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Miocene Ape: Proconsul
November 16, 2008Posted by on
Proconsul africanus is one of the very first primates that can be classified as an ape. It lived 25-15 million years ago in the forests of Eastern Africa, but had cousins spread all over the old world. Since it is such a basal hominoid, it shares certain features with both monkeys (catarrhines) and apes. Proconsul is monkey-like in its retention of thin tooth enamel, a narrow torso, and relatively short forelimbs related to its quadrupedal locomotor habits. With apes, it shares the lack of a tail, a larger brain relative to body size, and other features of the postcranium, discussed below.
Proconsul was a pronograde arboreal quadruped, meaning that when the animal walked, its body was parallel to the substrate instead of roughly perpendicular to it as in modern apes. Body size varied between the different species of the genus. While Proconsul was certainly capable of a variety of different postures, it shows no specializations to suspension. The ulnar styloid retained contact with the rest of the carpus, limiting adduction of the wrist. The lumbar spine was long compared to more modern apes, with 6-7 lumbar vertebra. The transverse process of the vertebrae arise from the vertebral bodies rather than the pedicle, which refelcts a large erector spinnae muscle. Erector spinnae is important in quadrupeds because it helps to solve the “suspension bridge problem” of quadrupeds: The quadrupedal body is supported by four columns at the distal ends, and a strong erector spinnae helps to keep the middle of the body supported. Erector spinnae is also important in quadrupedal locomotion because the ability to flex and extend the back will create a greater propulsive force. In some later apes, the erector spinnae has been greatly reduced as the result of a change in bauplan which moved the spinal column forward into the thorax in order to allow more flexibility at the shoulder. But Proconsul still retains the primitive condition.
The first rays in the hands and feet are well-developed in Proconsul, and phalanges are generally long. The thumb and big toe are especially long, reflecting the importance of grasping in Proconsul‘s locomotor repertoire. These adaptations combine to make an animal which practiced a careful, deliberate form of locomotion. Grasping became more important as a balancing mechanism, which meant that the function of the tail was lost. By distributing weight between several different supports, Proconsul was able to reach terminal branches of trees while still being capable of reaching a large body size. The generalized body form of Proconsul probably allowed many different adaptive radiations to take place, as shown by the diversity of the later Miocene apes.
Ward, Carol. (2007) Postcranial and Locomotor Adaptations of Hominoids.
Walker, A (1997) Proconsul: function and phylogeny. In: Function, phylogeny, and fossils: Miocene hominoid evolution and adapatations. Plenum Press, New York, pp 209-224.