Note: These materials are intended as supplements for students in Ant. 301. These pages are in development and will contain errors.
Primate Anatomy

 

 


   Deciduous  Permanent
 Maxilla

 2 1 2

 2 1 2 3
 Mandible

 2 1 2

 2 1 2 3


Endocranial Volume (in cm3)
[From Aiello and Dean 1990, Pp. 193]

 Species  Lower 95% Limits for Mean  Upper 95% Limits for Mean

 Mean

 Human

  1,159

 1,243

 1,201

 Chimpanzee

 391

 409

 400

 Gorilla

 452

 486

 469

 Orang

 385

 409

 397

The larger human brain volume also means that the calvarium is large relative to the size of the face. As the brain expands (comparing chimp and human), it appear to flex on an axis around the pituitary fossa. This produces flexion of the cranial base, a downwards shift in the posterior part of the cranium, and a forward rotation of the foramen magnum.

Expansion of the occipital lobes and cerebellum balloons the posterior cranial fossa, that in turn correlates typically with an asymmetrical cranial venous sinus system. In the human, a superior sagittal sinus drains venous blood in a transverse sigmoid route to the internal jugular veins. Enlarged occipitomarginal sinus systems typical of humans are infrequent in chimpanzees. The human middle cranial fossa expands with enlarged temporal lobes of the brain expanding the mid-section of the calvarium outward above the petrous portion of the temporal bone and the glenoid fossa. In chimpanzees, the calvarium is narrower than the cranial base but the human calvaria has its maximum width high on the parietal eminences rather than low at the cranial base. The anterior cranial fossa expands with the human frontal lobes. Consequently humans lack the postorbital constriction that occurs in chimpanzees and humans exhibit frontal eminence (forehead) above a greatly less obvious supraorbital torus (eyebrow ridge). Olfactory nerve tracts pass through the cribriform plate, a sieve-like structure in the middle of the ethmoid bone. In humans the median plane of the cribriform plate is the site of a process, the crista galli. This process is diminutive or absent in chimpanzees.

Ballooning of the calvaria in the temporal and occipital areas associated with the expansion of brain volume produces an apparent forward shift in the relative position of the foramen magnum. The human foramen magnum lies on a line, the bitympanic line, that connects the most inferior points on the lateral end of the right and left tympanic plates. The chimpanzee foramen magnum lies well behind the bitympanic line.

(2) nuchal crests -- Muscles that attach to the cranial base serve to position, move, and stabilize the head and cervical vertebrae. From a functional perspective, the skull is also the most superior point of origin for muscles (such as M. trapezius) that provide movement and stability to the back and shoulder. Consequently, some of the powerful muscles that attach to the skull have large attachment surfaces. The human occipital is a cup-like bone with a noticeable eminence, the external occipital protuberance. It is marked by nuchal lines and markings that represent attachment surfaces. The nuchal crests of the chimpanzee are more extreme. Its small skull combined with a much more robust musculature produces strong crests. Due to the flexion of the cranial base with expanded endocranial volume, the superior nuchal line is lower on the human skull.

(3) mastoid process -- The human mastoid process, the attachment surface of the sternocleidomastoid muscles, is distinct and separated from the outline of the occiput by a digastric fossa.

(4) premaxilla -- The smaller human incisivum, a homologue of the chimpanzee premaxilla, unites with the maxilla near the time of birth. The chimpanzee premaxilla is expanded to support the large and forward projecting incisors. It unites with the maxilla postnatally and the suture between it and the maxilla becomes obliterated.

