Pliocene hominid gait: New interpretations based on available footprint data from Laetoli

Normative trends in the gait patterns of modern man can be used to reconstruct crucial characteristics of the bipedal behaviour of Pliocene hominids from their fossilized footprints. In this reconstruction the interrelated parameters of velocity, stride-length, and cadence are determined from imprints made in damp volcanic ash some 3.7 million years ago. When early hominid footprint data is fitted to regression equations of high predictability for the interrelationship of these locomotor parameters in modern man, a pattern of gait emerges that contradicts previous reconstructions.     

Hominid teeth and their relationship to hominid phylogeny

Hominid fossil teeth are analyzed in terms of size and shape and contrasted with teeth from a modern population to determine boundaries that can be placed on a reconstruction of the hominid phylogeny. Teeth alone are considered as they are the only material preserved in large enough quantities to measure population variability accurately. Problems with the use of indices such as size and shape as species markers are discussed. Conclusions that are made about possible phylogenies are based on the analysis of size and shape.     

Affinities of the Swartkrans 847 hominid cranium

Further evidence of the presence of a second hominid species at the Swartkrans locality was obtained in 1969 when the SK.847 specimen was discovered by us to represent the same individual as the SK.80 maxilla. The SK.847 specimen had previously been regarded as robust australopithecine, whereas the latter was first attributed to Telanthropus capensis and subsequently to a species of the genus Homo. Recent criticism of our interpretation of these remains has not evaluated and analyzed critically the primary fossil evidence. Instead it relies on a strict adherence to an as yet unsubstantiated hypothesis that posits only a single hominid species at any point in space and time in the Cenozoic history of Hominidae.     

Gladysvale: First early hominid site discovered in South Africa since 1948

We report here the discovery of fossil hominid teeth at Gladysvale, near Johannesburg in the southern Transvaal. This find makes the site the seventh in South Africa to yield australopithecine remains and the first new early hominid-bearing locality to be found in this region since 1948. Apart from the hominid specimens, our excavations at Gladysvale have added appreciably to the abundant Plio-Pleistocene fauna previously recorded from the cave deposit. The fauna indicates that savanna conditions prevailed during deposition of at least part of the fill. Preliminary faunal dating gives an age of deposition of between c1.7 and c2.5 mya. © 1993 Wiley-Liss, Inc.     

Changes in the lower premolar-size sequence during hominid evolution. Physlogenetic implications

The size relationship between the crown area of the lower canines (Cs), third (P3s) and fourth premolars (P4s), and first molars (M1s) in hominids is examined by means of the regression analysis. The lower P3 seem to be under the influence of those factors that control both the size of the anterior and posterior teeth, and the P4:P3 size ratio is related to the relative size of the anterior and posterior dentitions. So, the P4>P3 sequence is associated with the megadontia and hipermegadontia of the posterior teeth, whereas the expansion of the anterior teeth produces the P3>P4 sequence. We consider the P4:P3 size ratio as an excellent indicator of the taxonomic and philogenetic status of fossil hominids.     

Stride length and speed for adults, children, and fossil hominids

Research workers studying the relationship between stride length (L) and speed (u) in human walking have often expressed their results as multiples of stature (h): they have given values of L/h and u/h. They have claimed or implied that this takes account of differences of body size and that L/h should be the same function of u/h for people of all sizes. It is shown that this is not true for comparisons of children with adults. Further, it is argued by dimensional analysis that u/square root gh is a more appropriate speed parameter that u/h (g is the acceleration of free fall). It is shown that L/h is approximately the same function of u/square root gh for children aged 4 or more years as for adults. The empirical relationship between L/h and u/square root gh is used to make new estimates of walking speed for the early hominid footprints found at Laetoli, Tanzania. The speeds obtained are equivalent to mean speeds of human walking observed in small towns (i.e., they give approximately equal values of u/square root gh).     

Early hominid enamel hypoplasia.

