First Animal on Earth Was Likely the Sea Sponge
A molecule in 640-million-year-old rocks, well before the Cambrian Explosion, comes from a simple sea sponge, according to new research from MIT.
Sea sponges, widely considered the first animals on Earth, now have some extra ammunition to back up that belief.
A molecule present in 640-million-year-old rocks comes from a simple sea sponge, according to genetic analysis done by Massachusetts Institute of Technology (MIT) researchers. The time frame is well before the Cambrian Explosion 540 million years ago, in which most animals groups sprang up and took hold in a relatively short geologic stretch.
That makes the humble sea sponge a likely bearer of the title "first animal on Earth."
That's according to findings appearing in a paper just published in the journal Proceedings of the National Academy of Sciences by lead author David Gold and senior author Roger Summons, both from MIT.
True to its name, the Cambrian Explosion produced no shortage of fossils. But very few pre-Cambrian samples exist. That paucity has made it difficult for scientists to determine which animal was first.
The MIT researchers decided to look for the elusive first creature by studying molecular fossils –- trace molecules still present in ancient rocks after the animal that left them has long since decayed into nothingness.
Gold and Summons focused on a particular molecule: 24-isopropylcholestane, or 24-ipc. It had been found, through prior research, in the 640-million-year-old rocks.
They suspected the molecule was from a sea sponge, as some modern sponges are known to produce it. But, the rub was that some forms of algae also make 24-ipc. So they had to prove the molecule came from a sea sponge, while ruling out algae.
The researchers first identified the gene that made the molecule, observing that sea sponges and algae have an extra copy of the gene.
Then, after some evolutionary-tree detective work, they traced the extra-copy genetic behavior back to its oldest evolutionary carrier: the sea sponge. It turned out the sponge had evolved the extra gene copy well before algae, sometime around -- you guessed it -- 640 million years ago.
"We brought together paleontological and genetic evidence to make a pretty strong case that this really is a molecular fossil of sponges," said Gold in a statement. "This is some of the oldest evidence for animal life."
"This brings up all these new questions," Gold added. "What did these organisms look like? What was the environment like? And why is there this big gap in the fossil record? This goes to show how much we still don't know about early animal life, how many discoveries there are left, and how useful, when done properly, these molecular fossils can be to help fill in those gaps."
Four new species of killer sponges, related to the non-synthetic sponges that might be in your kitchen or bathroom now, have just been discovered living deep in the Pacific Ocean, according to the Monterey Bay Aquarium Research Institute (MBARI). The sponges look more like ghostly plants than the blobby natural sponge you might use to do your dishes or in the bath. They consist of twig-like structures covered with microscopic hairs. The hairs, in turn, are packed with microscopic hooks that the hungry, flesh-eating sponges use to trap prey. Here's a close-up view of
MBARI marine biologist Lonny Lundsten and his team collected a few samples while exploring the deep sea floor from the Pacific Northwest to Baja California. After bringing them back to the lab, the researchers noticed many crustacean prey stuck within the sponges in various states of decomposition. The new sponges included:
- Monticolameans means "mountain-dweller" in Latin. This sponge was found atop the Davidson Seamount, which is an extinct underwater volcano.
- This spiny sponge was named after marine biologist Ed Ricketts, who was immortalized in John Steinbeck's book, "Cannery Row."
- The sponge was found hanging out on recent lava flows along the Juan de Fuca Ridge, a volcanic ridge offshore of Vancouver Island.
- It was discovered far to the south, in a newly discovered hydrothermal vent field on the Alarcon Rise, off the tip of Baja California. Here, a large group of
sponges are visible growing on top of a dead sponge at Davidson Seamount, offshore of the Central California coast.
Most sponges, even ones that might be in your home, are generally filter feeders that live off of bacteria and single-celled organisms sieved from the surrounding water. Lundsten explained that they contain specialized cells called choancytes, whose whip-like tails move continuously to create a flow of water that brings food to the sponge. Most carnivorous sponges, though, have no choancytes. As he said, "To keep beating the whip-like tails of the choancytes takes a lot of energy. And food is hard to come by in the deep sea. So these sponges trap larger, more nutrient-dense organisms, like crustaceans, using beautiful and intricate microscopic hooks." Here, a group of Asbestopluma monticola sponges grows on an ancient lava flow at Davidson Seamount, offshore of the Central California coast.
The deep sea can be inhospitable. Old lava flows, for example, aren't exactly stable surfaces. Hydrothermal vents, where
was located, can be incredibly hot. A group of Cladorhiza evae sponges are shown growing near a hydrothermal chimney along the Alarcon Rise, off the tip of Baja Calif.
Lundsten and his team hope to see the sponges hunt and eat their prey from start to finish, to better understand how that all works. It sounds like an undersea plot out of "Little Shop of Horrors!" These four new sponges could have a lot of ravenous relatives too. The manipulator arm on MBARI's remotely operated vehicle Doc Ricketts is seen here collecting a
sponge growing on a piece of carbonate crust on the seafloor off the coast of Southern California.