Carcharhiniformes

Carcharhiniformes (; from Ancient Greek καρχαρός (karkharós) 'sharp, jagged', ῥινός (rhinós) 'nose' and Latin forme 'shape'), commonly called ground sharks, are the largest order of sharks, with over 270 species. They include a number of common types, such as cat sharks, swellsharks, and hound sharks. Members of this order are characterized by the presence of a nictitating membrane over the eye, two dorsal fins, an anal fin, and five gill slits. The families in the order Carcharhiniformes are expected to be revised; recent DNA studies show that some of the conventional groups are not monophyletic. The oldest members of the order appeared during the Middle-Late Jurassic, which have teeth and body forms that are morphologically similar to living catsharks. Carchariniformes first underwent major diversification during the Late Cretaceous, initially as mostly small-sized forms, before radiating into medium and large body sizes during the Cenozoic.