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R L Susman

Publications and source records attributed to R L Susman.

18 recordsLinked to original sources
PubMed2001

Recently identified postcranial remains of Paranthropus and early Homo from Swartkrans Cave, South Africa.

Fifteen newly recognized hominid postcranials from Swartkrans are described here and compared with a sample of previously described early hominids, African apes and modern humans. Ten of the new specimens are from Member 1. Two are from Member 2 and three are from Member 3. Nine of the fossils are referred to Paranthropus, three to Homo, and three specimens cannot be assigned at present. The collection of hominid postcranials from Members 1-3 at Swartkrans now numbers more than 70 specimens. With the description of two new, small femoral heads, SKW 19 and SK 3121, there are now four proximal femora from Swartkrans. When SK 82 and SK 97 are compared with SKW 19 and SK 3121, the two sets offer important insights into body size and sexual dimorphism in Paranthropus robustus.A new distal femur, SK 1896 and other bones attributed to Homo cf. erectus, indicate that male Homo were larger than Paranthropus at Swartkrans.

Animals↗
PubMed1998

Hand function and tool behavior in early hominids.

Prompted by the discovery of the Olduvai Hominid 7 hand (Homo habilis) in 1960, studies of primate hands were conducted in order to understand better the functional morphology of the earliest hominids and the evolution of tool behavior. Since Napier's work in the early 1960's, the hand bones of a number of other species have been recovered in East and South Africa. New hominid finds and a prolific archaeological record have broadened our perspective on the evolution of tool behavior in Australopithecus, Paranthropus, and early Homo. A debate is underway at this time on the questions of what exactly we can glean from the fossil record regarding the evolution of tool behavior and what are the best approaches to interpreting the evidence. I support the model of Napier that identified morphological correlates of precision and power grasping in the hands of extant primates and in early hominid hand bones. At the same time, I question both the underlying rationale and attempts to identify more subtle aspects of precision grasping, based on present evidence.

Animals↗
PubMed1995

Quantifying phalangeal curvature: an empirical comparison of alternative methods.

It has been generally assumed and theoretically argued that the curvature of finger and toe bones seen in some nonhuman primates is associated with cheiridial use in an arboreal setting. Assessment of such curvature in fossil primates has been used to infer the positional behavior of these animals. Several methods of quantifying curvature of bones have been proposed. The measure most commonly applied to phalanges is that of included angle, but this has come under some criticism. We consider various other approaches for quantifying phalangeal curvature, demonstrating that some are equivalent to use of included angle, but that one--normalized curvature moment arm (NCMA)--represents a true alternative. A comparison of NCMA to included angle, both calculated on manual and pedal proximal phalanges of humans, apes, some monkeys, and the Hadar fossils, revealed that these two different measures of curvature are highly correlated and result in very similar distributional patterns.

Animals↗
PubMed1994

Fossil evidence for early hominid tool use.

Although several Plio-Pleistocene hominids are found in association with stone and bone tools, it has been generally assumed that at any one time the hominid with the largest brain was the toolmaker. Fossils recovered over the last decade suggest that early hominids subsequent to 2.5 million years ago all might have used tools and occupied "cultural" niches. A test for humanlike precision grasping (the enhanced ability to manipulate tools) is proposed and applied to australopithecines and early Homo. The results indicate that tools were likely to have been used by all early hominids at around 2.0 million years ago. The earliest australopithecines, which predate the appearance of stone tools in the archaeological record, do not show signs of advanced precision grasping.

Animals↗
PubMed1991

Radius of Paranthropus robustus from member 1, Swartkrans formation, South Africa.

Recently recovered hominid postcrania from Member 1, Swartkrans Formation include the proximal and distal ends of a right radius attributed to a single individual of Paranthropus robustus. These fossils are essentially similar to Australopithecus afarensis, A. africanus, and P. boisei homologues. The head manifests an ape-like circumferentia articularis, and the distal end has prominent medial, dorsal, and lateral tubercles and a well developed brachioradialis crest, features also commonly exhibited by extant great apes. The volar set of the P. robustus radiocarpal joint, like that of Australopithecus homologues, more closely resembles the neutral condition exhibited by Homo than the greater flexion evinced by living apes. Compared with fossil and recent specimens of Homo, the configuration of the P. robustus radial head suggests enhanced stability against medial displacement during pronation and supination; the strong crest for the attachment of brachioradialis may attest to enhanced forearm flexor capability. In addition, this crest and the prominent dorsal tubercles may indicate enhanced hand extensor and, therefore, hand flexor capabilities. The differences in radial morphology between Paranthropus and Homo may relate to significant behavioral differences between these two synchronic taxa.