(5) facial prognathism -- The projection of the face beyond the calvaria is greater in chimpanzees than humans. Flat faces are called orthognathic and projecting faces are called prognathic. The craniofacial angle, the angle between the most anterior point on the maxilla, the most anterior point of the sphenoid bone and the most anterior point of the foramen magnum, is used to quantify the extent to which the face projects beyond the neurocranium. Since this angle can not readily be measured on intact skulls, the angle that a sellion-prosthion line makes with the Frankfort plane serves as a convenient measure of facial projection. [The "Frankfurt plane" is the plane that passes through porion (right and left) and orbitale (right and left).] The porion is the most lateral and superior point of the external auditory meatus. The orbitale is the lowest point on the infraorbital margin. The sellion is the deepest point in the hollow beneath the glabella in the median plane. The glabella is the most anterior point in the median plane on the supraorbital torus. The prosthion is the most anterior point on the maxilla in the median plane.]

(6) chin -- The human mandible is reinforced by a bar of bone, the mental protuberance, that strengthens the symphysis, the union of right and left halves of the bone. The lingual or posterior surface of the symphysis bears a pair of genial tubercles that represent muscle attachment sites for M. genioglossus and M. geniohyoid. The ape mandible lacks a mental protuberance and is reinforced by an inferior transverse torus or "simian shelf". Viewed from above, the contrasting shape of the dental arcades is distinct.

(7) hyoid -- The human hyoid is a U-shaped bone just above the larynx. The stylohyoid ligament attaches the lesser horn of the hyoid to the styloid process of the temporal bone. Generally, these styloid processes point to the lesser horns of the hyoid bone. The chimpanzee hyoid is expanded anteriorly to accommodate a laryngeal air sack, and is located higher in the neck (return to outline).

The human vertebral column consists of 33 vertebrae divided into five functional regions.

1. Seven cervical vertebrae, easily recognized by their transverse foramina, form the skeleton of our neck. The joints (articular surfaces) between cervical vertebrae are very mobile.

2. Twelve thoracic vertebrae, mobile only in the coronal plane, support the ribs.

3. Five robust lumbar vertebrae in the lower back are tightly articulated to withstand the weight of the torso.

4. Five sacral vertebrae fuse to form the sacrum, the component of the axial skeleton in the pelvis.

5. Four caudal vertebrae extend downward from the sacrum. In adults these caudal vertebrae unit to form the coccyx, a hidden human tail that partially blocks the inferior pelvic aperture.

Viewed from the side, humans have a series of four curvatures. The dorsal outline of the cervical and lumbar regions are concave while the thoracic and sacral regions are convex. The forward curve of the lumbar region is called lordosis and that of the thoracic region is called kyphosis.

Chimpanzees generally to have one more thoracic, one less lumbar vertebra, and one less caudal vertebra than do humans. Both normally have seven cervical vertebrae and normally the combined thoracic, lumbar, and sacral regions consists of 22 vertebrae. Chimpanzees lack the extreme curves of the human column, and the angle between the lumbar and sacral region is more acute .


(return to outline)

Thorax

The human chest consists of 12 paired ribs that articulate with the vertebral column. Ribs I through VII attach ventrally to the sternum. Ribs VIII through X terminate in cartilage extensions that eventually fasten to the sternum. Ribs XI and XII have free distal ends. The sternum is composed of six flat bones that fuse in adults to three units, the manubrium (segment I), body (segments II through V), and xiphoid process (segment VI). In some persons, especially in old age, the three units of the sternum may fuse to each other.

Consistent with their extra thoracic vertebra, chimpanzees usually have one extra rib (13 pairs). The human rib cage is slightly broader for its depth than the chimpanzee and the human thorax is less funnel-shaped. Chimpanzee ribs are also somewhat rounder in cross-section than human ribs (return to outline).

Pectoral Girdle

The shoulder is formed by the humerus, clavicle and scapula. The clavicle attaches firmly to the manubrium and acts as a strut to hold the shoulder joint away from the chest. Distally, the clavicle articulates with the acromion process of the scapula, a large triangular flat bone in the back of the shoulder. The glenoid cavity of the scapula articulates with the head of the humerus.

