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PubMed2006

Community mercury levels in the vicinity of peri-urban waste disposal sites and fossil fuel burning operations.

INTRODUCTION: A study was conducted as a result of concern about mercury absorption amongst residents of a peri-urban area in Cape Town, South Africa, in close proximity to waste disposal sites and an industrial area. STUDY METHODS: The study compared urine mercury concentrations in a random sample of adult residents and children in both the formal and informal housing settlements of the "exposure" area (n = 90) and a control area (n = 90). A short questionnaire elicited demographic, lifestyle and medical details and possible occupational, household and environmental mercury exposures. RESULTS: The two samples were comparable with respect to background and potential confounding variables. The prevalence of urinary mercury levels>or=the WHO reference range in the exposure area was also higher than that in the control area (13% vs. 0%). The median urinary mercury concentrations in both study areas were below the World Health Organisation (WHO) reference level of 5.0 microg/g creatinine. The median level in the exposure area was slightly, but statistically significantly, higher than in the control area (1.1 vs. 0.25 microg/g creatinine), and the excess persisted after controlling for known possible mercury exposures. CONCLUSIONS: This is to our knowledge the first study of community inorganic mercury absorption in a developing country setting, and where airborne mercury was the exposure of concern. It was concluded that the health risk associated with the urinary mercury levels of residents in the exposure area was very low. However, low level environmental exposure in the area of concern could not be excluded.

Adolescent↗
PubMedDate not supplied

The effect of lower limb length on the energetic cost of locomotion: implications for fossil hominins.

The consequences of the relatively short lower limbs characteristic of AL 288-1 have been widely discussed, as have the causes and consequences of the short limbs of Neanderthals. Previous studies of the effect of limb length on the energetic cost of locomotion have reported no relationship; however, limb length could have accounted for as much as 19% of the variation in cost and gone undetected (Steudel and Beattie, 1995; Steudel, 1994, 1996). Kramer (1999) and Kramer and Eck (2000) have recently used a theoretical model to predict the effect of the shorter limbs of early hominids, concluding that the shorter limbs may actually have been energetically advantageous. Here, we took an experimental approach. Twenty-one human subjects, of varying limb lengths, walked on a treadmill at 2.6, 2.8, 3.0 and 3.2m.p.h., while their expired gases were analyzed. The subjects walked for 12 minutes at each speed and their rates of oxygen consumption (VO2) over four minutes were averaged to estimate VO2. We also measured each subject's height, weight and lower limb length. Lean body mass and % fat were determined using dual-energy x-ray absorptiometry. ANCOVA with total VO2 at either speed as the dependent variable and total lean mass, % fat and lower limb length as covariates resulted in all three covariates having a significant positive effect on VO2 at p<0.01. Subjects with relatively longer lower limbs had lower locomotor costs. Thus the short lower limbs characteristic of some hominid taxa would have resulted in more costly locomotion, barring some physiological anomaly. The magnitude of this effect is substantial; Neanderthals are estimated to have had locomotor costs 30% greater than those of contemporary anatomically modern humans. By contrast the increase in lower limb length seen in H. erectus would have mitigated the increase in locomotor costs produced by the increase in body size.

Adolescent↗
PubMed2004

Influences of limb proportions and body size on locomotor kinematics in terrestrial primates and fossil hominins.

During locomotion, mammalian limb postures are influenced by many factors including the animal's limb length and body mass. Polk (2002) compared the gait of similar-sized cercopithecine monkeys that differed limb proportions and found that longer-limbed monkeys usually adopt more extended joint postures than shorter-limbed monkeys in order to moderate their joint moments. Studies of primates as well as non-primate mammals that vary in body mass have demonstrated that larger animals use more extended limb postures than smaller animals. Such extended postures in larger animals increase the extensor muscle mechanical advantage and allow postures to be maintained with relatively less muscular effort (Polk, 2002; Biewener 1989). The results of these previous studies are used here to address two anthropological questions. The first concerns the postural effects of body mass and limb proportion differences between australopithecines and members of the genus Homo. That is, H. erectus and later hominins all have larger body mass and longer legs than australopithecines, and these anatomical differences suggest that Homo probably used more extended postures and probably required relatively less muscular force to resist gravity than the smaller and shorter-limbed australopithecines. The second question investigates how animals with similar size but different limb proportions differ in locomotor performance. The effects of limb proportions on gait are relevant to inferring postural and locomotor differences between Neanderthals and modern Homo sapiens which differ in their crural indices and relative limb length. This study demonstrates that primates with relatively long limbs achieve higher walking speeds while using lower stride frequencies and lower angular excursions than shorter-limbed monkeys, and these kinematic differences may allow longer-limbed taxa to locomote more efficiently than shorter-limbed species of similar mass. Such differences may also have characterized the gait of Homo sapiens in comparison to Neanderthals, but more experimental data on humans that vary in limb proportions are necessary in order to evaluate this question more thoroughly.

