The discovery of what is believed to be fossilized, 1.6-billion-year-old red algae suggests that advanced multicellular organisms evolved far earlier than previously believed, according to the authors of a new study published online Tuesday in the journal PLOS Biology.
While working near the town of Chitrakoot in central India, Stefan Bengtson, professor emeritus of paleozoology at the Swedish Museum of Natural History, and his colleagues discovered a pair of red algae-like fossils that had been unusually well preserved in sedimentary rocks.
One of the fossils was described as thread-like, while the other was said to be made up of fleshy colonies. In both cases, the researchers said that they spotted the distinct inner-cell structures and bundles of packed filaments known as cell fountains that are typically found in red algae.
“You cannot be 100% sure about material this ancient, as there is no DNA remaining,” Bengtson said in a statement, “but the characters agree quite well with the morphology and structure of red algae,” which would make them significantly older than the 1.2-billion-year-old fossils which are currently believed to be the oldest known specimens of red algae in the world.
In fact, if their fungal status is verified, the newfound red algae would predate the oldest known plant-like fossils by approximately 400 million years. That, Bengtson noted, would indicate that “the ‘time of visible life’ seems to have begun much earlier than we thought.”
Discovery may push back the origins of multicellular life
The earliest known signs of life on Earth have been dated back to at least 3.5 billion years old, but as the researchers pointed out, these organisms were single-celled eukaryotes which lacked nuclei and other organelles. Large, multicellular organisms first emerged 600 million years ago, around the beginning of the “time of visible life” (better known as the Phanerozoic Era).
At least, that’s what scientists have long believed. Now, the discovery of this purported red algae could prove that this shift occurred far earlier than previously believed. The fossils were found in stromatolites, or fossilized mats of cyanobacteria, in 1.6 billion-year-old Indian phosphorite.
Bengston’s team discovered the thread-like forms of the red algae first, and as they were in the process of investigating it, they found the more complex, fleshy colonies. They analyzed the red algae using synchrotron-based X-ray tomographic microscopy, and discovered evidence that the fossils were indeed “probable crown-group rhodophytes (red algae).”
“The most conspicuous internal objects in the cells of the filamentous forms are rhomboidal platelets that we interpret to be part of the photosynthetic machinery of red algae. The lobate forms grew as radiating globular or finger-like protrusions from a common centre,” the study authors wrote. “These fossils predate the previously earliest accepted red algae by about 400 million years, suggesting that eukaryotes may have a longer history than commonly assumed.”
Image credit: Stefan Bengtson