Final answer:
Homo erectus is distinguished from earlier and later hominins by their sagittal keel, prominent brow ridges, smaller jaws and teeth, and larger brain size. They were nearly as efficient at bipedalism as modern humans, with humanlike feet, and exhibited reduced sexual dimorphism compared to their predecessors. The use of fire and cooking led to smaller teeth with thicker enamel and a reduction in prognathism.
Step-by-step explanation:
The anatomical features that distinguish Homo erectus from earlier and later hominins include several key characteristics. Notably, Homo erectus possessed a sagittal keel, which is a small, raised ridge on top of the skull, a more pronounced brow ridge, and a projecting nasal spine. Unlike earlier hominins, such as australopithecines and some early Homo species, Homo erectus had a skull that was more human-like in shape with smaller jaws and teeth. Moreover, the brain size of Homo erectus was larger, ranging from 775 to 1,100 cubic centimeters, approaching the lower end of modern human brain size.
From the neck down, Homo erectus showcased bipedalism with a human gait and humanlike feet with arches and ankles, making them nearly as efficient at bipedal locomotion as modern humans. Their longer legs enabled them to run great distances, which suggests endurance running as a derived adaptation. Other adaptations related to a broader pelvis, which contributed to their efficiency in upright walking. Homo erectus also demonstrated reduced sexual dimorphism compared to earlier species, with males being only 20 to 30 percent larger than females.
Additional distinctions include smaller teeth with thicker enamel, which is attributed to the consumption of softer foods made possible through the use of fire and cooking. The reduction in prognathism (the extent to which the jaw protrudes) and the presence of longer, downward-facing nostrils also differentiated Homo erectus from their predecessors.