Quantifying the relationship between bone and soft tissue measures within the rhesus macaques of Cayo Santiago.

OBJECTIVES: Interpretations of the primate and human fossil record often rely on the estimation of somatic dimensions from bony measures. Both somatic and skeletal variation have been used to assess how primates respond to environmental change. However, it is unclear how well skeletal variation matches and predicts soft tissue. Here, we empirically test the relationship between tissues by comparing somatic and skeletal measures using paired measures of pre- and post-mortem rhesus macaques from Cayo Santiago, Puerto Rico. MATERIALS AND METHODS: Somatic measurements were matched with skeletal dimensions from 105 rhesus macaque individuals to investigate paired signals of variation (i.e., coefficients of variation, sexual dimorphism) and bivariate codependence (reduced major axis regression) in measures of: (1) limb length; (2) joint breadth; and (3) limb circumference. Predictive models for the estimation of soft tissue dimensions from skeletons were built from Ordinary Least Squares regressions. RESULTS: Somatic and skeletal measurements showed statistically equivalent coefficients of variation and sexual dimorphism as well as high epiphyses-present ordinary least square (OLS) correlations in limb lengths (R2 >0.78, 0.82), joint breadths (R2 >0.74, 0.83) and, to a lesser extent, limb circumference (R2 >0.53, 0.68). CONCLUSION: Skeletal measurements are good substitutions for somatic values based on population signals of variation. OLS regressions indicate that skeletal correlates are highly predictive of somatic dimensions. The protocols and regression equations established here provide a basis for reliable reconstruction of somatic dimension from catarrhine fossils and validate our ability to compare or combine results of studies based on population data of either hard or soft tissue proxies.

Mechanical and morphometric approaches to body mass estimation in rhesus macaques: A test of skeletal variables.

OBJECTIVES: Estimation of body mass from skeletal metrics can reveal important insights into the paleobiology of archeological or fossil remains. The standard approach constructs predictive equations from postcrania, but studies have questioned the reliability of traditional measures. Here, we examine several skeletal features to assess their accuracy in predicting body mass. MATERIALS AND METHODS: Antemortem mass measurements were compared with common skeletal dimensions from the same animals postmortem, using 115 rhesus macaques (male: n = 43; female: n = 72). Individuals were divided into training (n = 58) and test samples (n = 57) to build and assess Ordinary Least Squares or multivariate regressions by residual sum of squares (RSS) and AIC weights. A leave-one-out approach was implemented to formulate the best fit multivariate models, which were compared against a univariate and a previously published catarrhine body-mass estimation model. RESULTS: Femur circumference represented the best univariate model. The best model overall was composed of four variables (femur, tibia and fibula circumference and humerus length). By RSS and AICw, models built from rhesus macaque data (RSS = 26.91, AIC = -20.66) better predicted body mass than did the catarrhine model (RSS = 65.47, AIC = 20.24). CONCLUSION: Body mass in rhesus macaques is best predicted by a 4-variable equation composed of humerus length and hind limb midshaft circumferences. Comparison of models built from the macaque versus the catarrhine data highlight the importance of taxonomic specificity in predicting body mass. This paper provides a valuable dataset of combined somatic and skeletal data in a primate, which can be used to build body mass equations for fragmentary fossil evidence.

Lack of evidence for coevolution between oxytocin receptor N-terminal variants and monogamy in placental mammals.

Oxytocin (OXT) is a neurohypophyseal hormone that influences a wide range of affiliative behaviors, such as pair-bonding and infant care, across mammals. The effects of OXT depend significantly on an adequate interaction with its receptor, OXTR. OXTR belongs to the G-protein coupled receptor family. The extracellular N-terminal domain of OXTR interacts with the linear C-terminal tail of OXT and is required for OXT binding. Across mammalian species there is a genetic diversity in OXTR terminal sequence. Previous work on primates has shown an association between OXTR phylogeny and monogamy. However, it is not clear whether this variation coevolved with either mating system (monogamy) or infant care behaviors (such as allomaternal care). Here, we take a phylogenetic comparative and evolutionary modeling approach across a wide range of placental mammals (n = 60) to test whether OXTR N-terminal variants co-evolved with either monogamy or allomaternal care behaviors. Our results indicate that the diversity in OXTR N-terminal region is unlikely to provide the underlying genetic bases for variation in mating system and/or allomaternal behavior as we find no evidence for co-evolution between protein sequence and affiliative behaviors. Hence, the role played by OXT in influencing affiliative behaviors is unlikely to be mediated by the genetic diversity of its receptor.

Evolution of vertebral numbers in primates, with a focus on hominoids and the last common ancestor of hominins and panins.

