Sixgill Sharks Have Six Gill Slits — A Primitive Trait From 200 Million Years Ago

This giant predator still carries an ancient feature most sharks lost.

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The order Hexanchiformes includes some of the most ancient living shark lineages.

Most modern sharks have five gill slits, but sixgill sharks possess six, a trait linked to ancient shark lineages that date back more than 200 million years. Their anatomy represents a living connection to early Mesozoic shark evolution.

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The extra gill slit is not cosmetic; it reflects deep evolutionary divergence from most modern shark families. Sixgills belong to the Hexanchiformes, a primitive order that retained features lost by faster, more derived sharks.

Encountering a sixgill is effectively encountering a body plan that predates the dinosaurs’ extinction. In the deep ocean, evolutionary time moves differently, preserving anatomical designs that survived planetary catastrophes.

Source

Smithsonian Ocean Portal

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