They usually fit in the palm of your hand, but some salamanders grow to human-sized proportions. Dr. Brady Barr goes in search of the "big four" of giant salamanders.
The world's largest freshwater fish are losing the fight for survival as pollution, overfishing, and construction threaten the rivers and lakes they call home.
Roughly 38 percent of the world's known species are near extinction, according to a comprehensive survey done to create the 2008 Red List of Threatened Species.