Final answer:
The pronounced brow ridges, projecting nasal spine, thick skull bones, and the sagittal keel are signature characteristics of Homo erectus skulls.
Step-by-step explanation:
A signature characteristic of Homo erectus skulls are the pronounced brow ridges, along with a projecting nasal spine and thick skull bones. The pronounced brow ridges, projecting nasal spine, thick skull bones, and the sagittal keel are signature characteristics of Homo erectus skulls. These features are quite distinctive when compared to other hominids such as Homo habilis and Homo ergaster. The sagittal keel, a small raised ridge on top of the skull, is also a notable feature of Homo erectus skulls. These characteristics helped Homo erectus to survive in diverse environmental conditions and likely contributed to their relative longevity as a species.