Paleontologists have discovered a fossil that radically changes the understanding of the origin of leeches. The finding shows that these creatures appeared at least 200 million years earlier than previously thought, and their earliest ancestors were likely not bloodsuckers.
A fossil approximately 430 million years old was found in the state of Wisconsin, USA. It has perfectly preserved the imprint of an ancient worm's body. It features a large tail sucker, similar to modern leeches, and a segmented, teardrop-shaped body. However, one important detail is missing — the front sucker, which modern leeches use to pierce the skin and drink blood. The study was published in the journal Paleontology and Evolutionary Science.
"This is the only body fossil we have ever found from representatives of this group," notes Karma Nanglu, a paleontologist from the University of California (USA).
The absence of a front sucker and the fact that the fossil was found in marine deposits indicate a completely different lifestyle for the first leeches. Scientists believe that they did not parasitize vertebrates but roamed the bottom of the ancient ocean, feeding on small invertebrates.
"Feeding on blood requires many specialized mechanisms — anticoagulants, a special mouth apparatus, specific enzymes. These are complex adaptations," explains Nanglu. "It is more logical to assume that early leeches swallowed their prey whole or perhaps drank the internal fluids of small soft-bodied marine animals."
The preservation of such a fragile organism is a great stroke of luck for science, as leeches have neither bones nor shells, which typically turn into fossils. Initially, the specimen was not identified. Karma Nanglu took on its identification during the pandemic, consulting with leech specialists. The decisive evidence was the tail sucker and clear body segmentation — characteristics specific to leeches. This finding is part of a larger effort to study the early stages of life development on Earth.
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