The primate vertebral column has been extensively studied, with a particular focus on hominoid primates and the last common ancestor of humans and chimpanzees. The number of vertebrae in hominoids-up to and including the last common ancestor of humans and chimpanzees-is subject to considerable debate. However, few formal ancestral state reconstructions exist, and none include a broad sample of primates or account for the correlated evolution of the vertebral column. Here, we conduct an ancestral state reconstruction using a model of evolution that accounts for both homeotic (changes of one type of vertebra to another) and meristic (addition or loss of a vertebra) changes. Our results suggest that ancestral primates were characterized by 29 precaudal vertebrae, with the most common formula being seven cervical, 13 thoracic, six lumbar, and three sacral vertebrae. Extant hominoids evolved tail loss and a reduced lumbar column via sacralization (homeotic transition at the last lumbar vertebra). Our results also indicate that the ancestral hylobatid had seven cervical, 13 thoracic, five lumbar, and four sacral vertebrae, and the ancestral hominid had seven cervical, 13 thoracic, four lumbar, and five sacral vertebrae. The last common ancestor of humans and chimpanzees likely either retained this ancestral hominid formula or was characterized by an additional sacral vertebra, possibly acquired through a homeotic shift at the sacrococcygeal border. Our results support the 'short-back' model of hominin vertebral evolution, which postulates that hominins evolved from an ancestor with an African ape-like numerical composition of the vertebral column.

Knuckle-walking in Sahelanthropus? Locomotor inferences from the ulnae of fossil hominins and other hominoids.

Because the ulna supports and transmits forces during movement, its morphology can signal aspects of functional adaptation. To test whether, like extant apes, some hominins habitually recruit the forelimb in locomotion, we separate the ulna shaft and ulna proximal complex for independent shape analyses via elliptical Fourier methods to identify functional signals. We examine the relative influence of locomotion, taxonomy, and body mass on ulna contours in Homo sapiens (n = 22), five species of extant apes (n = 33), two Miocene apes (Hispanopithecus and Danuvius), and 17 fossil hominin specimens including Sahelanthropus, Ardipithecus, Australopithecus, Paranthropus, and early Homo. Ulna proximal complex contours correlate with body mass but not locomotor patterns, while ulna shafts significantly correlate with locomotion. African apes' ulna shafts are more robust and curved than Asian apes and are unlike other terrestrial mammals (including other primates), curving ventrally rather than dorsally. Because this distinctive curvature is absent in orangutans and hylobatids, it is likely a function of powerful flexors engaged in wrist and hand stabilization during knuckle-walking, and not an adaptation to climbing or suspensory behavior. The OH 36 (purported Paranthropus boisei) and TM 266 (assigned to Sahelanthropus tchadensis) fossils differ from other hominins by falling within the knuckle-walking morphospace, and thus appear to show forelimb morphology consistent with terrestrial locomotion. Discriminant function analysis classifies both OH 36 and TM 266 with Pan and Gorilla with high posterior probability. Along with its associated femur, the TM 266 ulna shaft contours and its deep, keeled trochlear notch comprise a suite of traits signaling African ape-like quadrupedalism. While implications for the phylogenetic position and hominin status of S. tchadensis remain equivocal, this study supports the growing body of evidence indicating that S. tchadensis was not an obligate biped, but instead represents a late Miocene hominid with knuckle-walking adaptations.

A milk-sharing economy allows placental mammals to overcome their metabolic limits.

SignificanceHere, we demonstrate that a naturally evolving behavior (allonursing) has greater effect on reproductive power (mass per unit of time) and output (litter mass at birth) than does artificial selection (domestication). Additionally, we demonstrate the importance of resource optimization afforded by sociality (rather than resource abundance per se) in shaping a species' life history profile and its ability to overcome its own physiological constraints.

New fossils of Australopithecus sediba reveal a nearly complete lower back.

Adaptations of the lower back to bipedalism are frequently discussed but infrequently demonstrated in early fossil hominins. Newly discovered lumbar vertebrae contribute to a near-complete lower back of Malapa Hominin 2 (MH2), offering additional insights into posture and locomotion in Australopithecus sediba. We show that MH2 possessed a lower back consistent with lumbar lordosis and other adaptations to bipedalism, including an increase in the width of intervertebral articular facets from the upper to lower lumbar column ('pyramidal configuration'). These results contrast with some recent work on lordosis in fossil hominins, where MH2 was argued to demonstrate no appreciable lordosis ('hypolordosis') similar to Neandertals. Our three-dimensional geometric morphometric (3D GM) analyses show that MH2's nearly complete middle lumbar vertebra is human-like in overall shape but its vertebral body is somewhat intermediate in shape between modern humans and great apes. Additionally, it bears long, cranially and ventrally oriented costal (transverse) processes, implying powerful trunk musculature. We interpret this combination of features to indicate that A. sediba used its lower back in both bipedal and arboreal positional behaviors, as previously suggested based on multiple lines of evidence from other parts of the skeleton and reconstructed paleobiology of A. sediba.

