Some of the oldest dinosaurs didn't have hollow bones, suggesting that skeletal air sacs evolved independently in three lineages: long-necked sauropodomorphs, meat-eating theropods and pterosaurs.
Albert Einstein's theories of relativity have been proven to be true time and again in the more than 100 years following their publication.
A 2,000-year-old tomb discovered in Turkey was sprinkled with "dead nails" and sealed off with bricks and plaster, likely to "shield the living from the dead."
Sand is difficult to walk or run across. But why?