Current Issue March 2014 magazine cover  Save 81% off the
newsstand price!   Dinosaur Shocker   It turned out Bob had been
misnamed. “It’s a girl and she’s pregnant,” Schweitzer recalls
telling her lab technician when she looked at the fragments. On
the hollow inside surface of the femur, Schweitzer had found
scraps of bone that gave a surprising amount of information
about the dinosaur that made them. Bones may seem as steady as
stone, but they’re actually constantly in flux. Pregnant women
use calcium from their bones to build the skeleton of a
developing fetus. Before female birds start to lay eggs, they
form a calcium-rich structure called medullary bone on the
inside of their leg and other bones; they draw on it during the
breeding season to make eggshells. Schweitzer had studied birds,
so she knew about medullary bone, and that’s what she figured
she was seeing in that T. rex specimen.  Most paleontologists
now agree that birds are the dinosaurs’ closest living
relatives. In fact, they say that birds ar