After 25 years of research, a 444-million-year-old inside-out fossil has finally been named. The fossil, which researchers at the University of Leicester have identified as a new species of multisegmented fossil, has been named Keurbos susanae, or “Sue” for short, after the lead researcher’s mom.

And while its insides seem to have been well-preserved, researchers are still debating what this organism may have been. The researchers published their findings in the journal Palaeontology. 

“‘Sue’ is an inside-out, legless, headless wonder. Remarkably, her insides are a mineralised time capsule: muscles, sinews, tendons, and even guts all preserved in unimaginable detail. And yet her durable carapace, legs, and head are missing – lost to decay over 440 million years ago,” Gabbott said in a press release. “We are now sure she was a primitive marine arthropod, but her precise evolutionary relationships remain frustratingly elusive.”

Unearthing the Fossil Keurbos susanae

Sarah Gabbott, the study’s lead author and a professor in the School of Geography, Geology, and the Environment at the University of Leicester, first uncovered K. susanae about 25 years ago, at the start of her career. The fossil was in the Soom Shale, which is about 250 miles north of Cape Town, South Africa. Though it may have taken years of painstaking research, Gabbott finally had some answers about this mysterious fossil. 

According to the study, arthropods make up about 85 percent of the animals on Earth and include lobsters, shrimp, centipedes, and spiders, among others. Arthropods have an extensive fossil record dating back about 500 million years. However, researchers typically find their exterior fossilized; in the case of K. susanae, it was the opposite. 

The area where Gabbott uncovered K. susanae was once the ocean floor some 440 million years ago. Within what would have been a marine basin, it appeared that K. susanae may have taken refuge from the Ordovician-Silurian extinction (the Late Ordovician mass extinction (LOME)), the first of the big five mass extinctions. 

During this time, global temperature dropped as ice sheets grew and altered oceans. By the end of it, about 85 percent of Earth’s species were eradicated. From the fossil, researchers can tell that after K. susanae died, it was buried by extremely toxic sediment. In place of oxygen, the ocean was full of hydrogen sulfide, which the researchers believe may have caused the organism to fossilize inside out. 

Read More: A New 450-Million-Year-Old Arthropod Was Preserved in Fool’s Gold

A Fossil That’s Difficult to Identify 

Though it is a fascinating feat that K. susanae has been fossilized inside out, the downside is that researchers aren’t sure what the exact species it is. Without the exterior, it’s difficult to compare this fossil to others in the fossil record from the same time period. 

On top of that, the quarry where Gabbott found the fossil is unlikely to yield any more specimens, though she hoped to one day find one that matched K. susane. Instead, she’s shifting focus. 

“This has been an ultramarathon of a research effort. In a large part because this fossil is just so beautifully preserved, there’s so much anatomy there that needs interpreting,” Gabbott said in a press release. “I’d always hoped to find new specimens, but it seems after 25 years of searching, this fossil is vanishingly rare — so I can hang on no longer. Especially as recently, my mum said to me, ‘Sarah, if you are going to name this fossil after me, you’d better get on and do it before I am in the ground and fossilized myself.’”

According to Gabbott, she would tell her mom she’d name a fossil after her because she’s a “well-preserved specimen.” But for Gabbott, the real reason was because her mom was the one who encouraged her to pursue a career she loved. In this case, it’s digging up fossils.

Read More: The 5 Mass Extinctions That Have Swept Our Planet

Article Sources

Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:

A graduate of UW-Whitewater, Monica Cull wrote for several organizations, including one that focused on bees and the natural world, before coming to Discover Magazine. Her current work also appears on her travel blog and Common State Magazine. Her love of science came from watching PBS shows as a kid with her mom and spending too much time binging Doctor Who.