British zoo critters weigh-in Pictures British zoo critters weigh-in A 40-gram Waxy Monkey Frog is weighed at the London Zoo, Aug. 21, 2013 in London, England. The height and mass of every animal in the zoo, of which there are over 16,000, needs to be recorded. The measurements are collated in the Zoological Information Management System, from which zoologists can use the data to compare information on thousands of endangered species. Credit: Bethany Clarke/Getty Images