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The oldest index of animal life, dating back at least 100 million years before the Cambrian period, at the time of appearance of most major types of animals, was discovered by researchers at the University of California, Riverside (UCR).
The researchers followed molecular signs of animal life, called biomarkers, already 660 to 635 million years ago during the Neoproterozoic era. They discovered a steroid compound produced only by sponges, which are part of the oldest forms of animal life, in ancient rocks and oils from Oman, Siberia and India.
The identified biomarker, a steroid compound called 26-methylstigmastane (26-mes), has a unique structure whose synthesis is currently known to be synthesized only by some modern sponge species called demosponges.
The study, led by Gordon Love, a professor in the UNR Department of Earth Sciences, was published today in Nature Ecology & Evolution.
"This biomarker of steroids is the first evidence that demosponges, and thus multicellular animals, thrived in ancient seas at least 635 million years ago," said Alex Zumberge, author of the study. , and a PhD student working in Love Group research.
Alex Zumberge of the University of California at Riverside (right) collects 750 million year old rocks from a lake outcrop in Sweden. (Photo credit: UC Riverside)
This discovery is the result of the search for evidence of molecular fossils rather than conventional fossils.
"Molecular fossils are important for tracking the first animals, because the first sponges were probably very small, did not contain a skeleton, and did not leave well-preserved or readily recognizable body records," said Zumberge. "We were looking for distinctive and stable biomarkers that indicate the existence of sponges and other primitive animals, rather than unicellular organisms that dominated the Earth for billions of years before the dawn of a complex and multicellular life.
Read the study "The Demosponge 26-methylstigmastane Demographic Biomarker Provides Evidence for Neoproterozoic Animals" to Nature Ecology & Evolution.
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