The protein skeleton from an ancient sponge E.C. is revealed by microscopic calcite structures Turner
350 million years ago, the origin of animals could have occurred 350 million more years before it was thought. From 890 million years ago, rocks contained fossils that appear to be sponges. This is one of the earliest animals to have evolved.
Elizabeth Turner, a Canadian student at Laurentian University, Sudbury, made the discovery. She says that the fossils she discovered fit in with other evidence.
Animals are multicellular organisms that are mostly made up of distinct tissues. They must eat food to survive, which is not the case with plants. The Cambrian Period (541 million years ago) has been the home of the oldest known animal fossils. Recent years have seen some fossils from earlier Ediacaran Period (635-541 million years ago), being identified as animals. Chemical traces dating back to 660 million years ago that could be from sponges are also found.
Turner examined rocks in north-west Canada that held the remains of reefs dating back to 890 million years ago during the Tonian period. These reefs were not made of corals like modern reefs. They were instead made from photosynthetic bacteria that live in shallow waters. These reefs, also known as stromatolites were many kilometres in length and reached heights of hundreds of meters above the seafloor. Turner says these are amazing reefs.
Turner discovered the remains of a network made up of fibres that branched out and connected in a complex web within the rocks. These are not normal fossils but sponge remains, Turner argues.
Modern sponges have a mesh of a protein called Spongin that forms a soft skeleton. Turner's research suggests that the soft tissues of ancient sponges became mineralized when they died, while the hard spongin did not. It eventually began to decay, leaving behind hollow tubes in the rock, which were later filled with calcite crystals. Turner found these networks of calcite (pictured right) and the way they branched looked exactly like spongin.
The E.C. sponge skeleton is made of spongin Turner
Joachim Reitner, a German researcher who has studied preserved sponges, said that similar fossils from later times have been convincingly identified to be sponges. This network is unique and has been created by no other organisms.
This was something that I found convincing. Amelia Penny, University of St Andrews in UK.
Origins in the early days
Sponges must have existed 890 million year ago to explain how animals evolved. Modern DNA has been used to calculate when the key events of evolution took place in molecular clock studies. They have shown that animals evolved long before fossils. This approach is less reliable when there isn't enough fossils to calibrate it. Penny says Turner's discovery brings the fossil record in line with molecular clock estimates.
Two key elements of the Earth's history are altered by an earlier origin of animals. First, oxygen levels were low until they increased between 800 and 540 millions years ago. The evolution of animals is believed to have been enabled by this increase in oxygen. However, Turner says that animals existed as early as 890 million years ago and that it would be possible for them to survive without much oxygen. Reitner also says that many modern sponges can survive in low-oxygen environments.
Second, the majority of the planet became a snowball Earth between 720 and 635 millions years ago. Penny says that these were previously thought to be catastrophic events for Earth's multicellular life. It seems that sponges survived the glaciations.
They didn't wipe out all of the products of biological evolutionary evolution to date. Life did not have to restart from scratch because the things that I have identified are almost identical to sponge fossils [from a much later time period], says Turner.
Sponges vs comb jellies
The question remains as to which animal groups emerged first. Although most paleontologists believe that sponges are the first to emerge, genetic studies over the past decade have shown that comb jellies that look very much like jellyfish were actually more recent. This debate is still ongoing. Penny would only suggest that the discovery of early sponges does not mean that there weren't also comb jelly very early. These soft-bodied animals are seldom preserved.
Journal reference: Nature, DOI: 10.1038/s41586-021-03773-z
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