Final answer:
Ardipithecus ramidus is a hominin species that lived about 4.4 million years ago. It is believed to have been bipedal on the ground and quadrupedal in trees.
Step-by-step explanation:
Ardipithecus ramidus is a hominin species that was discovered in Ethiopia and is dated to about 4.4 million years ago. It is the first known hominin species to be dated to the Pliocene era. Based on its features, such as the forward position of the foramen magnum, small upper arm bones, and opposable big toe, it is believed that Ardipithecus was bipedal on the ground and quadrupedal in trees.