Animals↗
PubMed1989

New hominid fossils from the Swartkrans formation (1979-1986 excavations): postcranial specimens.

New postcranial fossils of Paranthropus robustus and Homo cf. erectus were recovered from Swartkrans from 1979 through 1986. These fossils are from Members 1, 2, and 3. The new fossils are described here along with their morphological affinities. Fossils that are assigned to Paranthropus indicate that the South African "robust" australopithecines engaged in tool behavior and were essentially terrestrial bipeds at around 1.8 Myr BP. The manual dexterity and bipedal locomotion of Paranthropus may have equaled that of Homo habilis in East Africa at approximately the same time.

Africa, Southern↗
PubMed1988

Hand of Paranthropus robustus from Member 1, Swartkrans: fossil evidence for tool behavior.

New hand fossils from Swartkrans (dated at about 1.8 million years ago) indicate that the hand of Paranthropus robustus was adapted for precision grasping. Functional morphology suggests that Paranthropus could have used tools, possibly for plant procurement and processing. The new fossils further suggest that absence of tool behavior was not responsible for the demise of the "robust" lineage. Conversely, these new fossils indicate that the acquisition of tool behavior does not account for the emergence and success of early Homo.

Animals↗
PubMed1988

New first metatarsal (SKX 5017) from Swartkrans and the gait of Paranthropus robustus.

A new complete hallucal metatarsal (SKX 5017) was recovered from the "lower bank" of Member 1 at Swartkrans (ca. 1.8 m.y. BP). The new metatarsal is attributed to Paranthropus robustus, the predominant hominid found in Member 1 (greater than 95% of hominid individuals). SKX 5017 is similar to Olduvai Hominid 8-H from bed I, Olduvai (ca. 1.76 m.y. BP), and both resemble humans most closely among extant hominoids. The base, shaft, and head of SKX 5017 suggest human-like foot posture and a human-like range of extension (= dorsiflexion) at the hallucal metatarsophalangeal joint, while at the same time the distal articular surface indicates that a human-like toe-off mechanism was absent in Paranthropus. The fossil evidence suggests that Homo habilis and Paranthropus may have attained a similar grade of bipedality at roughly 1.8 m.y. BP.

Animals↗
PubMed1984

Arboreality and bipedality in the Hadar hominids.

Numerous studies of the locomotor skeleton of the Hadar hominids have revealed traits indicative of both arboreal climbing/suspension and terrestrial bipedalism. These earliest known hominids must have devoted part of their activities to feeding, sleeping and/or predator avoidance in trees, while also spending time on the ground where they moved bipedally. In this paper we offer new data on phalangeal length and curvature, morphology of the tarsus and metatarsophalangeal joints, and body proportions that further strengthen the argument for arboreality in the Hadar hominids. We also provide additional evidence on limb and pedal proportions and on the functional anatomy of the hip, knee and foot, indicating that the bipedality practiced at Hadar differed from that of modern humans. Consideration of the ecology at Hadar, in conjunction with modern primate models, supports the notion of arboredality in these earliest australopithecines. We speculate that selection for terrestrial bipedality may have intensified through the Plio-Pleistocene as forests and woodland patches shrunk and the need arose to move increasingly longer distances on the ground. Only with Homo erectus might body size, culture and other factors have combined to 'release' hominids from their dependence on trees.

Adaptation, Biological↗
PubMed1983

The locomotor anatomy of Australopithecus afarensis.

The postcranial skeleton of Australopithecus afarensis from the Hadar Formation, Ethiopia, and the footprints from the Laetoli Beds of northern Tanzania, are analyzed with the goal of determining (1) the extent to which this ancient hominid practiced forms of locomotion other than terrestrial bipedality, and (2) whether or not the terrestrial bipedalism of A. afarensis was notably different from that of modern humans. It is demonstrated that A. afarensis possessed anatomic characteristics that indicate a significant adaptation for movement in the trees. Other structural features point to a mode of terrestrial bipedality that involved less extension at the hip and knee than occurs in modern humans, and only limited transfer of weight onto the medial part of the ball of the foot, but such conclusions remain more tentative than that asserting substantive arboreality. A comparison of the specimens representing smaller individuals, presumably female, to those of larger individuals, presumably male, suggests sexual differences in locomotor behavior linked to marked size dimorphism. The males were probably less arboreal and engaged more frequently in terrestrial bipedalism. In our opinion, A. afarensis from Hadar is very close to what can be called a "missing link." We speculate that earlier representatives of the A. afarensis lineage will present not a combination of arboreal and bipedal traits, but rather the anatomy of a generalized ape.

