Complex sentence: Males also gouge trees with their toothcomb (a special arrangement of the bottom, front teeth) prior to chest scent-marking, resulting in their having brown-stained chests, the only visible trait that can be used to distinguish adult males from adult females.
Split into simpler sentences: Males also gouge trees with their toothcomb (a special arrangement of the bottom, front teeth) prior to chest scent-marking. This chest marking results in males having brown-stained chests, the only visible trait that can be used to distinguish adult males from adult females.