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The Adephaga is the second largest suborder of beetles, with over 40,000 known species. Most members are predacious (the Greek word "adephagos" means "gluttonous"). The two living families with terrestrial members, Carabidae and Trachypachidae, are occasionally called the Geadephaga; the remaining, aquatic families are the Hydradephaga. The majority of species in the suborder belong to the family Carabidae.
Adephagans diverged from their sister group in the late Permian, with the most recent common ancestor of living adephagans probably existing in the early Triassic, around 240 million years ago (Ponomarenko, 1977; Erwin, 1979). Both aquatic and terrestrial representatives of the suborder appear in the fossil record in the late Triassic, with a Jurassic fauna consisting of trachypachid, carabid, gyrinid, and haliplid-like forms (Ponomarenko, 1977). The familial and tribal diversification of the group spans the Mesozoic period, with a few tribes radiating explosively in the Tertiary (e.g., members of the carabid subfamily Harpalinae, Erwin, 1985).
Adephagans are diverse in diet and structure. Most are general predators, although algal feeders (Haliplidae), seed feeders (many harpaline carabids), fungal feeders (rhysodines), specialist predators on snails (licinine and cychrine carabids), and ectoparasitoids of other insects (brachinine and lebiine carabids) or millipedes (peleciine carabids), occur. Many lineages have gone down, into caves, while others have gone up, into the rain forest canopy or alpine habitats. The body forms of some have become highly modified structurally for life in unusual habitats (e.g., gyrinids at the air-water interface, paussine carabids in ants' nests, rhysodines in heartwood). Some are ovoviparous (pseudomorphine carabids, Liebherr and Kavanaugh, 1985). A variety of chemical defense mechanisms have evolved in the group, including the explosive discharge of bombardier beetles (Aneschansley et al., 1969).