They had strange, branching forms, says Popular Science as they look over fossils from Newfoundland. And they took off centuries before the so-called “Cambrian explosion” when paleontologists used to think animal life suddenly became the complicated many-shaped menagerie of critters that eventually became crickets or cuckoos or coyotes. They evolved into wildly different forms, the theory went, because something terrible happened that made them change – like the asteroid that killed off the dinosaurs. But with this research, scientists are saying that “explosion” was more of a long, slow blaze that started with a bunch of hardly recognizable body shapes:
For around 3 billion years, single-celled organisms dominated Earth’s seas. The first animals emerged during the late Ediacaran, and some of the oldest organisms organisms dwelled in deep water and resembled plants with feathery-looking structures branching off a central stem. Others had segmented disk-like bodies.
“One of the really unique things about the oldest of these Ediacaran organisms is they have this strange fractal branching—they had branches of branches of branches,” [Cambridge paleontologist Emily] Mitchell says. “Studying Ediacaran organisms is really hard because their body plans are unlike anything else alive today or elsewhere in the fossil record.”
In an attempt to investigate how these animals lived and interacted with each other, Mitchell and her collaborators examined records of 86 Ediacaran fossil beds.
In the most ancient sites, the team identified few links between any particular species or habitats. But that changed with younger groups of fossils. Certain organisms tended to group at the same locations, while others never overlapped. Communities of Ediacaran organisms also varied more distinctly depending on the depth or geographic region they dwelled in.
“What that’s telling us is these species are adapting to each other and their environment,” Mitchell says.
This pattern—of increasing specialization over time—is the opposite of what’s expected after a cataclysmic event. When a massive volcano erupts or a dinosaur-killing asteroid strikes Earth, the species that survive or emerge afterward tend to be hardy generalists that can endure a broad range of conditions. That doesn’t fit the bill for the Ediacarans, Mitchell and her team observed.
“We see an increase in ecological complexity,” she says. “Even though we have a decrease in the [overall] number of species, that’s because they’re specializing, they’re finding their particular niches, rather than something external is killing them off.”
You can read more about Ediacaran lifestyles here, in PLOS Biology.