Animals↗
PubMed1982

The functional morphology of the accessory interosseous muscle in the gibbon hand: determination of locomotor and manipulatory compromises.

The evidence for two functional roles of M. accessorius interosseus can be adduced as follows: (1) abduction of the whole finger is clearly required to resist the force of the thumb against the index during pinch grasp (Fig. 4) and when greater resistance is applied to the food, activity increases in the muscle. (2) The muscle also flexes the metacarpophalangeal joint at the onset of grasp on the ladder rung. In hanging from the finger tips or from the cage top, with the metacarpophalangeal joints extended, the muscle goes silent. From the functional point of view, the name given by Huxley (1871) to the M. accessorius interosseus ('abductor tertii internodii secundi digiti') is perhaps the most appropriate one. For reasons of economy, however, we favour continued use of the nomen Musculus accessorius interosseus (Fitzwilliams, 1910) or accessory interosseous muscle. The name coined by Keith (1894; p. 299) which implies that this muscle is an extensor of the distal interphalangeal joint, and any suggestions that the muscle functions primarily to flex the proximal interphalangeal joint are less appropriate or in error. The EMG data reveal that the M. accessorius interosseus is primarily an abductor of the index finger in gibbons, and we suggest that it is a unique feature of lesser apes that has evolved in compensation for a deep thumb-index cleft and the loss of the radial moiety of the first dorsal interosseous muscle. The primary role of this specialized muscle is in thumb-index pinch grasping.

Animals↗
PubMed1980

EMG of the interosseous and lumbrical muscles in the chimpanzee (Pan troglodytes) hand during locomotion.

The interosseous, lumbrical, and extensor digitorum communis muscles of the hunan hand constitute a complex apparatus that acts to move and stabilize the fingaers during grasping and manipulation. A telemetered electromyographic study of these muscles in chimpanzees was undertaken to determine whether use of the hand in locomotion and to maintain postures might be associated with functional roles different from those in humans. The manual interossei of chimpanzees are recruited in metacarpophalangeal flexion and in rapid interphalangeal joint extension. Slow digital extension can be accomplished solely by the extensor digitorum communis and lumbricals. The highly variable activity of the interossei during knuckle-walking is compatible with their roles as ab/adductors and rotators, but such movements could not be accurately assessed. It is concluded that the generalized suspensory and specialized terrestrial locomotion of the chimpanzee is not associated with major changes in the function of the manual interossei and lumbricals.

Animals↗
PubMed1979

Comparative and functional morphology of hominoid fingers.

Comparisons of hominoid metacarpals and phalanges reveal differences, many of which are closely linked to locomotor hand postures. The African apes display features of the metacarpals and phalanges which distinguish them from the other Hominoidea. These features are most evident in digits III and IV. The orangutan hand is demonstrably less well adapted to knuckle-walking and is distinctive in its adaptation to power and hook grasping of vertical and horizontal supports, respectively. Orangutan fingers possess a "double-locking" mechanism (Napier, '60), and a slight ulnad shift in the axis of the hand which results in lengthened phalanges of ray IV. Hylobatid apes are more like orangutans in their finger morphology than any of the other Hominoidea, but exhibit unique features of their own. These include elongate phalanges of fingers II-V. Human metacarpals II-V form two sets composed of II-III, and IV-V. The heads of both metacarpals II and III are characterized by axial torsion. This reflects the enhanced manipulatory role of the third finger in humans. Human distal phalanges are unique in the development of pronounced apical tufts. Multivariate analysis of metacarpal III and proximal III yields variables that array the extant apes along an arboreal-terrestrial axis, from hylobatid apes to male gorillas. The positions of taxa on this discriminant concur with observations on the locomotion of free-ranging apes.

Animals↗
PubMed1979

Telemetered electromyography of flexor digitorum profundus and flexor digitorum superficialis in Pan troglodytes and implications for interpretation of the O. H. 7 hand.

