I do not pretend to know anything about sagittal crests, but I found this which seems to be a reasonable explanation.
A sagittal crest is a bony ridge running lengthwise across the middle of the top of the skull from front to back. The sagittal crest indicates the presence of strong jaw muscles as the muscles that enable chewing are anchored to the sagittal crest. It can then be said that the larger the crest, the more powerful the jaws. Paranthropus in some cases had massive sagittal crests to go along with massive molar teeth. This allowed them to chew the toughest of foods. Female Paranthropus also had sagittal crests. Having a sagittal crest would cause the head to look pointed or conical. As such Paranthropus species would have had a conical shape to the top of their head.... Homo erectus, on the other hand, did not have a sagittal crest with the exception of a few Asian fossils. Rather than having a sagittal crest Homo erectus had a sagittal keel. A sagittal keel is a thickening of the bone that runs lengthwise across the top of the skull in a similar position as the sagittal crest. A sagittal keel would not produce a conical shape to the top of the head as they did not protrude far enough to form a noticeable feature.http://www.cryptozoology.com/blog/blog.php?id=1842
Most Homo sapiens lost them likely as part of the general trend toward thinning of the cranial bones during the Pleistocene, to make room for larger brains. However there is a very small portion of modern humans who have this, but we do not know why they do. Patrick Stewart of Star Trek is a good example of a modern human (Homo sapiens sapiens) that has this feature.
I would also point out that gorillas and humans do not share a common ancestor, whereas chimpanzees, whom also do not have a saggital crest, do share a common ancestor with humans.
· 9 years ago