 Body impressions of Early <unk> <unk> from Pennsylvania suggest that some terrestrial <unk> mated on land like some modern amphibians . They reproduced through internal fertilization rather than mating in water . The presence of three individuals in one block of sandstone shows that the <unk> were gregarious . The head of one individual rests under the tail of another in what may be a courtship display . Internal fertilization and similar courtship behavior are seen in modern <unk> . 
