 Triassic <unk> were often the dominant semiaquatic animals in their environments . Large assemblages of <unk> with hundreds of individuals preserved together have been found in the southwestern United States . They have often been interpreted as mass death events caused by droughts in floodplain environments . Recent studies show these dense assemblages were instead probably the result of currents accumulating dead individuals in certain areas . These environments seem to have had little diversity , as they were inhabited almost exclusively by <unk> . 
