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Ancient Leech Fossil Redefines 200 Million Years of Evolution

10/2/2025

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Summary

Story summary

A 430-million-year-old leech fossil from Wisconsin's Waukesha biota, the only body fossil known from the Hirudinida group, pushes back the lineage by at least 200 million years.
The fossil lacks the forward sucker seen in modern leeches, suggesting ancient leeches did not feed on blood.
Instead, they likely consumed soft-bodied marine creatures or their internal fluids.
Preservation required low-oxygen conditions and immediate burial after death.
The study calls for reassessing assumptions about the evolutionary history of leeches.

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Story summary

A 430-million-year-old leech fossil from Wisconsin's Waukesha biota, the only body fossil known from the Hirudinida group, pushes back the lineage by at least 200 million years.
The fossil lacks the forward sucker seen in modern leeches, suggesting ancient leeches did not feed on blood.
Instead, they likely consumed soft-bodied marine creatures or their internal fluids.
Preservation required low-oxygen conditions and immediate burial after death.
The study calls for reassessing assumptions about the evolutionary history of leeches.