Enamel hypoplasia in the South African Plio-Pleistocene fossil hominid sample is examined. The Swartkrans hominids are shown to have a higher incidence of hypoplasia than the Sterkfontein hominids. Within the Swartkrans sample, individuals with hypoplasia of the first upper molar have lower-than-expected ages of death. Possible taphonomic explanations for these observations are discussed.     

The differential frequency of preservation of early hominid wrist and hand bones

A survey of hominid hand and wrist bones of Plio-Pleistocene fossil hominid sites in Africa was undertaken. There are 101 specimens in total, from 7 sites. Carpals are most rarely preserved, but certain elements such as the capitate tend to be more frequently preserved than others. There is a preservation rate cline from proximal to distal in the hand, proximal elements (metacarpals) being numerically better preserved than the distal elements (proximal, middle and distal phalanges, in that order of preservation). The proportion of complete, or nearly complete hand and wrist bones is greater in the distal than in the proximal elements. There is no statistical difference in the frequency of preservation of left and right sides, or in the frequency of preservation of proximal and distal ends of individual bones, although there is a tendency for proximal ends to occur more frequently than distal ends. The incidence of hand and wrist bones in fossil deposits is low compared with that of other post-cranial skeletal elements (with the exception of foot bones, where the incidence is similar). This could be accounted for by depositional factors, but preparation techniques and differential collection of specimens may play a role.     

The O.H. 7 (Olduvai Gorge,Tanzania) hominid partial brain endocast revisited

The O.H.7 brain endocast was reexamined using a stereoplotting apparatus to quantify the amount of distortion. Some 127 measurements for each of the left and right sides were taken and treated statistically by student t-tests, both in paired and grouped fashion. Grouped data indicated no significant left-right differences. Paired data suggested three small regions of distortion, which produced three pairs of left-right differences that were significantly different. Given the very local nature of these minor distortions, it is concluded that the original reconstruction by Tobias was essentially correct. In addition, multiple regression analyses of selected chord-arc dimensions suggest that a volume in excess of 700 ml is most probable.     

Multimale mating and absence of canine tooth dimorphism in woolly spider monkeys (Brachyteles arachnoides)

The relatively low degree of canine tooth dimorphism in Australopithecus afarensis has been used as “primary evidence” to support the concept of a mating system of monogamous pair-bonding and male provisioning. A recent field study of woolly spider monkeys shows that these large primates, which lack canine tooth (and body size) dimorphism, are characterized by apolygynous mating system. Male parental care of infants is absent in this species. These data support the view that a lack of canine tooth dimorphism in an anthropoid species does not necessarily imply either a monogamous, pair-bonded mating system or male parental care.     

Early hominid physical evolution

Hindrances against bipedalism evolution are localized in obstetrical constraints, maternal mortality rates, infant birth trauma and unsafe pregnancy. Analysis of infant survival probability shows that a shift to bipedalism could occur as a necessary consequence of the process of body fur reduction, in a balance between such hindrances and safe infant transportation. Fur reduction is proposed to correlate with cooling mechanism in intra-species physical fights. The triggering of a feed-back mechanism connecting reduction of body fur to canine reduction would be responsible for a passage from threat displays to actual physical fights. The proposed scenario for such changes is the transition from uni-male to multi-male social structures among Hominoidea. The implications of the approach adopted are discussed.     

Paleopediatrics: Or when did human infants really become human?

Modern human children take about twice as long as their closest biological relative, the chimpanzee, to mature. One standard explanation for the evolution of “delayed maturation” at an early stage of human evolution is that it provided the time necessary for immature individuals to learn complex skills, most notably those relating to tool-making abilities. However, after comparing dental maturational profiles of early hominids from South Africa (who apparently did make and use stone tools) (Susman [1994] Science 265:1570–1573) to those of extant humans and chimpanzees, we find no evidence to document an association between “delayed maturation” and tool-making abilities in the early stages of human evolution. This also suggests that the assumed association between prolonged childhood dependency and other behaviors often associated with the advent of tool-making such as cooperative hunting, food sharing, home bases, sexual division of labor, etc., is also suspect. Instead, we must look for other, or additional, selective pressures for the evolution of “delayed maturation,” which may postdate the australopithecine radiation. © 1995 Wiley-Liss, Inc.     

