Some of the earliest animals on Earth may have emerged in the deep ocean, far from the shallow settings where most animal life thrives today.
A Dartmouth-led expedition to a remote site in Canada’s Mackenzie Mountains uncovered more than 100 new fossils, including six groups of organisms never before recorded in North America. The study, published in Science Advances, dates some of the specimens to about 567 million years old, 5 to 10 million years older than comparable fossils anywhere else.
The discovery also supports a striking hypothesis: that complex macroscopic life first emerged in deep, offshore waters and only later expanded toward the coast, the opposite of the pattern seen in most later animal evolution.
Associate Professor of Earth and Planetary Sciences Justin Strauss, a co-corresponding author of the new study, led the expedition that recovered the fossils. The remote site sits on the traditional lands of the Sahtú Dene and Métis, who provided the team with guidance and permission to access the area.
“The Mackenzie Mountains host some of the best exposures of these rocks in the world, but they are so remote that few researchers get the opportunity to work there,” says Strauss. He and his students and colleagues worked closely with collaborators from the Canadian and Yukon geological surveys for over a decade to share logistics and coordinate this research.
The fossils from this transitional chapter belong to what scientists call the Ediacaran biota: soft-bodied marine organisms that lived more than 500 million years ago and represent the first direct evidence of multicellular animal life. With shapes that range from flat discs to leafy fronds, Ediacaran species are linked to several modern animal groups, including mollusks, nematodes, comb jellies, and cnidarians (a group that spans jellyfish and corals). Others look nothing like anything alive today.
“For three billion years, life on Earth was dominated by microbes. Then, all the sudden, we get these strange-looking marine animals big enough to see and capable of behaviors we would find familiar today,” says study lead author Scott Evans, an assistant curator of invertebrate paleontology at the American Museum of Natural History.
The Dartmouth team at the Mackenzie Mountains site
Because most Ediacaran organisms lacked hard parts like shells or bones, their fossils are rare and require exceptional preservation conditions. Scientists have found them on every continent except Antarctica, but only a handful of sites offer a detailed window into this 40-million-year chapter of Earth’s history.
Researchers sort Ediacaran life into three “assemblages” tied to different points in the geologic record: the Avalon (575 to 559 million years ago), the White Sea (559 to 550 million years ago), and the Nama (550 to 538 million years ago). Until this study, White Sea fossils had been documented only in Russia, Namibia, South China, and Australia. Ediacaran fossils had been reported in the Mackenzie Mountains before, but this study marks roughly a five- to ten-fold increase in the number of taxa documented in the region.
“Not only is this new site highly diverse, but also it is from a part of the rock succession where we have previously lacked fossil remains,” Strauss says. “Given our understanding of the regional geology in northwestern Canada, there is great potential here to revise our understanding of Ediacaran Earth history.”
Several of the new finds offer particularly striking glimpses into early animal life. Among them is Dickinsonia, a flat creature with a divided circular body that the researchers describe as a “bathmat” or “pancake,” which drifted along the sea floor absorbing bacteria through its entire underside. There is also Funisia, a tube-shaped organism that lived in dense clusters and offers the oldest known evidence of sexual reproduction in the fossil record, likely through the coordinated release of sperm and eggs into the water column, similar to modern corals. Perhaps the most scientifically significant find is Kimberella, a sea-floor scraper with a muscular foot, widely interpreted as an early relative of mollusks and now potentially the oldest known motile bilaterian.
The fossils turned up in a setting scientists hadn’t expected for the White Sea assemblage: a deep-water continental slope environment. Until now, White Sea fossils had only been documented in shallow marine settings like continental shelves.
Deep water is generally dark and inhospitable, but it is also relatively stable, with fewer fluctuations in temperature and oxygen than coastal environments. That stability may have given early animal life the conditions it needed to take hold in a time period where Earth was undergoing dynamic climatic changes, such as the Neoproterozoic snowball Earth events.
The Mackenzie Mountains
The study was supported by a NASA Exobiology grant, on which Strauss is a co-investigator, and grants awarded to Strauss from the National Science Foundation. Other co-authors include Erik Sperling of Stanford University and Kimberly Lau of Pennsylvania State University. The fossils will eventually be permanently accessioned by the Prince of Wales Northern Heritage Centre in Yellowknife, Northwest Territories.
The rock layers where the team found these fossils are overlain by hundreds of feet of additional, potentially fossil-rich rock, stretching across a vast region of Yukon, the Northwest Territories, and British Columbia. Strauss plans to keep working there for years to come.
This summer, he’ll head to British Columbia to scout new sites, joined by Guarini PhD candidate London Warburton ’23 and undergraduates EllaMae Fitzgerald ’27, Willie Kellogg ’27, and Keegan Miller ’26.
“There is so much potential for exciting new discoveries in this part of the world, but it truly takes boots on the ground,” Strauss says. “Fortunately, I have a great crew of collaborators and Dartmouth colleagues and students who are keen to keep walking.”