open their mouth to any great extent. Likely the majority of them would employ a sit-and-wait strategy, similar to that of many modern amphibians. When suitable prey swam or walked within reach, the jaw would slam shut, the palatine tusks stabbing the hapless victim. The strain put on the teeth by this mode of feeding may have been the reason for the reinforcing labyrinthodont enamel typifying the group. Swallowing was done by tipping the head back, as seen in many modern amphibians and in crocodiles. Evolution of a deeper skull, better jaw control and a reduction of the palatine tusks is only seen in the more advanced reptile-like forms, possibly in connection with the evolution of more effective breathing, allowing for a more refined hunting style. Reproduction The labyrinthodonts had an amphibious reproduction — they laid eggs in water, where they would hatch to tadpoles. They would remain in water throughout the larval stage until metamorphosis. Only the metamorphosed individuals would eventually venture onto land on occasion. Fossil tadpoles from several species are known, as are neotenic adults with feathery external gills similar to those found in modern lissamphibian tadpoles and in the fry of lungfish and bichirs. The existence of a larval stage as the primitive condition in all groups of labyrinthodonts can be fairly safely assumed, in that tadpoles of Discosauriscus, a close relative of the amniotes, are known. Groups of labyrinthodonts The systematic placement of groups within Labyrinthodontia is notoriously fickle. Several groups are identified, but there is no consensus of their phylogenetic relationship. Many key groups were small with moderately ossified skeletons, and there is a gap in the fossil record in the early Carboniferous (the "Romer's gap") when most of the groups appear to have evolved. Further complicating the picture is the amphibian larval-adult life cycle, with physical changes throughout life complicating phylogenetic analysis. The Labyrinthodontia appear to be composed of several nested clades. The two best understood groups, the Ichthyostegalia and the reptile-like amphibians have from the outset been known to be paraphyletic. Tellingly, labyrinthodont systematics was the subject of the inaugural meeting of International Society for Phylogenetic Nomenclature. Ichthyostegalia The early labyrinthodonts are known from the Devonian and possibly extending into the Romer's Gap of the early Carboniferous. These labyrinthodonts are often grouped together as the order Ichthyostegalia, though the group is an evolutionary grade rather than a clade. Ichthyostegalians were predominantly aquatic