The most striking difference between the chimpanzee and human shoulder is in the proportions of the scapula. Human arm strength, much less powerful in movements when in a raised position, is reflected in the shape of the scapula that provides attachment surfaces and lever arms for muscles (return to outline).

Arm

The upper arm is a single bone, the humerus. The forearm is formed medially by the ulna, which articulates firmly by a hinge joint to the humerus, and laterally by the radius which is firmly attached to the hand. The radius pivots on the humerus and ulna to supply hand rotation (pronation) and is attached to the ulna by powerful interossesous muscles and ligaments.

The head of the humerus is useful in identification of gender of a mature unknown cadaver. If the maximum diameter of the head is greater than 45 mm, the individual is probably male. If the head diameter is less that 42 mm, it is probably female.

The chimpanzee distal humerus contrasts with the human. The human lacks the robust lateral supracondylar ridge, a high and robust lateral epicondyle, and the steep, sharp, lateral margin of the olecranon fossa . The chimpanzee forearm is relatively long in comparison to humans . Chimp radius and ulna are more curved than in humans and the chimpanzee distal radius has a radiocarpal joint surface that diverges medially. The major differences between human and chimpanzee limbs are contrasts in relative proportion. Chimpanzees have large powerful arms, slightly longer than their very short legs. Human arms are about 70% as long as human legs.

Long bone indices of Humans and Chimpanzees

[ From Aiello and Dean 1990, Pp. 249]

 

 Species  Intermembral Index  Humerofemoral Index  Brachial Index  Crural Index
 Human (male)  69.7  71.4  77.9  82.4
 Human (female)  68.5   69.8  77.0  81.3
 Chimpanzee (male)  108.0  101.1   91.9  79.8
 Chimpanzee (female)  109.4  102  92.4   80.4
 Pygmy chimpanzee (male & female)   102.2  98.0  91.9  82.6


where:
Intermembral index = [(humerus + radius) x 100]/)femur + tibia)
Humerofemoral index = (humerus x 100)/femur
Brachial index = (radius x 100)/humerus
Crural index = (tibia x 100)/femur

(return to outline)

Hand

The hand has three skeletal regions: (1) The carpus, a series of eight carpals, form the wrist. (2) The hand consists of five metacarpal bones. (3) Phalanges form the skeleton of the fingers. The thumb, digit I has two phalanges (proximal & distal), while digits II through V have three phalanges (proximal, middle and distal).

The chimpanzee hand is notably different from the human hand in the relative length of its digits. The chimp thumb is much shorter than in humans, phalanges exhibit much more robust insertion areas for flexor tendons, and metacarpals have transverse ridges across their heads that limit dorsiflexion (return to outline).

Pelvic Girdle

The pelvic girdle is formed by the sacrum, coccyx, and the two coxae. Each coxa is attached by strong ligaments to the sacrum and to each other at the pubic symphysis. A coxa is formed by the fusion of three bones, the ilium, ischium, and pubis, which meet in the acetabulum or hip socket.

The human female has a larger birth canal than does a male. Consequently there is a constellation of characters that can be used to identify the gender of an unknown pelvis. The pelvic inlet of females is larger and has a greater absolute circumference. The superior ramus of the pubic bone is longer, increasing the pubic/ischium ratio. The greater sciatic notch is wider and forms a longer angle. The increased pubic length and laterally displaced ischia result in a wider subpubic angle. The growth and remodeling of the pubis produces extra bone at the symphysis, leaving a concave inferior ramus, a ventral arc that represents a previous border of the symphysis, and a narrow inferior pubic ramus. The female pubic symphysis is likely to be longer in its superior-inferior diameter and smaller in its dorsal-ventral diameters than is that of a male. Females are more likely to have a well-developed preauricular sulcus, and those who have borne children may have pits or guttering along the dorsal border of the pubic symphysis. Since they have smaller femurs, females have smaller acetabula.

