Chapter 16, Problem 20A

Summary Introduction

To describe:

The relevance of the foramen magnum’s location to bipedalism.

Introduction:

The hominins include humans and all their extinct relatives. Hominins are bipedal. When they became bipedal, they developed a fully upright stance, shortened arms, restructured hip bones and foot bones and a change in position of head on spinal cord. These evolutionary changes led to bipedalism.

Answer to Problem 20A

In quadrupeds, the foramen magnum is located at the back of the skull while in hominins it is positioned at the base of the skull.

Explanation of Solution

Foramen magnum is the hole in the skull where the spine extends from the brain. In 1924, Raymond Dart discovered a skull of a young hominoid which had a braincase and facial structure similar to those of an ape. However, the skull had an unusual feature for an ape skull- the position of foramen magnum. In the fossil foramen magnum was located on the bottom of the skull as in humans and not in apes. The location of foramen magnum indicated that the organism walked upright. In apes and other quadrupeds the foramen magnum is located at the back of the skull as the spine is located more behind the head.

There are many advantages of bipedalism. When hominins evolved the landscape of Africa was changing and bipedalism was an adaptation to the new savanna environment. Food resources were sparse and far apart. The hominins had to travel long distances. By walking upright they could travel long distances more efficiently.