Final answer:
Australopithecus afarensis, living from 3.9 to 2.9 MYA, demonstrates evolutionary trends such as reduced dentition and jaws and features indicative of both tree-dwelling and bipedal movement, with a cranial capacity similar to modern chimpanzees.
Step-by-step explanation:
Temporal Trends in Australopithecus afarensis: The species Australopithecus afarensis is significant in the study of human evolution, with temporal trends including the reduction in the size of dentition and jaws compared to earlier primates. Dated from 3.9 to 2.9 million years ago (MYA), A. afarensis exhibited both arboreal and bipedal locomotion characteristics. Key features of this species include long arms and curved fingers and toes, suggesting tree-dwelling behavior, combined with a pelvic structure more similar to modern humans, indicating the advent of bipedalism. The fossil known as "Lucy" (KNM-AL-288) provides substantial insights into this species' morphology. In terms of cranial capacity, A. afarensis had an endocranial volume similar to a common chimpanzee, around 380 to 450 cubic centimeters. With a trend towards smaller canines and molars than apes but larger than modern humans, A. afarensis represents an important formative stage in the evolutionary path to Homo sapiens.