Pattern profile analysis of hominid and chimpanzee hand bones

In a study designed to complement morphological research on hominid hand bones, length and width measurements of the thumb, index, and middle rays were obtained from radiographs of modern human hands. These rays are primary in precision-gripping postures and are therefore the ones most relevant for investigating evolutionary changes in fine manipulation. Pattern profile analysis allows individuals or samples to be plotted against a reference sample in standard deviation units, or Z-scores. It provides an indication of how different measurements are from modern human averages, while taking into consideration the degree of variation present within modern human samples. A pattern profile for chimpanzees is clearly distinct from humans but quite similar to that of a bonobo, demonstrating the promise of pattern analysis. Partial pattern profiles of several of the more complete early hominid bones from Hadar, Swartkrans, and Olduvai (O.H. 7) are presented and compared. Hadar bones are long and wide at midshaft relative to articular widths; both body-size effects and functional differences are likely. Thumb distal phalanges from Swartkrans and Olduvai both have relatively small base widths, but they differ in other proportions. Two first metacarpals from Swartkrans show distinct patterns. The profiles of La Ferrassie I and Shanidar IV show the characteristically large Neanderthal distal phalanges. Profiles of Skhūl IV and P?edmost III are alike in some regions with reference to modern North American white males, though they are less similar overall than are those of the two Neanderthals. © 1995 Wiley-Liss, Inc.     

Cortical motor asymmetry and hominid feeding strategies

Homo sapiens differs from all other primates in having a cerebrum that is markedly asymmetrical for a number of functions, including motor control of the hands. The ability to coordinate the two hands while each is engaged in a different task is not highly developed in non-human primates and may have been an important behavioral distinction between early apes and hominids. These skills are necessary for tool-making, and probably arose selectively as a feeding strategy to exploit an expanding food base. It is proposed that bimanual motor asymmetry follows bipedalism but precedes tool-making as a step in the process of hominization.     

Early hominid body weight and encephalization

The body weight of the Plio-Pleistocene hominids of Africa is estimated by predicting equations derived from the Terry Collection of human skeletons with known body weights. About 50% of the variance in body weight can be accounted for by vertebral and femoral size. Predicted early hominid weights range from 27.6 kg (61 lb) to 54.3 kg (119 lb). The average weight for Australopithecus is 43.2 kg (95 lb) and for Homo sp. indet. from East Rudolf, Kenya, is 52.8 kg (116 lb). These estimates are consistent even if pongid proportions are assumed. Indices of encephalization show that the brain to body weight ratio in Australopithecus is above the great ape averages but well below Homo sapiens. The Homo sp. indet. represented by the KNM-ER 1470, O.H. 7 and O.H. 13 crania have encephalization indices above Australopithecus despite the greater body weight of the former.     

Some comments on the case for Early Pleistocene hominids in South-Eastern Spain

Several sites in the Orce Basin have revealed evidence of the presence of hominids in the Early Pleistocene. These remains are dated to over 1.0 million years, while they may be as old as 1.6 million years. The skeletal remains from Venta Micena in the Orce Basin show a molecular “fossil protein” pattern which aligns them with hominids, but not with equids. This is supported by the anatomical evidence of the two humeral shafts from theEstrato Blanco in the Venta Micena deposits. The biparieto-occipital partial calvaria shows some unusual features if VM-0 is a hominid specimen. the presence of a prominent crest on the internal surface of the occipital fragment adjacent to the point lambda is decidedly unusual for a modern human calvaria. Moreover, theimpressions gyrorum, in the region where the superior parietal lobule of the cerebral hemisphere abutted against the calvaria, point to a bipartite superior parietal lobule with anterior and posterior moieties which, on the endocast, are clearly separated by a depression that represents a sulcus. These morphological traits are rather puzzling if VM-0 is a hominid, and at first they led me to hesitate over the anatomical identification of VM-0. However, the studies of Campillo (1989) and of Campillo and Barcelo (1986) suggest that the features of the fragment VM-0 are compatible with those of a hominid. Because I believe that we do not possess sufficient information on the variability of the endocranial and ectocranial manifestations of the sagittal suture and of its variance with age of the individual, in different hominid species and different equid species, I have not adduced this pattern as evidence in support or rebuttal of the hominid status of VM-0.     

