Fossil Steroids Record the Advent of Earliest Known Animals
Demosponges appeared 635 million years ago in era of climatic extremes and evolutionary developments
Using compounds preserved in sedimentary rocks more than 635 million years old, researchers have found some of the earliest evidence for the existence of animals.
Demosponges thrived in the shallow coastal waters of what is now Oman, according to scientist Gordon Love of the University of California at Riverside and colleagues from MIT and other institutions.
They report the results of their research in this week's issue of the journal Nature.
"Demosponges appeared during the Neoproterozoic era, 1,000 to 542 million years ago, an era of climatic extremes and biological evolutionary developments culminating in the emergence of animals and new ecosystems," said Love.
"These sponges currently represent the oldest evidence for animals in the fossil record."
The preserved compounds Love and colleagues discovered in these sponges, called steranes, exist in a wide variety of biochemical configurations, according to Stephen Macko, program director in the National Science Foundation (NSF)'s Division of Earth Sciences, which funded the research.
"The compounds are also known as 'biomarkers,' indicating that they can be traced directly to living organisms," said Macko.
The biomarker Love and colleagues identified, 24-isopropylcholestane, is found in living demosponges, and now has been observed in 635 million-year-old rocks, but was not seen in older samples of the same rock formation.
"The fact that these biomarkers were found in samples associated with sedimentary rocks that formed in shallow waters," said Macko, "lends support to the hypothesis that demosponges arose in warm shallow coastal seas."
Feeding on dissolved and particulate organic debris in the water, these animals eventually migrated to the deep sea. They now reside there, as well as in shallower coastal waters.
The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2016, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards. NSF also awards about $626 million in professional and service contracts yearly.
Useful NSF Web Sites: