In a sample of 10 "P. boisei" specimens, brain size varied from with an average of . However, the lower-end specimen, Omo L338‐y6, is a juvenile, and many skull specimens have a highly damaged or missing frontal bone which can alter brain volume estimates. The brain volume of australopithecines generally ranged from , and for contemporary "Homo" . Regarding the dural venous sinuses, in 1983, American neuroanthropologist Dean Falk and anthropologist Glenn Conroy suggested that, unlike "A. africanus" or modern humans, all "Paranthropus" (and "A. afarensis") had expanded occipital and marginal (around the foramen magnum) sinuses, completely supplanting the transverse and sigmoid sinuses. In 1988, Falk and Tobias demonstrated that hominins can have both an occipital/marginal and transverse/sigmoid systems concurrently or on opposite halves of the skull, such as with the "P. boisei" specimen KNM-ER 23000. In 1983, French anthropologist Roger Saban stated that the parietal branch of the middle meningeal artery originated from the posterior branch in "P. boisei" and "P. robustus" instead of the anterior branch as in earlier hominins, and considered this a derived characteristic due to increased brain capacity. It has since been demonstrated that the parietal branch could originate from either the anterior or posterior branches, sometimes both in a single specimen on opposite sides of the skull as in KNM-ER 23000 and OH 5.