Sea sponges were widely thought to have been the first animals on earth. However, in recent genetic research the humble comb jelly was suggested to have claimed the title. But in a new study from MIT, sea sponges have retained its position.
In new genetic analyses, it has been confirmed that sea sponges are the source of a curious molecule that has been found in rocks that are 640 million years old. These rocks considerably predate the Cambrian explosion, which is the period believed when most animal groups had taken over the planet, around 540 million years ago.
Lead author David Gold, a postdoc in MIT’s Department of Earth, Atmospheric and Planetary Sciences (EAPS), along with senior author and EAPS Professor Roger Summons, suggest that it is for this reason that sea sponges may have been the first animals to inhabit the Earth, saying that:
“We brought together paleontological and genetic evidence to make a pretty strong case that this really is a molecular fossil of sponges. This is some of the oldest evidence for animal life.”
According to MIT news:
“Paleontologists have unearthed an extraordinary number of fossils from the period starting around 540 million years ago. Based on the fossil record, some scientists have argued that contemporary animal groups essentially “exploded” onto Earth, very quickly morphing from single-celled organisms to complex multicellular animals in a relatively short geological time span.
“However, the fossils that are known from before the Cambrian explosion are peculiar in many respects, making it extremely difficult to determine which type of animal was the first to the evolutionary line.
“Summons’ lab has been looking for the answer in molecular fossils — trace amounts of molecules that have survived in ancient rocks long after the rest of an animal has decayed away.”
Watch this video from Massachusetts Institute of Technology (MIT) on their discovery:
“There’s a feeling that animals should be much older than the Cambrian, because a lot of animals are showing up at the same time, but fossil evidence for animals before that has been contentious.
“So people are interested in the idea that some of these biomarkers and chemicals, molecules left behind, might help resolve these debates.”
Previous research had identified one chemical in particular, 24-isopropylcholestane (or 24-ipc for short), which is a lipid molecule, or sterol, a modified version of cholesterol. In 1994 a team led by Mark McCaffrey PhD, which Summons was involved with, found 24-ipc in abnormally high amounts in Cambrian and slightly older rocks.
The researchers then speculated that sponges or their ancestors may be the source.
Another research team in 2009 confirmed the existence of 24-ipc in 640-million-year-old rock samples from Oman. Because of the age of these rock samples, the research team suggests this potentially represents the oldest evidence for animal life.
According to the Mother nature network:
“To assemble the puzzle of what kinds of animals might have produced this 24-ipc, researchers turned to genetic analysis. They surmised that if they could identify the gene responsible for making 24-ipc and find the organisms that carry this gene, they could trace when the gene evolved in those organisms.
“The gene they identified, it turns out, is found in just the right form in both sponges and some types of algae. Researchers then performed genetic analysis to determine whether sea sponges or algae had evolved this gene first. The results were definitive: it was the sponges. Even more telling, the genetic analysis revealed a rough date for when the gene likely first appeared among sponges: 640 million years ago.”
All the pieces of the puzzle fit together offering a convincing case that the sponge, or some expression of a sponge-like creature, was the first animal to inhabit the planet.
The results from the MIT led research was published in the Proceedings of the National Academy of Sciences.