As shown in the image above: This is a fragment of a three-dimensional sponge skeleton from a modern keratin sponge, showing its branches and fiber networks.
Based on fossils that may be the oldest animal samples on Earth, sponges hanging in your bathroom may date back nearly 1 billion years to an evolutionary lineage.
These 890 million-year-old fossils, possibly ancient sponges, were found in the Northwest Territories of Canada, with their tiny, slender branching tendrils invisible to the naked eye. But under the microscope, the preserved organic tissue shows a reticulated structure that bears a striking resemblance to the skeleton fibers of modern bathroom sponges. This is part of a soft sponge called a keratinous sponge or sponge.
<h1 class="pgc-h-arrow-right" data-track="33" > these fossils predate the second oldest sponge fossil by 350 million years</h1>
Paleontologists have thought sponges are good candidates for the earliest animal life. If this analysis is correct, Canadian fossils do represent ancient sponges, which would be about 350 million years older than the oldest known sponge fossils, according to a new study.
Elizabeth Turner, a professor of carbonate sedimentology and invertebrate paleontology at Laurentian University in Ontario, Canada, said she first noticed the strange fossils in the early 1990s, when she was examining samples of huge fossil reefs built from ancient cyanobacterial bacteria.
"When I looked at the flakes of rock through a microscope, I saw something much more complex than cyanobacterial bacteria in some of the samples," Turner said. I think it looks a bit like a sponge fossil from a younger rock. ”
But sponges weren't her focus at the time, so she put the odd fossils on hold for the time being until years later, when she returned to the area to collect more samples. By then, other scientists had published descriptions of fossil sponge bones, which reinforced Turner's skepticism about her unusual discovery.
Turner said: "If you look at the body of a sponge fossil with a microscope, you will find that it has this unique microstructure, which is completely related to the sponge protein (a type of collagen) skeleton in modern keratinized sponge fossils." Its structure is the same as the fossils I found. ”
As shown in the image above: The preserved tissue may belong to an ancient sponge from 890 million years ago.
It makes sense to find sponge fossils in cyanobacterial reef fossils, as such reefs would produce a lot of oxygen.
Turner explains: "Even if sponges can't compete with cyanobacteria for a spot on the ocean floor, they may settle in some parts of the reef where they can reap the benefits of oxygen plants." Cyanobacterial bacteria can also feed sponges, shed polysaccharides from their cell walls to nourish them, and fill the water around coral reefs with nutrient-rich suspended snot.
She added: "There are plenty of good reasons why sponges may be living in the environment where I found these hypothetical sponge fossils." ”
In January, media reported that the fossils' offshoot tendrils did resemble ancient fungi in some way, and as can be seen in fossils described earlier this year, this is the oldest evidence of a terrestrial fungus dating back 635 million years. But Turner ruled out fungal identity for the newly discovered fossils, as the fibers in fossils and modern sponges branched out and reconnected into a three-dimensional network. This makes them distinctly different from the fungal branches, which are joined together at right angles.
Joachim Reitner, a professor at the Geosciences Centre at the University of Geosciences at the University of Geosciences in Germany, said: "Turner's findings are very special for this type of keratinized sponge. ”
Reitner said: "This substance, which we call sponge protein, is a complex protein compound. It is very resistant to microbial degradation, which is why we have these networks of sponge fibers in the fossil record. This type of network is a characteristic of sponges, and you can classify the types of sponges according to the network of sponges. No other creature can do that. ”
As shown in the image above: Paleontologist Elizabeth Turner found these fossils in ancient coral reefs built of cyanobacterial bacteria in the Northwest Territories of Canada.
<h1 class="pgc-h-arrow-right" data-track="18" > earliest animal</h1>
When did the first animals on Earth appear? Before 580 million years ago, there was little physical evidence of the existence of animals, but that doesn't mean they didn't exist, as mollusks usually don't turn into fossils very well.
Preserved molecules or biomarkers, thought to be endemic to animals, are one of the clues to the study of ancient animal life. In 2018, according to media reports, traces of cholesterol in a fossil dating back 558 million years allowed researchers to identify a strange mollusk called the Dickinson jellyfish.
More than a decade ago, scientists found fossil traces of fatty compounds or sterols from ancient sponges 635 million years ago, which appear to be the oldest known animal sample. However, in two studies published in 2020, the researchers revisited the claim and found that the sterols described in 2009 were most likely produced by decaying algae, rather than by animals.
<h1 class="pgc-h-arrow-right" data-track="24" > an important discovery</h1>
David Bottjer, a professor of earth sciences at the University of Southern California in the United States, said: "When physical fossils are scarce, scientists who study the evolutionary history of the earth often turn to molecular clocks. ”
"By assessing DNA differences and mutation rates in modern organisms, molecular clock methods can estimate when animals in a particular population may have begun to evolve," Burt said. According to this approach, organisms are thought to appear at a much older age than the fossil record represents, turner wrote in the study, and new discoveries support this conclusion.
Turner said: "If my interpretation of these materials is correct, then animals have appeared long before traditional animal fossils appeared, and they have a long prehistoric history." ”
The oldest unquestionable sponge fossils are mineralized needles, and pointed structures have been found in many types of sponges. In April, another team of researchers described needle-like fossils from about 535 million years ago, dating back to before the Cambrian Period (543 million to 490 million years ago). But the molecular clock method has long shown that sponges are much older than that, and Turner's study provides the first physical evidence of how old sponges really are.
Although needles are the most common fossil marker for sponges, many modern sponges do not have needles, and the discovery of a sponge that may be 890 million years old and has this characteristic is an important discovery.