Animals↗
PubMed2004

The Mio-Pliocene European primate fossil record: dynamics and habitat tracking.

We present here a study of European Neogene primate occurrences in the context of changing humidity. We studied the differences of primate localities versus non-primate localities by using the mammal communities and the ecomorphological data of the taxa present in the communities. The distribution of primates is influenced by humidity changes during the whole Neogene, and the results suggest that the primates track the changes in humidity through time. The exception to this is the Superfamily Cercopithecoidea which shows a wider range of choices in habitats. All primate localities seem to differ from non-primate localities in that the mammal community structure is more closed habitat oriented, while in non-primate localities the community structure changes towards open-habitat oriented in the late Neogene. The differences in primate and non-primate localities are stronger during the times of deep environmental change, when primates are found in their preferred habitats and non-primate localities have faunas better able to adapt to changing conditions.

Animals↗
PubMed2005

Catarrhine primate divergence dates estimated from complete mitochondrial genomes: concordance with fossil and nuclear DNA evidence.

Accurate divergence date estimates improve scenarios of primate evolutionary history and aid in interpretation of the natural history of disease-causing agents. While molecule-based estimates of divergence dates of taxa within the superfamily Hominoidea (apes and humans) are common in the literature, few such estimates are available for the Cercopithecoidea (Old World monkeys), the sister taxon of the hominoids in the primate infraorder Catarrhini. To help fill this gap, we have sequenced the entire mitochondrial DNA (mtDNA) genomes from a representative of three cercopithecoid tribes, Cercopithecini (Chlorocebus aethiops), Colobini (Colobus guereza), and Presbytini (Trachypithecus obscurus), and analyzed these new data together with other catarrhine mtDNA genomes available in public databases. Molecular divergence date estimates are dependent on calibration points gleaned from the paleontological record. We defined criteria for the selection of good calibration points and identified three points meeting these criteria: Homo-Pan, 6.0 Ma; Pongo-hominines, 14.0 Ma; hominoid/cercopithecoid, 23.0 Ma. Because a uniform molecular clock does not fit the catarrhine mtDNA data, we estimated divergence dates using a penalized likelihood and a Bayesian method, both of which take into account the effects of rate differences on lineages, phylogenetic tree structure, and multiple calibration points. The penalized likelihood method applied to the coding regions of the mtDNA genome yielded the following divergence date estimates, with approximate 95% confidence intervals: cercopithecine-colobine, 16.2 (14.4-17.9) Ma; colobin-presbytin, 10.9 (9.6-12.3) Ma; cercopithecin-papionin, 11.6 (10.3-12.9) Ma; and Macaca-Papio, 9.8 (8.6-10.9) Ma. Within the hominoids, the following dates were inferred: hylobatid-hominid, 16.8 (15.0-18.5) Ma; Gorilla-Homo+Pan, 8.1 (7.1-9.0) Ma; Pongo pygmaeus pygmaeus-P. p. abelii, 4.1 (3.5-4.7) Ma; and Pan troglodytes-P. paniscus, 2.4 (2.0-2.7) Ma. These dates were similar to those found using penalized likelihood on other subsets of the data, but slightly younger than several of the Bayesian estimates.

Africa↗
PubMed2005

Molar microwear and dietary reconstructions of fossil cercopithecoidea from the Plio-Pleistocene deposits of South Africa.

The South African Plio-Pleistocene cave deposits have yielded a diverse cercopithecoid fauna. In this study, the possible dietary proclivities of these extinct species are examined using details of molar microwear. Although sample sizes are often small, wear patterns suggest possible temporal changes in the diets of Parapapio jonesi from Makapansgat to Sterkfontein, of Papio robinsoni from Sterkfontein to Swartkrans, and Cercopithecoides williamsi from Makapansgat to Sterkfontein to Swartkrans. However, there does not appear to have been a significant change in the dietary habits of Parapapio broomi over time. The microwear patterns of the two temporally successive congeners, Theropithecus darti and T. oswaldi show no significant differences from one another. The sympatric congeners, Parapapio broomi and Pp. jonesi, have microwear signatures that differ significantly at Makapansgat (Members 3 and 4) but not at Sterkfontein (Member 4). Finally, the microwear analyses suggest that the extinct cercopithecoid species did not necessarily have diets similar to those of their closest living relatives.

