Ancient fossil from China reveals animal-microbe partnerships dating back 550 million years

The Conotubus fossil is a small tube-shaped organism that lived around 550 million years ago. Most likely it was a soft-bodied animal resembling a worm. (Author), CC BY Ancient fossil from China reveals animal‑microbe partnerships dating back 550 million years Published: September 2, 2026 11.45am EDT Share article Print article We often think of microbes as organisms that live around us, like the salmonella bacteria and flu viruses that cause illness. But some of our most intimate relationships are actually with the microbes living inside of us. Incredibly, about half of the cells in the human body are actually microbial inhabitants. Scientific attention to the microbiome has helped us understand how many of them support our health; for example, by helping us digest food or by supporting our immune system. Elsewhere in the animal kingdom, microbes forge even more remarkable partnerships with their hosts. They help generate energy for coral and deep sea tube worms, and break down stubborn molecules like cellulose and lignin within animals as varied as cows and termites. They even help squid camouflage themselves. But how long have such partnerships existed? New research led by Zhenfei Wang and Yongbo Peng from Nanjing University, on which I was a co-author, has now found evidence of these close relationships between animals and microbes in a 550 million-year-old fossil from southern China. Prior to this, the earliest evidence of symbiosis was documented in fossils 100 million years younger. The Hawaiian bobtail squid uses the light produced by its luminous bacterial symbiont, Vibrio fischeri, as a camouflage. (Wikimedia), CC BY An ancient tube-shaped fossil Tracing animal-microbe symbiotic relationships back hundreds of millions of years is extremely challenging. The fossil record is altered, incomplete and biased toward organisms and environments that preserve well. Even exceptionally preserved fossils rarely retain evidence of the microbes that once lived within an animal. This fact makes ancient symbiotic relationships very difficult to identify. Given these challenges, our international research team sought to explore geochemical fingerprints of past microbe-animal interactions. We specifically focused on the tubular fossil conotubus that lived during the Ediacaran period, which extends from approximately 635 million to 541 million years ago. Occurrences of Ediacaran-aged fossils like the conotubus are rare. Extremes temperatures on…