Final answer:
The statement is true; humans are the only mammals that engage in bipedal locomotion habitually. Other primates, such as apes, may walk on two legs at times, but they mainly use quadrupedal movement. 'Homo erectus,' an ancestor of modern humans, was already proficient in bipedal locomotion.
Step-by-step explanation:
The statement that today, humans are the only truly bipedal mammals is true. While other animals may exhibit bipedal traits, such as standing upright temporarily to reach food, humans are unique in their habitual use of bipedal locomotion. It is important to note that although all primates, including humans, are in the same biological order, not all primates are primarily quadrupedal. For instance, hominids like Homo erectus, which are in the same family as modern humans, were very efficient at bipedal movement similar to that of modern humans, with adaptations like a broader pelvis, longer legs, and arched feet that supported this mode of locomotion.
The discovery of Homo erectus fossils has revealed that this early human ancestor shared many features and adaptations with modern humans, making them an important part of our evolutionary history. Other primates, such as apes, may walk on two legs occasionally, but they are mainly quadrupedal and do not rely primarily on bipedal locomotion. The exceptional capability of humans to walk upright is one of the defining characteristics that sets us apart from other hominids and primates.