The humble sea sponge may have been the first animal to ever develop on our planet, according to genetic analysis conducted on 640-million-year-old rocks.
According to scientists, there are approximately 8.7 million animal species on Earth. It is possible that the simple sea sponge was the first one, researchers at the Massachusetts Institute of Technology (MIT) in Cambridge said.
Sea sponges are animals of the phylum Porifera that have bodies full of channels and pores, which enable water to circulate through them. They do not have digestive, nervous, or circulatory systems and rely on the water flow through their bodies to get rid of wastes, and obtain oxygen and food.
The team of scientists conducted several genetic tests and found molecules produced by sea sponges in rocks that are 640 million years old. These rocks existed long before the Cambrian explosion – an evolutionary event, beginning around 542 million years ago in the Cambrian Period when most major animal phyla came into existence. Because of that, scientists suggest that sea sponges may have been the first ever animals.
In the new study – published Friday (Feb. 26) in the Proceedings of the National Academy of Sciences – the researchers wrote that the findings provide the oldest evidence for animal life.
David Gold, a post-doctoral researcher in the Department of Earth, Atmospheric, and Planetary Sciences (EAPS) at the Massachusetts Institute of Technology, said that he and his colleagues gathered both genetic and paleontological evidence, which showed that the 640-million-year-old rocks contained molecular fossils of sponges.
For a while now, palaeontologists have tried to figure out which animal was the first in the evolutionary line.
Roger Summons, a professor of geobiology at MIT’s Department of Earth, Atmospheric, and Planetary Sciences and a fellow of the Royal Society, has spent more than twenty years to find an extended evolutionary tree of the animal kingdom. To do so, he and fellow researchers have focused on molecular fossils, which they gathered from various ancient rocks.
In 1994, scientists first speculated about the sponge biomarker hypothesis. They were able to partially confirm it by 2009. Researchers at the Massachusetts Institute of Technology said that the sponge biomarker hypothesis focuses on traces of the chemical 24-isopropylcholestane – which is a lipid molecule that was found in high amounts in rocks from the Cambrian period, and even in slightly older rocks.
According to Dr. Summons, the genetic testing conducted by David Gold is another piece of evidence which suggests that sponges or their ancestor may have been the first animals on Earth.
Based on the new findings, sea sponges likely appeared on our planet about 640 million years ago, or perhaps even earlier than that, the researchers said. However, a lot of questions still remained unanswered: In what environment did the creatures live in? What did they look like? Why are there big gaps in the fossil record?
There are still a lot of discoveries to be made about early animal life on Earth, Dr. Gold said. Perhaps those molecular fossils will one day help fill in the gaps, he added.
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