The petaltails of the family Petaluridae are among the most ancient of the extant true dragonflies (infraorder Anisoptera), having fossil members from as early as the Jurassic, over 150 million years ago. A 2024 molecular phylogeny found that the petaltails comprise two clades, a Gondwanan clade and a Laurasian clade. Their divergence time was estimated at 160 million years ago. Modern petalurids include only 11 species, one of which, the Australian Petalura ingentissima, is by some measurements the largest of living dragonflies, having a wingspan of up to about 160 mm and a body length of about 125 mm (Tetracanthagyna plagiata of another family can match or exceed its wingspan). Another large Australian species is Petalura gigantea, commonly known as the giant dragonfly. In the United States, two species are found, Tanypteryx hageni in the west and Tachopteryx thoreyi in the east. The larvae live primarily in stream banks, mostly in burrows, but the larvae of the eastern US species, Tachopteryx thoreyi, the gray petaltail, live in depressions under wet leaves. The semiaquatic habitat of the larvae makes the petaltails unique in the modern dragonfly families.