Ancestor of all animals identified in Australian fossils

Artistic rendering of Ikaria wariootia. Credit: Sohail Wasif / UCR

The team, led by geologists at the University of California at Riverside, discovered the first ancestor on the family tree, which contains the most famous animals to date, including humans.

A tiny worm-shaped creature named Ikaria wariootiaThis is the earliest Bilaterian or organism with the front and back sides, two symmetrical sides and holes at both ends connected by the intestine. Article published today in Proceedings of the National Academy of Sciences,

The earliest multicellular organisms, such as sponges and algae mats, were variable in shape. Collectively known as Ediacar biota, this group contains the oldest fossils of complex multicellular organisms. However, most of them are not directly related to animals today, including creatures in the form of lilies, known as Okkszszosha which lack the basic features of most animals, such as the mouth or intestines.

The development of bilateral symmetry was a critical step in the evolution of animal life, giving organisms the ability to purposefully move and a common but successful way to organize their body. Many animals, from worms to insects, from dinosaurs to humans, are organized according to the same basic two-sided plan of the body.

Evolutionary biologists studying the genetics of modern animals predicted that the oldest ancestor of all bilaterians would be simple and small, with rudimentary senses. The conservation and identification of the fossilized remains of such an animal was considered difficult, if not impossible.

Ancestor of all animals identified in Australian fossils

A three-dimensional laser scan that shows the correct, consistent shape of a cylindrical body with a distinct head and tail and weakly grooved muscles. Credit: Droser Lab / UCR

For 15 years, scientists have agreed that fossilized burrows found in sediments of the 555 million year old Ediacar period in Nilpen, South Australia, were made by Bilaterians. But there was no indication that the creature had burrowed, leaving the scientists only speculation.

Scott Evans, a recent UC Riverside doctoral graduate; and Mary Drozer, a professor of geology, noticed tiny oval prints next to some of these holes. Having received funding from a NASA exobiological grant, they used a three-dimensional laser scanner that showed the correct, consistent shape of a cylindrical body with a distinct head and tail and weak musculature. The length of the animal ranged from 2 to 7 millimeters, and the width was about 1-2.5 millimeters, and the largest in size and shape of the rice grain is just the size that burrows could make.

“We thought it was animals It should have existed during this interval, but always understood that it would be difficult to recognize them, Evans said. “After we carried out a three-dimensional scan, we knew that we had made an important discovery.”

Researchers, including Ian Hughes from the University of California at San Diego and James Gelling from the Museum of South Australia, describe Ikaria wariootianamed to recognize the original guardians of the earth. The name of the genus comes from Icarus, which means "meeting place" in the language of Adnamathanya. This is the name Adnyamathanha for a group of mountains known in English as Wilpena Pound. The name of the species comes from Warioota Creek, which runs from the Flinders Range to Nilpena Station.

Ancestor of all animals identified in Australian fossils

Ikaria wariootia impressions in stone. Credit: Droser Lab / UCR

"Burrows Ikaria occur lower than anything else. This is the oldest fossil we get with this type of complexity, ”said Drozer.Okkszszosha and other big things were probably evolutionary dead ends. We knew that we also had many little things, and thought that these could be the early Bilaterians we were looking for. ”

Despite its relatively simple form, Ikaria was complex compared to other fossils of this period. He dug in thin layers of oxygenated sand at the bottom of the ocean in search of organic matter, which indicates elementary sensory abilities. Depth and Curvature Ikaria clearly distinguishable front and rear ends supporting the directional movement found in burrows.

Burrows also retain cruciform, V-shaped ridges, suggesting Ikaria move by contracting muscles throughout the body, like a worm known as peristaltic locomotion. The data on the displacement of deposits in holes and the signs by which the body eats buried organic matter are revealed. Ikaria probably there was a mouth, anus and intestines.

“This is what evolutionary biologists predicted,” said Drozer. “It's really exciting that what we found is very accurately in line with their prediction.”

The study sheds light on the first animals of the Earth

Additional Information:
Scott D. Evans El All. “Discovery of the oldest Bilaterian from the Ediacar region of South Australia” PNAS (2020).

Ancestor of all animals identified in Australian fossils (2020, March 23)
restored March 23, 2020

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