(After Schultz 1949 and A & D 1990
 Species  n  Mean  Min  Max
 Human (male)  50  79.9   71.0   88.0
 Human (female)  50  95.0  84.0  106.0
 Chimpanzee (male)  21  86.2  69.7  95.2
 Chimpanzee (female)  30  87  78.9   98.9

 

Differences in the pelvis reflect the differences between the habitual bipedal locomotion of humans and quadrupedal movements of chimps . The pelvis of the two primates have radically different form and locomotor function. The relative width of the iliac blade (width/length x 100) is much larger in humans (125.5) than in chimpanzees (66.0). The human ilium is broad and low, while the chimp ilium is narrow and high. The human has a barely noticeable iliac pillar or thickening which extends from the iliac tubercle to the acetabulum. The human has an anterior inferior iliac spine. The human acetabulum is larger, reflecting the larger head of the femur, and the superior border of the acetabulum is reinforced to sustain the pressure of bipedal walking. The inferior border of the ilium near the auricular surface forms a greater sciatic notch in humans. The auricular surface is larger in the human. The ape sacrum is long and narrow (return to outline).

Leg

The femur, the bone in the thigh, articulates ball and socket fashion in the acetabulum of the coxa. The lower leg contains a large medial bone, the tibia, which articulates with the femoral condyles to form the knee. Lateral to the tibia, the fibula is a small, irregular bone that provides attachment surfaces for muscles. Projections on the distal ends of tibia and fibula, the medial and lateral malleolus, form a secure slotted proximal structure for the ankle joint.

As in the head of the humerus, a maximum diameter of 45mm or greater for the femur head indicates a male gender.

The human femur is longer than the chimp femur and usually has an elevated pilaster that supports the linea aspera down the shaft. The angles of the head, shaft, and condyles contrast markedly with those of the ape. The load axis never intersects the shaft in a chimpanzee femur. The femoral condyles of the human are larger and more elliptical than are those of the chimp. The human femur has a larger articular surface and mid-shaft circumference when compared to the arm than does the chimpanzee. The chimpanzee has a similar ratio between femur length and tibia length but the chimpanzee leg (including both femur and tibia length) is much shorter relative to the arm. The chimpanzee proximal tibia is smaller, less well supported by the shaft, and has condyles than are more convex than is usual in humans(return to outline).

Foot

Like the hand, the foot has three anatomical regions: (1) The seven bones of the tarsus form the ankle and proximal half of the foot. (2) The middle portion of the foot consists of five metatarsals. (3) Phalanges, the skeletal elements of the toes, have the same number and arrangement as in the fingers.

The primary difference between the human and chimp foot is the contrast between prehensile functions of the ape foot and the anatomy of bipedal striding in the human. The chimpanzee foot has an opposable hallux and long phalanges. The human foot has greatly reduced digits, with all metatarsals parallel and an increase in the lever arm of the tarsus for striding. In the human foot, a longitudinal arch provides a shock absorbing and weight distribution system. The orientation of the ankle joint allows the tibia to take a straighter path over the foot during walking (return to outline).

Skeletal Maturation

The bones of the limbs and vertebral column are endochondral, that is, they are first formed as cartilage that is gradually replaced with bone. Centers of ossification in the cartilage gradually enlarge to form the bone. The body or shaft in long bones is called the diaphysis, or primary center of ossification. The ends of long bones have secondary centers of ossification, called epiphyses, that are separated from the diaphysis by cartilage plates. Eventually, the cartilage plates, the epiphyseal cartilage, are replaced by bone and the epiphyses unite with the diaphysis to form a single bone. The flat bones of the skull, mandible, and clavicles are intramembranous bones, formed from membranes, and generally do not have epiphyses (return to outline).

