Distinguishing between male and female human remains can be tricky, especially in cases where only partial skeletons are found. Ann Ross, a forensic anthropologist at North Carolina State University in Raleigh, and her colleagues have developed a new computer program called 3D ID that helps researchers make such distinctions based on skulls. Check out the video below, and as you watch the female and male skulls rotate, look for these features:

Nuchal crest: This area, where the muscles from the back of the neck attach to the base of the skull, is smooth and rounded in females but hooked and protruding in males.

Jaw: A female jaw is often smaller than a male's and either pointed or rounded, whereas a male's is broader and squarer.

Forehead: Female foreheads are more vertical than male foreheads, which gives the former a childlike appearance, Ross says.

Brow: An area called the supraorbital margin, which is just above the eye and roughly follows the brow line, is thin and pointy in females but more rounded in males. Male browridges are also more pronounced.

Even before a gender determination is made, researchers must figure out if remains belong to a human or a nonhuman animal. In fact, Ross keeps various partial animal skeletons and skulls on hand in her lab for reference and to help her train students to learn how to recognize differences among them.

» View a slide show and learn the identity of a few animal skulls