Complex sentence: In New Guinea, they are also common, existing within the coastal reaches of virtually every river system in the country, along with all estuaries and mangroves, where they overlap in range with the rarer, less aggressive New Guinea crocodile.
Split into simpler sentences: In New Guinea they are also common, existing within the coastal reaches of virtually every river system in the country, along with all estuaries and mangroves. There the overlap in range with the rarer, less aggressive New Guinea Crocodile.