In biology, describing a tail fin that is asymmetrical with the vertebral column extending into one lobe more than the other.
From Greek hetero- (different) plus kerkos (tail) plus -al (adjective suffix). A technical term in ichthyology (fish science) describing tail morphology.
Heterocercal tails are an evolutionary 'first draft'—sharks have them, and ancient fish fossils show them, but modern fish mostly 'edited' this design to make tails more symmetrical and efficient for swimming!
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