The molecular mechanisms and factors affecting the feeding habits of silkworm (Lepidoptera: Bombyxidae)

Food is critical to the survival and development of insects. Bombyx mori (Lepidoptera: Bombycidae), a Lepidoptera model insect with economic significance, is a well-known oligophagous insect that mainly feeds on mulberry leaves. The feeding characteristics of this particular species provide an excellent model for studying the food selection of insect host plants. In recent years, there has been an increasing number of studies on the factors affecting the feeding of silkworms, especially with the development of molecular technology. Many mysteries have been gradually solved. This paper summarizes and discusses the factors that affect the feeding of silkworms, with a focus on the molecular mechanisms of silkworm feeding. It is hoped that this work will be helpful for further research on artificial diets for silkworms and disease control in lepidopteran insects.     

Prey capture phase of feeding behavior in the pteropod mollusc,clione limacina: neuronal mechanisms

The prey capture phase of feeding behavior in the pteropod mollusc Clione limacina consists of an explosive extrusion of buccal cones, specialized structures which are used to catch the prey, and acceleration of swimming with frequent turning and looping produced by tail bend. A system of neurons which control different components of prey capture behavior in Clione has been identified in the cerebral ganglia. Cerebral B and L neurons produce retraction of buccal cones and tightening of the lips over them — their spontaneous spike activities maintain buccal cones in the withdrawn position. Cerebral A neurons inhibit B and L cells and produce opening of the lips and extrusion of buccal cones. A pair of cerebral interneurons C-BM activates cerebral A neurons and synchronously initiates the feeding motor program in the buccal ganglia. Cerebral T neurons initiate acceleration of swimming and produce tail bending which underlies turning and looping during the prey capture. Both tactile and chemical inputs from the prey produce activation of cerebral A and T neurons. This reaction appears to be specific, since objects other than alive Limacina or Limacina juice do not initiate activities of A and T neurons.     

The scaling of tongue projection in the veiled chameleon,Chamaeleo calyptratus

Within a year of hatching, chameleons can grow by up to two orders of magnitude in body mass. Rapid growth of the feeding mechanism means that bones, muscles, and movements change as chameleons grow while needing to maintain function. A previous morphological study showed that the musculoskeletal components of the feeding apparatus grow with negative allometry relative to snout–vent length (SVL) in chameleons. Here, we investigate the scaling of prey capture kinematics and muscle physiological cross-sectional area in the veiled chameleon, Chamaeleo calyptratus. The chameleons used in this study varied in size from approximately 3 to 18 cm SVL (1–200 g). Feeding sequences of 12 chameleons of different sizes were filmed and the timing of movements and the displacements and velocities of the jaws, tongue, and the hyolingual apparatus were quantified. Our results show that most muscle cross-sectional areas as well as tongue and hyoid mass scaled with isometry relative to mandible length, yet with negative allometry relative to SVL. Durations of movement also scaled with negative allometry relative to SVL and mandible length. Distances and angles generally scaled as predicted under geometric similarity (slopes of 1 and 0, respectively), while velocities generally scaled with slopes greater than 0 relative to SVL and mandible length. These data indicate that the velocity of jaw and tongue movements is generally greater in adults compared to juveniles. The discrepancy between the scaling of cross-sectional areas versus movements suggests changes in the energy storage and release mechanisms implicated in tongue projection.