Molecular clock
The earliest Lepidoptera fossils date to the Triassic-Jurassic boundary, around 200 million years ago. Butterflies evolved from moths, so while the butterflies are monophyletic (forming a single clade), the moths are not. The oldest known butterfly is "Protocoeliades kristenseni" from the Palaeocene aged Fur Formation of Denmark, approximately 55 million years old, which belongs to the family Hesperiidae (skippers). Molecular clock estimates suggest that butterflies originated sometime in the mid-Cretaceous, but only signficantly diversified during the Cenozoic. The oldest American butterfly is the Late Eocene "Prodryas persephone" from the Florissant Fossil Beds, approximately 34 million years old.