The evolution of stingrays (Myliobatiformes) is assessed using a new phylogeny with near-complete genus-level sampling, and additional molecular data. Stingrays diversified into three primary clades: (A) river stingrays, round rays and typical stingrays, (B) butterfly rays and stingarees and (C) eagle and manta rays. The enigmatic sixgill and deepwater rays (Hexatrygon and Plesiobatis) are not basal stingrays, but are part of the second clade. There is extensive clade-specific variation in molecular evolutionary rates across chondrichthyans: the most appropriate (autocorrelated) divergence dating methods indicate that the extant stingray radiation commenced in the late Cretaceous and continued across the K-Pg boundary. This is highly consistent with the fossil record, and suggests that Cretaceous stingrays, being primarily benthic taxa, were less affected by the K-Pg event than taxa inhabiting the water column. The largest pelagic radiation of stingrays (myliobatids: eagle and manta rays) evolved very shortly after the K-Pg boundary, consistent with rapid ecological expansion into newly-vacated pelagic niches.