SAT Text Structure and Purpose Question

Postcranial skeletal pneumaticity(PSP)refers to the presence of extensions of an animal's lungs and air sacs inside its bones. These extensions are known as pneumatic diverticula. Vascularity and other identifying characteristics of pneumatic diverticula tend not to fossilize, so paleontologists have relied on studies of living bird species to document these qualities, augmenting their findings from fossil analysis to glean additional insights into the respiratory systems of extinct genera such as Tyrannosaurus, Euhelopus, and other Cretaceous theropods and sauropods that may have also exhibited PSP. Which choice best describes the function of the underlined portion in the text as a whole?