Ancestor of 'all living creatures' dug up in Australia

The daddy of all living creatures has been discovered in Australia.

That’s not an understatement – scientists genuinely believe they’ve found a fossil of the ancestor of every living creature on Earth.

The tiny worm-like creature lived more than 555 million years ago, according to geologists who made the find.

They say it the first ancestor on the family tree that contains most familiar animals today, including humans.

Named Ikaria wariootia, it is the earliest bilaterian, or organism with a front and back, two symmetrical sides, and openings at either end connected by a gut.

Scientists explained that the earliest multicellular organisms – such as sponges and algal mats – had variable shapes.

Collectively known as the Ediacaran Biota, the group contains the oldest fossils of complex, multicellular organisms.

But most of them are not directly related to animals around today, including lily pad-shaped creatures known as Dickinsonia that lack basic features of most animals, such as a mouth or gut.

Scientists say the development of bilateral symmetry was a critical step in the evolution of animal life, giving organisms the ability to move purposefully and a common, yet successful way to organise their bodies.

A multitude of animals, from worms to insects to dinosaurs to humans, are organised around the same basic bilaterian body plan.

Evolutionary biologists studying the genetics of modern animals predicted the oldest ancestor of all bilaterians would have been simple and small, with ‘rudimentary’ sensory organs.

Preserving and identifying the fossilised remains of such an animal was thought to be difficult, if not impossible.

For 15 years, scientists agreed that fossilised burrows found in 555 million-year-old Ediacaran Period deposits in Nilpena, South Australia, were made by bilaterians.

But there was no sign of the creature that made the burrows.

Scott Evans, a recent doctoral graduate from University of Caifornia, Riverside, and Professor Mary Droser noticed miniscule, oval impressions near some of the burrows.

With funding from a Nasa exobiology grant, they used a three-dimensional laser scanner that revealed the regular, consistent shape of a cylindrical body with a distinct head and tail and faintly grooved musculature.

The creature ranged between two and seven millimetres long and about one to 2.5 millimetres wide, with the largest the size and shape of a grain of rice – just the right size to have made the burrows.

Dr Evans said: ‘We thought these animals should have existed during this interval, but always understood they would be difficult to recognise.

‘Once we had the 3D scans, we knew that we had made an important discovery.’

Ikaria wariootia was named to acknowledge the original ‘custodians’ of the land. The genus name comes from Ikara, which means “meeting place” in the Adnyamathanha language.

It’s the Adnyamathanha name for a grouping of mountains known in English as Wilpena Pound.

The species name comes from Warioota Creek, which runs from the Flinders Ranges to Nilpena Station.

Prof Droser said: ‘Burrows of Ikaria occur lower than anything else.

‘It’s the oldest fossil we get with this type of complexity. Dickinsonia and other big things were probably evolutionary dead ends.

‘We knew that we also had lots of little things and thought these might have been the early bilaterians that we were looking for.’

In spite of its relatively simple shape, Prof Droser explained that Ikaria was complex compared to other fossils from this period.

She said it burrowed in thin layers of well-oxygenated sand on the ocean floor in search of organic matter, indicating rudimentary sensory abilities.

The depth and curvature of Ikaria represent clearly distinct front and rear ends, supporting the directed movement found in the burrows.

Prof Droser said the burrows also preserve crosswise, “V”-shaped ridges, suggesting Ikaria moved by contracting muscles across its body like a worm, known as peristaltic locomotion.

She explained that evidence of sediment displacement in the burrows and signs the organism fed on buried organic matter reveal Ikaria probably had a mouth, anus, and gut.

Prof Droser added: ‘This is what evolutionary biologists predicted.

‘It’s really exciting that what we have found lines up so neatly with their prediction.”

The findings were published in the journal Proceedings of the National Academy of Sciences.

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