from this period. It was buried in thin layers of well-oxygenated sand at the bottom of the ocean in search of organic matter. That indicates rudimentary sensory capacities. The depth and curvature of Ikaria they represent clearly different front and rear ends.

The burrows also retain the transverse "V" ridges. That suggests Ikaria was moving by contracting muscles through her body like a worm. This is called peristaltic locomotion. Evidence that the organism fed on buried organic matter reveals that the creature probably had a mouth, anus, and intestine.

"This is what evolutionary biologists predicted," says Droser. It is really exciting that what we have found so clearly aligns with your prediction. ”

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