Fossils found in the rugged mountainous terrain of Canada’s Northwest Territories may provide a glimpse into the humble dawn of animal life on Earth – sea sponges that inhabited primordial reefs built by bacteria around 890 years ago. million years ago.
A Canadian researcher said on Wednesday that the fossils, dating from a time known as the Neoproterozoic period, appeared to show distinctive microstructures of the body of a sea sponge constructed in the same way as a living species today known as the Mediterranean bath sponge. , or Spongia officinalis.
If this interpretation is correct, it would be the oldest fossils of animal life around 300 million years old.
“The first animals to emerge in evolution probably looked like sponges. This is not surprising given that sponges are the most basic type of animal both today and in the fossil record, ”said geologist Elizabeth Turner of Laurentian University in Canada, who led study. published in the journal Nature.
The Earth was formed over 4.5 billion years ago. The earliest forms of life were bacteria-like, single-celled marine organisms that appeared hundreds of millions of years later. Complex life evolved relatively late in Earth’s history.
The first appearance of rudimentary animal life was a much debated topic in terms of timing and form. An enigmatic ribbed, pancake-shaped organism called Dickinsonia, known from fossils dating back to around 575 million years ago, has been considered the earliest known animal.
Turner said she believed the animals evolved much earlier than current fossil records indicate.
“The existence of a long history back is not surprising, but its length – a few hundred million years – may be a bit unexpected for some researchers,” said Turner.
When people think of animals, a sponge may not immediately come to mind. But sponges – aquatic invertebrates that live attached to the sea floor and have soft, porous bodies with internal skeletons – are among the top performing groups of animals.
“They don’t have a nervous, digestive and circulatory system. They have an incredible water pumping machine, produced by specialized cells, which they use to move seawater around their bodies to filter, ”Turner said.
Some sponges have skeletons made of microscopic rods of quartz or calcite. Others have skeletons made up of a resistant protein called spongin that forms a complex three-dimensional mesh supporting the soft tissue of the animal. Canadian fossils represent the latter type, called a horny sponge.
“It’s the relic structure of the 3D mesh spongine skeleton that is preserved and that is so distinctive,” said Turner.
This structure, visible under a microscope, is made up of tiny tubes that branch out and come together to form the mesh. The size of the body of the sponge would have been approximately four tenths of an inch (1 cm). Turner said the sponges appear to have lived in cavities just below the surface of the reef and in surface depressions.
If these fossils truly show a type of sponge, their age would indicate that Earth’s earliest animals evolved before a pair of landmark events generally considered to predate animal life.
One of them was the second of two episodes in the history of the planet where the amount of atmospheric oxygen increased considerably, some time between 830 and 540 million years ago. The other was an extremely cold period where the Earth may have been covered with ice or at least partially frozen, some time between 720 and 635 million years ago.
The fossils predate what were the earliest known sponge fossils by about 350 million years. Turner noted that genetic research indicates that sponges first appeared around the time these fossils date. Reuters