25-Year Study of Rare 444-Million-Year-Old Fossil Concludes with New Insights

The fossil 'Sue,' preserved in an 'inside-out' state, offers a glimpse into ancient marine life during a mass extinction but leaves evolutionary questions unanswered.

• The fossil 'Sue,' officially named Keurbos susanae, dates back 444 million years and was discovered in South Africa's Soom Shale formation.
• Sue's soft tissues, including muscles, tendons, and guts, were preserved in exceptional detail due to a toxic, oxygen-deprived environment.
• The fossil's unique 'inside-out' preservation lacks external features like a carapace, head, or legs, complicating efforts to determine its evolutionary lineage.
• The findings connect Sue to the Ordovician-Silurian extinction event, which wiped out nearly 85% of species, but the marine basin where it lived served as a refuge.
• The quarry where Sue was unearthed is now mostly depleted, making further discoveries of similar specimens highly unlikely.

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