Related Experiment Video
Updated: Jul 8, 2026
06:45
Automated Joint Space Detection Improves Bone Segmentation Accuracy
Published on: November 28, 2025
Metacarpal proportions in Australopithecus africanus.
1Hominid Paleobiology Doctoral Program, Department of Anthropology, The George Washington University 2110 G St. NW, Washington, DC 20052, USA. djgreen@gwu.edu
Journal of Human Evolution
|January 15, 2008
Summary
Australopithecus africanus hands show ape-like breadth but human-like length in their first metacarpals (MC1). This suggests dexterity but less thumb stress than later tool-making hominins.
Area of Science:
- Paleoanthropology
- Primate anatomy
- Evolutionary biology
Background:
- Australopithecus africanus exhibits derived cranial features but ape-like limb proportions compared to A. afarensis.
- Previous research indicates A. afarensis had ape-like hand proportions.
Purpose of the Study:
- To investigate if the hand proportions of Australopithecus africanus were also ape-like.
- Specifically, to determine if the first metacarpal (MC1) of A. africanus was short and narrow relative to other metacarpals.
Main Methods:
- Compared metacarpal shaft and articular proportions, focusing on MC1 breadth and length relative to other metacarpals (MC2-4).
- Utilized a resampling procedure to compare extant hominoids with the limited A. africanus fossil record (11 metacarpals).
- Validated the resampling technique by comparing resampled ratios with actual ratios from associated elements in extant samples.
Main Results:
- Australopithecus africanus metacarpals showed breadth ratios similar to great apes but significantly smaller than modern humans.
- Relative length of A. africanus metacarpals was significantly greater than chimpanzees and orangutans, and not significantly different from modern humans.
- MC1 breadth was more ape-like, while MC1 length was more human-like.
Conclusions:
- The hand proportions of Australopithecus africanus suggest a combination of ape-like breadth and human-like length in the first metacarpal.
- This unique configuration likely facilitated high manipulative dexterity.
- The slender, ape-like MC1 indicates A. africanus may not have subjected their thumbs to the same mechanical stresses as later stone-tool-producing hominins.
Related Concept Videos
01:15Bones of the Upper Limb: Ulna
The ulna and radius are parallel bones of the antebrachium or the forearm. The ulna lies medially and consists of a bony tip called the olecranon process at its proximal end. This hook-like projection articulates with the olecranon fossa of the humerus and forms the "hinged" ulnohumeral part of the elbow joint. This joint facilitates forearm extension and flexion while preventing its hyperextension. Similarly, the coronoid process, another bony projection on the proximal/anterior side of the...
01:09Bones of the Upper Limb: Radius
The radius is longer of the two bones that make up the human antebrachium or forearm. At the proximal end, the radius articulates with the capitulum of the humerus and the radial notch of the ulna to form the elbow joint. At the distal end, the radius articulates with the ulna via the ulnar notch, forming the distal radioulnar joint. Distally, the radius also attaches to the carpal wrist bones (scaphoid and lunate) to form the radiocarpal joint.
The radius has a nail-shaped head, and a short...
The radius has a nail-shaped head, and a short...
01:19Bones of the Upper Limb: Humerus
The upper limb consists of the arm, forearm, wrist, and hand bones. The humerus is the single bone of the upper arm region. Proximally, it has a large, spherical, smooth head that articulates with the glenoid cavity of the scapula to form the glenohumeral or shoulder joint. The margin of the head is the anatomical neck, a residual epiphyseal plate. Laterally it extends to form bony projections called the greater tubercle and the lesser tubercle. Next to the tubercles is the surgical neck, a...
01:09Changes in the Appendicular Skeleton with Age
The upper and lower limb initially develops as a small bulge called a limb bud, which appears on the lateral side of the early embryo. The upper limb bud appears near the end of the fourth week of development, with the lower limb bud appearing shortly after.
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying...
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying...
01:18Classification of Bones
The bones of the human skeletal system are of varied shapes, sizes, and functions. They can be classified based on their shape and function into four major classes: long bones, short bones, flat bones, and irregular bones. Some classifications include a fifth type, the sesamoid bones, as a separate class, whereas others categorize them under short bones.
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The long...
Long and Short Bones
The appendicular skeleton, particularly the upper and lower limbs, is primarily made of long and short bones. The long...
01:16Muscles of the Forearm that Move the Hand and Fingers
The muscles of the forearm that move the wrist, hand, and digits are numerous and diverse. They can be classified into two groups based on their location and function — the anterior and posterior compartment muscles.
Anterior Compartment
The anterior compartment muscles originate from the humerus. They primarily function as flexors and are also known as flexor muscles. They typically insert on the carpals, metacarpals, and phalanges. The superficial layer includes the flexor carpi radialis,...
Anterior Compartment
The anterior compartment muscles originate from the humerus. They primarily function as flexors and are also known as flexor muscles. They typically insert on the carpals, metacarpals, and phalanges. The superficial layer includes the flexor carpi radialis,...