These bizarre fossils represent some of the earliest moving, sexually reproducing life ever discovered

Today a stretch of Canada’s remote Northwest Territories is covered in snowcapped peaks. But more than half a billion years ago this wilderness was a seafloor home to the wrinkled “pancakes,” fleshy fronds and spiral-shaped critters that were among Earth’s earliest complex life-forms.

Researchers recently unearthed a trove of fossils that reset the timeline for when these curious creatures scuttled onto the evolutionary scene. The new fossils, as described in Science Advances, also suggest that the deep sea served as an environmental cradle for complex life.

Found in Canada’s Mackenzie Mountains, the fossils date back 567 million years and provide a rare window into the geological period called the Ediacaran, which ended just before the Cambrian explosion of biological diversity. To reach the site, study lead author Scott Evans, a paleontologist at the American Museum of Natural History, and his colleagues embarked on a 14-hour drive and a helicopter flight.

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The fossils, many preserved as detailed imprints on slabs of mud-colored rock, were worth the journey. In total, the team collected more than 100 remnants of strange, soft-bodied creatures that are the first known to reach major milestones in the evolution of life as we know it. Compared with finds from earlier in the Ediacaran, these organisms “look a little more like animals that we’re familiar with,” Evans says. “They move around, and some of them are reproducing sexually.”

Among these early movers were the Frisbee-like Dickinsonia, which lacked a mouth and hoovered up algae through its underbelly, and Kimberella, a teardrop-shaped creature that scraped the seafloor and may be related to modern mollusks. The site also yielded fossils of spongelike, tubular organisms known as Funisia, which were among the first complex creatures to reproduce sexually. Scientists think they sent sperm and eggs into the water column like today’s corals do.

The fossils are among the earliest found for creatures of this complexity. This discovery “extends early animals deeper in time,” says Mary Droser, a paleontologist at the University of California, Riverside, who was not involved with the paper but discussed the fossils with the study authors. She notes that the animals of the Ediacaran have long been divided into distinct groupings, beginning with simple stationary species that were replaced by more complex creatures emerging around 559 million years ago. Instead the new fossils reveal that these groups lived side by side for millions of years.

The fossils’ location also provides crucial environmental context for the rise of ancestral animals. Based on the site’s rocks, which did not preserve ripples or other signs of waves, the team posits that this area was once part of the ocean floor.

As a result, the new site provides compelling fossil evidence that the earliest animals first emerged in deep-sea environments, says Lidya Tarhan, a paleontologist at Yale University, who was not involved in the new study. She says the fossils support previous hypotheses that proposed that early life gradually moved from the deep to the shallows, a trajectory that is “unusual in the evolutionary history of animals.”

Although the ocean’s perpetually cold and dark lower reaches may seem inhospitable, Evans notes that the deep sea has less variation in temperature and available oxygen than shallow environments. “That stability might have been a really great place for animals to first show up and evolve,” Evans says. “If you can figure out one temperature, you’re good to go.”