Animals↗
PubMed2005

Do homoiologies impede phylogenetic analyses of the fossil hominids? An assessment based on extant papionin craniodental morphology.

Homoiologies are phylogenetically misleading resemblances among taxa that can be attributed to phenotypic plasticity. Recently, it has been claimed that homoiologies are widespread in the hominid skull, especially in those regions affected by mastication-related strain, and that their prevalence is a major reason why researchers have so far been unable to obtain a reliable estimate of hominid phylogeny. To evaluate this "homoiology hypothesis", we carried out analyses of a group of extant primates for which a robust molecular phylogeny is available-the papionins. We compiled a craniometric dataset from measurements that differ in their susceptibility to mastication-related strain according to developmental considerations and experimental evidence. We used the coefficient of variation and analysis of variance with post hoc least significant difference comparisons in order to evaluate the variability of the measurements. The prediction from the homoiology hypothesis was that dental measurements, which do not remodel in response to strain, should be less variable than low-to-moderate-strain measurements, and that the latter should be less variable than high-strain measurements. We then performed phylogenetic analyses using characters derived from the measurements and compared the resulting phylogenetic hypotheses to the group's consensus molecular phylogeny. The prediction was that, if the homoiology hypothesis is correct, the agreement between the craniometric and molecular phylogenies would be best in the analyses of dental characters, intermediate in the analyses of low-to-moderate-strain characters, and least in the analyses of high-strain characters. The results of this study support the suggestion that mastication-related mechanical loading can result in variation in hominid cranial characters. However, they do not support the hypothesis that homoiology is a major reason why phylogenetic analyses of hominid crania have so far yielded conflicting and weakly supported hypotheses of relationship. These findings are consistent with a recent test of the homoiology hypothesis using craniodental data from extant hominoids, and cast doubt on the validity of the homoiology hypothesis, as originally formulated.

Animals↗
PubMed2005

The spermatozoon of a 'living fossil': Tubiluchus troglodytes (Priapulida).

The spermatozoon of Tubiluchus troglodytes, the first priapulid formally described from the Mediterranean Sea has a head composed of an acrosome and a nucleus. The acrosome is divided in two branches coiled around the nucleus. The nucleus is basally columnar, but apically generates two rods helically coiled one around the other. The midpiece is formed by an axoneme with 27 accessory microtubules, surrounded by three mitochondria. An annulus separates the midpiece from the tail that contains a 9 + 2 axoneme surrounded by nine accessory microtubules. The spermatozoon of T. troglodytes is similar to that of the other two species known from the genus, and completely different from the 'primitive' one of the other priapulids. Since Tubiluchus is considered the most basal of the extant priapulids, and the only genus with an internal fertilization, it may be that in priapulids the external fertilization is a derived character.

Acrosome↗
PubMed2003

Mediolateral reaction forces and forelimb anatomy in quadrupedal primates: implications for interpreting locomotor behavior in fossil primates.

The forelimb joints of terrestrial primate quadrupeds appear better able to resist mediolateral (ML) shear forces than those of arboreal quadrupedal monkeys. These differences in forelimb morphology have been used extensively to infer locomotor behavior in extinct primate quadrupeds. However, the nature of ML substrate reaction forces (SRF) during arboreal and terrestrial quadrupedalism in primates is not known. This study documents ML-SRF magnitude and orientation and forelimb joint angles in six quadrupedal anthropoid species walking across a force platform attached to terrestrial (wooden runway) and arboreal supports (raised horizontal poles). On the ground all subjects applied a lateral force in more than 50% of the steps collected. On horizontal poles, in contrast, all subjects applied a medially directed force to the substrate in more than 75% of the steps collected. In addition, all subjects on arboreal supports combined a lower magnitude peak ML-SRF with a change in the timing of the ML-SRF peak force. As a result, during quadrupedalism on the poles the overall SRF resultant was relatively lower than it was on the runway. Most subjects in this study adduct their humerus while on the poles. The kinetic and kinematic variables combine to minimize the tendency to collapse or translate forelimbs joints in an ML plane in primarily arboreal quadrupedal primates compared to primarily terrestrial quadrupedal ones. These data allow for a more complete understanding of the anatomy of the forelimb in terrestrial vs. arboreal quadrupedal primates. A better understanding of the mechanical basis of morphological differences allows greater confidence in inferences concerning the locomotion of extinct primate quadrupeds.

Animals↗