A bizarre fossilized creature from 444 million years ago has left scientists scratching their heads for over two decades. Discovered north of Cape Town in South Africa, this ancient arthropod stood out for a strange reason: it was preserved inside out.
Nicknamed “Sue” (officially Keurbos susanae), the newly identified species baffled paleontologists until Dr. Sarah Gabbott from the University of Leicester uncovered its secret — a discovery she details in a study published in the journal Paleontology.
“Sue’s innards are like a fossilized time capsule — muscles, tendons, even intestines preserved in astonishing detail. And yet, her tough outer shell, legs, and head are completely gone, lost to decay some 440 million years ago,” Gabbott explains.
The fossil was found in a low-oxygen (anoxic) marine environment — a crucial condition for fossilization. However, the surrounding water also contained hydrogen sulfide, which scientists believe may have dissolved the exoskeleton, as reported by Popular Mechanics.
Ironically, while Sue’s tough outer shell decomposed, her internal organs were preserved in extraordinary detail by calcium phosphate — the same mineral that makes up human bones and teeth. Gabbott is still working to unravel the exact chemical process that allowed this “inside-out” fossilization to occur.
A Place in the Tree of Life?
Paleontologist Sarah Gabbott at the site where she discovered the fossil
University of Leicester
The site where Sue was found was once the floor of a prehistoric sea, dating back to a time when a mass glaciation wiped out around 85% of all species on Earth. Although the fossil offers an unprecedented glimpse into the soft anatomy of an ancient marine arthropod, placing Sue within the evolutionary tree has proved challenging — even 25 years after Gabbott’s initial discovery.
“This has been a research ultramarathon. Because the fossil is so beautifully preserved, there’s a vast amount of anatomy to interpret — layers of intricate detail stacked on top of each other.”
Today, arthropods make up about 85% of all animal species on the planet, from shrimp and spiders to mites and centipedes. But Sue’s unusual anatomy and unique preservation continue to set her apart, offering scientists a rare and valuable puzzle piece in the story of life on Earth.
