Half a billion years ago, the waters were populated by mysterious organisms that looked very weird and about which we know precious little. We don’t know if most were animal or plant, or sessile or motile, though the thinking is that most stuck to the seafloor. As far as we know, all went extinct, making it impossible for today’s scientists to extrapolate about their lifestyle from extant descendants.
It helps to study a long-gone fish by looking at latter-day fish. But what can you say about Ediacarans, which look like they were created by a sci-fi cartoonist on drugs?
Inquiring minds equipped with very small fossils and advanced technology have figured out that an Ediacaran called Ernietta lived gregariously, feeding through family-style meals, as reported in Science Advances (“Gregarious suspension feeding in a modular Ediacaran organism”).
How long multicellular animals have existed is not clear. Some argue they existed — and were actively burrowing for food, no less — 2.1 billion years ago. Others think evidence is weak. But clearly the Ediacarans that lived between 570 to 540 million years ago, give or take, preceded the complex forms of life that would evolve into today’s animals.
Gregarious feeding in Ernietta would be one of the oldest examples ever found of commensalism, an arrangement in which one species benefits hugely and one is, at worst, not harmed.
Tick birds on rhinos are a great example: The birds rid the rhinos of arthropod infestation, and gain nutrition. The rhinos aren’t about to flop over from anemia because of ticks, but it’s nice for them.
Ernietta was found in Namibia, then a shallow sea. Finding the little critters was one minor miracle — and now elucidating how they ate is another.
Based on fossil scratches, one Ediacaran, Kimberella, is thought to have grazed bacteria off the seabed surface. Other Ediacarans are largely not thought to photosynthesize: at least some of them lived too deep for sunlight to reach. Nor did they subsist on absorbing chemicals (chemoautotrophy) as a group, because they didn’t necessarily live by methane vents. There were definitely no sign of any such vents in fossil Namibia.
As for wee Ernietta, Brandt Gibson of Vanderbilt University and colleagues achieved their feeding model by combining fossil data with computational fluid dynamics — computer simulations of fluid flow. The team tested the two basic competing models of Ediacaran eating in general: passive osmosis (absorbing organic chemicals from the water) and “suspension feeding” — trapping microbes or particles suspended in the seawater.
The model that best suited the fossil evidence is that Ernietta was trapping suspended foodstuffs.
The surprise was that the more Erniettas, the merrier: The primordial beasts fossilized en famille. Communities were found together. The model found enhanced water mixing around groups of Erniettas (almost as if they were paddling) and preferential redirection of the water current into the body cavities of downstream individuals. The family that eats together gets more food individually, apparently.
“They were enhancing the amount of nutrients going from individual to individual, and they were also exporting waste down-current and away from the one making it,” explained Gibson in Vanderbilt News. “So it was a good dinner party in that they got to eat a lot and didn’t have to sit in their own waste,” added project paleontologist Simon Darroch.
Ergo, the Erniettas seem to have enjoyed a gregarious ecology, as many of today’s marine invertebrates do. These were very, very early family meals.
So don’t let the kids get away with blowing off family meals. They go back a long way.