It's a question visitors ask staff all the time at the Smithsonian's National Zoo's Bird House. The answer may surprise you!

Evidence of avian beginnings has been elusive in the fossil record because birds' light, hollow bones rapidly decompose ... This odd, crow-sized creature had long legs and three toes tipped ...

To determine this rate of decline, an international team of paleogenetisicts examined DNA samples from 158 leg bones belonging to three species of Moa, extinct giant birds from New Zealand. The bones ...