The importance of knuckle-walking in the locomotor repertoire of African apes raises the possibility that the long digital flexors may be specially adapted more to meet the demands of ground quadrupedalism than those of suspension. To investigate this possibiltiy, the activities of the flexor digitorum superficialis and flexor digitorum profundus were studied by means of telemetered electromyography in three chimpanzees. Results clearly indicate that the fasciculi of the muscles to digits bearing weight in knuckle-walking are not called upon to contract in quadrupedal postures or in slow and moderately fast quadrupedal locomotion except to help clear the fingers from the ground as the forelimb begins its recovery stroke. At the most rapid speeds, a slight to moderate level of activity sometimes occurs in the latter half of stance phase. The long digital flexors display maximum and sustained activity during suspension. It is concluded that any role for these muscles in maintenance of stability at the metacarpophalangeal joints during knuckle-walking must be predominantly passive. Prominent markings for insertions of these muscles in a fossil hand (such as O.H. 7) suggest use of the forelimb in suspensory climbing behaviors.

Adaptation, Biological↗
PubMed1979

Functional and morphological affinities of the subadult hand (O.H. 7) from Olduvai Gorge.

Study of the O.H. 7 hand was based primarily on morphological comparisons with a large series of hand skeletons of extant hominoid primates. Most of the hand elements are fragmentary or have missing epiphyses and only comparisons based on qualitative morphological observations are possible. The distal phalanges are complete, however, and were analyzed metrically utilizing univariate and multivariate statistical techniques. To compensate for size differences among the Hominoidea a number of size adjustments were employed. None of the adjustments were totally satisfactory from theoretical and practical standpoints and none completely eliminated the influence of size. There is no entirely satisfactory procedure to eliminate size and it is advisable to use several techniques that are not closely related, to compare the results and interpret them with caution. In certain features the wrist and fingers resemble those of African apes; in others they are more like modern human hands; in still others they are unique. The scaphoid and the proximal articular surface of the trapezium retain ape-like features, as do the proximal and middle phalanges. The pollical carpometacarpal joint and the distal phalanges are closer in morphology to those of modern humans. The scaphoid, proximal phalanges and middle phalanges of rays II-V indicate a hand capable of a strong power grip. A number of features of the thumb and the distal phalanges suggest that the O.H. 7 individual was capable of more precise manipulation that extant apes. FLK NN-A, a first distal phalanx, does not closely resemble the first distal phalanx of any of the living Hominoidea. Multivariate distance analysis indicates, however, that it is closest in overall morphology to the pollical distal phalanx of modern humans. In some features not included in the metric analysis, FLK NN-A also resembles the hallucial distal phalanx of modern humans.

Age Factors↗
PubMedDate not supplied

Evolution of the human foot: evidence from Plio-Pleistocene hominids.

The human foot serves a dual role during locomotion. It functions at times as a mobile structure and at times as a rigid lever. The human foot shows the hallmarks of an arboreal heritage wherein the foot was primarily a grasping organ. Over the course of the human career the human foot has evolved an elaborate plantar aponeurosis, strong plantar ligaments, longitudinal arches, an enlarged musculus flexor accessorius, an adducted (non-opposable) hallux, a remodeled calcaneocuboid joint, a long tarsus, and shortened toes (II to V). Comparisons of the chimpanzee and human foot allow us to reconstruct the pathway of foot evolution. Fossil foot bones of Homo habilis, dated at 1.76 million years, are remarkably like those of modern humans. Foot bones from Hadar, dated at around 3.5 million years, are remarkably chimpanzee-like, with only incipient human traits. The surprising chimpanzee-like qualities of the Hadar fossils strongly support the use of living apes as models of ancestral pongidhominid morphotypes.

Adaptation, Biological↗
PubMedDate not supplied

Electromyographic studies of the human foot: experimental approaches to hominid evolution.

Theories about the functions of the foot muscles have centered on their role in arch support. Previous anatomical and electromyographic studies (reviewed herein) have demonstrated that the arches are normally maintained by bones and ligaments. This study reports an electromyographic investigation of five foot muscles (flexor digitorum longus, flexor digitorum brevis, flexor accessorius, abductor hallucis, and abductor digiti quinti) conducted on four humans. The three toe flexors act together to resist extension of the toes during the stance phase of locomotion. Despite the large flexor accessorius in humans, neither this muscle nor the flexor digitorum brevis are preferentially recruited over the flexor digitorum longus for any normal posture or locomotion. The abductors affect the mediolateral distribution of pressure by positioning the forefoot. We suggest that the foot muscles play an important role in positioning of the forces on the foot in both posture and locomotion. Future electromyographic experiments on human and ape foot muscles in conjunction with detailed studies of early hominid fossils promise to elucidate the pathways of human locomotor evolution.

Adult↗