Locomotor Anatomy

Much of primate anatomy reflects habits of movement and commonly utilized substrate. Since the powerful legs of most primates are slightly longer than their arms, the pelvis is normally higher than the head when standing quadrupedally. However a few species exhibit extreme locomotor specialization, emphasizing arms for arm-swinging, legs for leaping, or arms and legs comparable in length for quadrupedal climbing or walking on the ground. Thus, limb length (Intermembral Index or IM = Length of Humerus + Radius x 100/ Length of Femur + Tibia) can serve as an index of the relative emphasis upon the arm versus the leg for propulsion:

1. Short limbs with leg and arm comparable - quadrupedal and arboreal

These animals walk on larger horizontal tree branches as if they were pathways. Short, usually robust, arms and legs lower their center of gravity. IM index is usually about 80 but approaches 100 in howler monkeys. Other characteristics include moderately sized fingers and toes; very prehensile hands and feet; and relatively mobile shoulder joints located and directed sternally on the thorax. Some species, especially those which perform spectacular leaping feats, have flexible, elongated backs (with extra vertebra) and powerful musculature associated with the back and hind limb. A few species in the Americas have somewhat prehensile tails that serve to anchor the animal when it feeds near the ends of branches.

2. Long limbs with leg and arm of equal length - quadrupedal and terrestrial

Terrestrial quadrupeds tend to have shortened digits and elongated, robust tarsal and metatarsal elements. IM index is above 90. The shoulder joint, lying alongside the narrow and laterally flattened thorax, is oriented toward the ground. The weak clavicular-sternal joint is easily dislocated from the segmented sternum. Arms and legs, modified for powerful sagittal motions, have a relatively small range of movement. The humerus bears a prominent deltoid process (the attachment surface for the M. deltoideus) and the ulna has a large olecranon process, the insertion point of the M. triceps brachii, a powerful forearm extensor. Hands are pronated when in contact with the ground. One species, the patas monkey, is digitigrade (like a cat), with specialized anatomy for terrestrial running in which only fingers and toes make contact with the ground.

3. Very long limbs with leg and arm of comparable length - quadrupedal and arboreal with an emphasis on quadrupedal climbing and suspension

A few primate species in the Family Lorisidae combine quadrupedal suspensory climbing with quadrupedal arborealism, requiring great joint mobility and wide range of movement. IM index is about 90. Their hands and feet are particularly prehensile.

4. Arm longer than leg - brachiation and arboreal

Brachiation (arm swinging) is a special form of locomotion in which the body is suspended below branches. It allows utilization of small branches near the fringe of a tree canopy since the brachiator is suspended beneath its handholds. In contrast, a large bodied quadruped that tries to walk on a small branch has difficulty balancing as the supporting tree limb bends. A brachiator can easily exploit the very fringe of a tree canopy by dispersing its weight to the ends of several branches. New World brachiators use their prehensile tail as a fifth prehensile limb to further disperse weight. Most rapid brachiation is attained by using gravity to convert vertical height to speed. IM index is 100 or above.

Brachiation generally is associated with major alterations in the arm, hand, and thorax. The shoulder joint is positioned laterally and cranially on a barrel-shaped thorax. Robust muscles attach to the sternum, vertebral column, head, and rib cage, stabilizing the shoulder. The more powerful the arm movements, the more robust the stabilizing musculature must be. The clavicle acts a strut to stabilize the shoulder joint against a sternum whose segments unite to form a single bone. This clavicular-sternal joint is very strong and is not easily dislocated. A relatively round head of the humerus reflects a very wide range of motion. Additional elbow strength results from a more distinct separation of the radius and ulna on the articular surfaces of the distal humerus. The olecranon process of the ulna is small, allowing full extension of robust forearms. Brachiators tend to have reduced thumbs. If a thumb is present, it is folded out of the way against the palm where it does not interfere with elongated fingers that hook or snag handholds. The lumbar region of the vertebral column is shortened and stabilized, and a very mobile hip joint allows the foot to grasp anchorage in a wide range of positions.

