Ostrich Present day To put their work in the broadest
possible context, Schweitzer's team worked with samples from a wide range
of animal types, fossil deposits, continents, and time periods. Shown here are blood vessels from the bones of an ostrich. The
ostrich was chosen because it's one of the most primitive of living
birds, which most paleontologists now agree are the dinosaurs' closest
living relatives. It is also big and must stand on two legs, so it has similar
biomechanical constraints as some dinosaurs. The dark red blobs filling
the vessels, which weave through white bone matrix, are blood breakdown
products.
