He said that his team and the laboratories they employed took special care to avoid contamination.
Schweitzer answered the challenge by testing with antibodies.
Her report in 2009 confirmed the presence of collagen and other proteins that bacteria do not make.
In 2011, a Swedish team found soft tissue and biomolecules in the bones of another creature from the time of the dinosaurs, a Mosasaur, which was a giant lizard that swam in shallow ocean waters.
Researchers have found a reason for the puzzling survival of soft tissue and collagen in dinosaur bones - the bones are younger than anyone ever guessed.
Carbon-14 (C-14) dating of multiple samples of bone from 8 dinosaurs found in Texas, Alaska, Colorado, and Montana revealed that they are only 22,000 to 39,000 years old.