There are several types of brachiators. Gibbons and siamangs, who use arm swinging as a major means of travel, are the best brachiators. Chimpanzee, gorillas, and humans are capable of this type of brachiation, but do not practice it as a primary means of locomotion. The orangutan combines quadrupedal climbing and brachiation, but like chimpanzees and gorillas, is typically a terrestrial quadruped.

At least one New World primate, the spider monkey, practices a variation of brachiation in which the body is kept vertical while brachiation is performed by hands, feet and sometimes the tail. This requires unusually long legs and mobile hips. When moving at slower speeds or while feeding, the spider monkey behaves as an arboreal quadruped. Its tail is the most prehensile of any primate.

5. Arm longer than leg - quadrupedal knuckle-walking and fist walking

Knuckle-walking is quadrupedal locomotion with the hands pronated and fingers flexed resulting in dorsal surfaces of the middle phalanges contacting the ground, supporting the weight on the knuckles. Gorillas and chimpanzees are habitual knuckle-walkers, whereas orangutans usually move quadrupedally with the hand made into a fist. IM indexes for the chimpanzee, gorilla, and orangutan are 102, 116, and 139, respectively.

6. Leg longer than arm - leaping and arboreal

A special class of leaping locomotor behavior, in which the body is positioned vertically at rest, is called vertical clinging and leaping. It requires powerful hind limbs to propel the leap as well as to break the impact of landing. Most (but not all) vertical clinging and leaping species have a tail that is used maintain attitude control during leaps. Rapid movements are so well-coordinated during flight that the animal transits the crown of a tree without appearing to make contact with branches. This visual impression of suspending the laws of gravity fueled many "ghost" myths associated with vertical clinging and leaping primates. There is a tendency toward elongation of tarsal elements, especially calcaneus and navicular. Posterior elongation of tuberosity of the calcaneus serves as a robust lever arm for M. gastrocnemius and M. soleus, powerful flexors of the foot. The tendency for fusion of the tibia and fibula is fully expressed only in the tarsier. IM index is below 70.

7. Leg longer than arm - bipedalism

Though obligate bipedalism is found only among humans, many other primate species are capable of facultative bipedalism. Foot specializations for bipedalism include an enlarged and robust tarsal region, greatly reduced phalanges, and strong ligaments that bind tarsals and metatarsals into shock-absorbing longitudinal and transverse plantar arches. A large calcaneus tuberosity acts as a lever arm for plantar flexion. The most unique character of the long, robust legs is the placement of the knees (when in anatomical position) close to the median sagittal plane, functionally beneath the body's center of gravity. The knee itself is adapted to locking in full extension with deep groves to stabilize the patella, a bone that forms in tendons of the quadriceps muscle. The broadened hip becomes a primary weight-bearing joint, characterized by an enlarged femur head as a weight-bearing surface. Pelvic anatomy is dramatically rearranged. A relatively broad sacrum positioned above the hip joint transfers weight to femur head via a wide and robust illium. A shortened ischium places the ischial tuberosity relatively close to the acetabulum. The vertebrae, increasing in size progressively from skull to sacrum, are arranged in a ventral-dorsal S-shaped curve above the pelvis. Though free of locomotor tasks, the arm retains the range of movement seen in brachiators. IM index is 70.

8. Climbing by nails

Elongated and laterally compressed nails of callithricines have the functional attributes of claws. Although they climb by grasping small branches, they are able to use these specialized nails to cling to relatively flat, vertical surfaces of larger trees. IM index ranges from 70 to 80 (return to outline).

Primate Vision

Color vision is a primate characteristic that presumably reflects our arboreal ancestry. There two types of photoreceptors in the primate retina: rods which function better at low light levels (scotopic vision), and cones which respond to much higher light intensities (photopic vision). The eyes of most diurnal mammals have cones more numerous toward the center of the retina (the region of sharp focus) and more rods toward the periphery. Nocturnal primates have only rod photoreceptors in the retina. The retina of higher primates has a macula lutea (yellow spot) of cones. The fovea, a small depression in the center of the macula in which there is only a single layer of cones, is the area of keenest vision and the target of focusing by the lens.

