The 510-million-year-old fossils from the Forteau Formation of Newfoundland and Labrador, Canada, are microscopic, look like spiny balls connected together, and likely represent vegetative stages of planktic green algae.
Coenobial microfossils from the Forteau Formation, including: (a, f) strut-form colonies, (b-e, h-k, m-o, s-u) plate-form colonies, and (g, l, p-r) ring-form colonies. Scale bar – 20 µm. Image credit: Thomas H.P. Harvey, doi: 10.1098/rspb.2023.1882.
“When I first saw them, I had no idea what they were,” said University of Leicester paleontologist Tom Harvey, author of a paper published in the journal Proceedings of the Royal Society B.
“I wondered if they could be animal eggs, or some new type of organism. There’s nothing quite like them, living or extinct.”
But as further specimens came to light, Dr. Harvey identified similarities with modern green algae that live floating in the plankton of ponds and lakes.
“The fossils have the same sort of colonial structure as the modern algae, with cells linking together, explaining their neat, geometric arrangements,” he said.
“Surprisingly, though, the fossil examples lived in the sea, giving a rare glimpse of the early marine plankton.”
The microfossils are approximately 510 million years old (Cambrian period).
They were found in the Forteau Formation of Newfoundland and Labrador in Canada.
“The importance of the fossils lies in their immense age,” Dr. Harvey said.
“They lived around the time when animals were first evolving, during the Cambrian explosion — and this is probably no coincidence.”
“In today’s world, phytoplankton provides the fundamental food source for almost all life in the oceans.”
“However, the modern groups of phytoplankton evolved relatively recently, and we do not know which groups inhabited the Cambrian oceans.”
“When we look at modern plankton, we see that algae develop colonies when animals are trying to eat them. It’s a defence mechanism. So, the existence of colonial algae in the Cambrian period suggests that early animals were evolving to feed in the plankton, starting a predator-prey relationship that has continued ever since.”
“Considering that the plankton underpins life in the oceans, and fossil plankton helps us build ancient climate models, these small fossils have a big role in telling the history of life on Earth.”
The discovery will prompt a re-think on other early microfossils. For years, paleontologists have thought that the spiny balls found individually were the dormant cysts of single-celled life. For Dr. Harvey, the new fossils seriously challenge this view.
“I wonder if we’ve been getting it all wrong, and in fact lots of these microfossils were living as colonies in the plankton,” he said.
“It’s easy to accidentally break up the fossils as we extract them from the rocks, so we all need to get back to the collections, back to our labs, and find out how common they really were.”
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Thomas H.P. Harvey. 2023. Colonial green algae in the Cambrian plankton. Proc. R. Soc. B 290 (2009): 20231882; doi: 10.1098/rspb.2023.1882
