Mary Anning, "the greatest fossilist the world ever knew," got her start at the age of 12 when she and her brother Joseph discovered "what she would later find to be a remarkably complete Jurassic-era fossil of an Ichthyosaurus, a prehistoric marine reptile."
From Atlas Obscura:
Over the years that followed, Anning made further discoveries of fossils that revolutionized science. However, in spite of her phenomenal contributions, Anning was rarely recognized officially for her discoveries, which were instead credited to the wealthy “gentlemen scientists” who bought the fossils. She was also consistently refused entry to the Geological Society because she was a woman.