Color vision is produced by photosensitive pigments that differentially absorb wavelengths. Color perception depends upon the relative degree to which each pigment is stimulated. Primates have three different pigments, producing trichromatic vision.

Anthropoid vision is stereoscopic; that is, the eyes are positioned forward, allowing an overlap of most of the fields of vision with the optic axes parallel. An object is focused on both retinas simultaneously. The optic nerve tracts that pass information from retina to the brain meet at the optic chiasma. In most vertebrates and marsupials the fibres of the optic nerves cross at the chiasma and pass to the opposite of the brain. However in mammals, some of the fibres do not cross over so information from each eye is processed on both hemispheres of the brain(return to outline).

FORENSIC ANTHROPOLOGY

 

The murder of George Parkman, M.D., in 1849 stimulated Oliver Wendell Holmes, Dean of Harvard Medical College, and Professor Jeffries Wyman, an anatomist at Harvard, to formulate a protocol for investigating fragments alleged to be from a cadaver found at the murder scene (Joyce and Stover, 1991; page 52):

1. Are the remains human?

2. Do they represent a single individual or the commingled remains of several?

3. When did death occur?

4. How old was the decedent?

5. What was the decedent's gender?

6. What was the decedent's race?

7. What was the decedent's stature?

8. Did the body exhibit any significant anomalies, signs of disease and injuries, or other characteristics sufficiently out of the ordinary to provide positive identification?

9. What was the cause of death?

10. What was the manner of death? (natural, accidental, homicide, suicide, or unknown)

This is pretty close to the list of questions that a modern forensic investigator would ask. Two cardinal rules must be added: 1) Maintain tight security and record keeping so there is no lapse or break in the chain of evidence that may be later used in court. 2) Follow carefully planned procedures so there is no loss of evidence or information. The material is usually determined to be human or not on the basis of the scientists' familiarity with human anatomy. If a burial site, an anthropologist or archaeologist may be asked to determine whether it is current or prehistoric. The first stages of investigation may be tedious excavation, using careful archaeological techniques to expose the material and recover all evidence. Normally the skeleton is fully exposed and carefully photographed in situ. If it is a body, degree of decomposition, type of insects present, and characteristics of the site may provide information about the length of time since burial.

Excavated material will be carefully packaged, transported to the laboratory, cleaned, and placed on a table in approximate anatomical position. The question of how many individuals are represented is answered by careful examination of the skeletal elements present. If there are a large number of bones and there are no repetitions (such as two right femurs), then it is unlikely that more than one person is present. The theoretical maximum number is the number of bones present (since each could have come from a different individual) and the theoretical minimum is the number of individual elements that are duplicated (two left femurs = two individuals). In addition to counting skeletal elements, each bone must carefully examined to determine if size, age, gender, and other characters coincide with interpretation of what constitutes an individual(return to outline).

Estimating the Age of the Individual

Age estimates are readily made from dental eruption. Dental attrition and dental loss may indicate older age categories among adults. Severe tooth wear is commonplace in prehistoric individuals. Skeletal maturation of epiphyses to diaphyses is an accurate guide to age. Though cranial suture closure is more variable, is useful for older age ranges). Many areas of the older adult skeleton undergo progressive deterioration that serves as useful indicators of age. The pubic symphysis and sternal ends of ribs are particularly useful. As living bone ages, there is a slight but cumulative loss of osteons, microscopic circular structures of bone that surround a haversian canal(return to outline).

Estimating the Gender of the Individual

A scientist working with a large sample of skeletons from a localized deme would be able to distinguish gender groups on the basis of size and robusticity. Males are 5-10% larger, heavier and more rugged. Females as a group tend to be more gracile and have finer muscle markings. However, when dealing with a single specimen from an unknown background, it is difficult to calibrate the judgment of what is large or robust. Further, it is extremely difficult to make accurate gender estimates on immature specimens since many distinguishing characters are evident only after adolescence. Size alone is always a risky guide.

The most dramatic differences between males and females are in the pelvis where sexual dimorphism reflects the compromise between childbirth and locomotion. Since the heads of the humerus and femur reflect body size, the diameter of these two features provides a crude but convenient guide:

< 41 mm = female

> 45 mm = male

A similar relationship works for the foot. If the maximum length of the os talus is greater than 52 mm, the individual is likely to be male.

The skull is often used as a guide to gender. Males tend to have larger and more robust faces, especially the supraorbital torus. If the upper border of the orbit has a knife-like margin, the individual is likely to be female. A large mastoid process is a male indicator. The male mandible tends to be larger, with an outward flaring gonial angle and a square chin. A female chin is more pointed.

The gender of a pelvis is recognizable in 90% of individuals by the ratio of the length of the ischium divided by the length of the pelvis (Washburn, 1948). A value greater than .9 indicates female (return to outline).

Estimating the Race of the Individual

The Office of Management and Budget has established a classification that is used in reporting federal statistics (Hoyme and Iscan, 1989). These categories are also likely to be used in law enforcement records and reports, but they represent bureaucratic categories, not scientific or anthropological classifications:

1. American Indian or Alaskan native

2. Asian or Pacific Islander

3. Black

4. Hispanic

5. White

Since American Indians are derived from Asian populations, it would require exceptional efforts and circumstances to distinguish between the first two groups. Likewise, many Hispanics have American Indian ancestry. Ethnic group is usually defined culturally and generations of immigrants to this country are not inhibited by geographic isolation from marrying persons from other groups. Consequently the forensic scientist must be very conservative. Usually the decisions are made on the basis of dichotomies such as "Asian/not Asian" or "Black/not Black". For example, presence or absence of shovel-shaped incisors would imply Asian or not Asian respectively (return to outline).

Discriminant Functions

A useful technique of estimating gender or biological affinity has been to examine cadavers of known age and background to develop measurements and computations that correctly distinguish gender and population differences. Unfortunately study samples tend to be from unusual populations (such as the unclaimed bodies from the morgue or bodies donated for medical dissection). Since it is very questionable that most such samples are comparable to present populations, such statistics are used only as a supplement or aid in estimation.

A scientist uses a discriminate function by taking the appropriate measurements carefully to the nearest millimeter. Each measurement is then multiplied by a coefficient specified in the function formula, and the computed products are added or subtracted (according to their sign). If this sum is above the value specified as sectioning point for that computation, the decision is yes, the estimate indicates membership in the group specified by that equation. For example the following formulas distinguish, with about 75% accuracy, between American Blacks and American Whites using measurements of the pelvis (Iscan, 1983).

For males:

Bi-iliac breadth(0.637219)-16.84043 = score

Transverse breadth (0.1303004)-15.34591 = score

 

For females:

Bi-iliac breadth(0.0604552)-16.0448 = score

Transverse breadth(0.1336859)-17.01109 = score

A score greater than zero indicates American white, the group whose pelvis is usually slightly larger (return to outline).

Estimation of Stature of the individual

Regression formulae have been devised from cadaver samples for estimating stature from measurements of long bones. The length of the bone (measured in cm) is substituted into an appropriate equation (after Trotter, 1970).


For White male

2.38(femur length) + 61.41 = stature + 3.27 cm

For White female

2.47(femur length) + 70.35 = stature + 3.94 cm

For Black male

2.11(femur length) + 86.02 = stature + 3.94 cm

For Black female

2.28(femur length) + 59.76 = stature + 3.41 cm
(return to outline)


Home | General | Research | Instruction | World
 
Table of Contents

 


15 Aug 2004
Department of Department of Anthropology, College of Liberal Arts , UT Austin
Comments to cbramblett@mail.utexas.edu