One of the defining features of humans is our ability to walk comfortably on two legs. To achieve this, our skeletons have evolved certain physical characteristics. For example, the lower part of the human spine has a forward curve that supports an upright posture; whereas the lower backs of chimpanzees and other apes ­ which walk around on four limbs and spend much of their time in trees ­ lack this curvature. Studying the fossilized back bones of ancient human remains can help us to understand how we evolved these features, and whether our ancestors moved in a similar way. Australopithecus sediba was a close-relative of modern humans that lived about two million years ago. In 2008, fossils from an adult female were discovered at a cave site in South Africa called Malapa. However, the fossils of the lower back region were incomplete, so it was unclear whether the female ­ referred to as Malapa Hominin 2 (MH2) ­ had a forward-curving spine and other adaptations needed to walk on two legs. Here, Williams et al. report the discovery of new A. sediba fossils from Malapa. The new fossils are mainly bones from the lower back, and they fit together with the previously discovered MH2 fossils, providing a nearly complete lower spine. Analysis of the fossils suggested that MH2 would have had an upright posture and comfortably walked on two legs, and the curvature of their lower back was similar to modern females. However, other aspects of the bones' shape suggest that as well as walking, A. sediba probably spent a significant amount of time climbing in trees. The findings of Williams et al. provide new insights in to our evolutionary history, and ultimately, our place in the natural world around us. Our lower back is prone to injury and pain associated with posture, pregnancy and exercise (or lack thereof). Therefore, understanding how the lower back evolved may help us to learn how to prevent injuries and maintain a healthy back.

Homoplasy in the evolution of modern human-like joint proportions in Australopithecus afarensis.

The evolution of bipedalism and reduced reliance on arboreality in hominins resulted in larger lower limb joints relative to the joints of the upper limb. The pattern and timing of this transition, however, remains unresolved. Here, we find the limb joint proportions of Australopithecus afarensis, Homo erectus, and Homo naledi to resemble those of modern humans, whereas those of A. africanus, Australopithecus sediba, Paranthropus robustus, Paranthropus boisei, Homo habilis, and Homo floresiensis are more ape-like. The homology of limb joint proportions in A. afarensis and modern humans can only be explained by a series of evolutionary reversals irrespective of differing phylogenetic hypotheses. Thus, the independent evolution of modern human-like limb joint proportions in A. afarensis is a more parsimonious explanation. Overall, these results support an emerging perspective in hominin paleobiology that A. afarensis was the most terrestrially adapted australopith despite the importance of arboreality throughout much of early hominin evolution.

Increased variation in numbers of presacral vertebrae in suspensory mammals.

Restricted variation in numbers of presacral vertebrae in mammals is a classic example of evolutionary stasis. Cervical number is nearly invariable in most mammals, and numbers of thoracolumbar vertebrae are also highly conserved. A recent hypothesis posits that stasis in mammalian presacral count is due to stabilizing selection against the production of incomplete homeotic transformations at the lumbo-sacral border in fast-running mammals, while slower, ambulatory mammals more readily tolerate intermediate lumbar/sacral vertebrae. We test hypotheses of variation in presacral numbers of vertebrae based on running speed, positional behaviour and vertebral contribution to locomotion. We find support for the hypothesis that selection against changes in presacral vertebral number led to stasis in mammals that rely on dorsomobility of the spine during running and leaping, but our results are independent of running speed per se. Instead, we find that mammals adapted to dorsostability of the spine, such as those that engage in suspensory behaviour, demonstrate elevated variation in numbers of presacral vertebrae compared to dorsomobile mammals. We suggest that the evolution of dorsostability and reduced reliance on flexion and extension of the spine allowed for increased variation in numbers of presacral vertebrae, leading to departures from an otherwise stable evolutionary pattern.

Predicting difficult and traumatic lumbar punctures.

OBJECTIVE: The objective of this study is to determine if visual and tactile inspection of the spine is useful in the prediction of a difficult or traumatic lumbar puncture (LP). DESIGN: This was a prospective, observational, cohort study conducted in the emergency department (ED) on patients who were undergoing an LP. Physicians prospectively completed a structured data form that included information about the patient, number of prior LPs performed, their assessment of the LP difficulty, and the number of needlesticks required. A "difficult" LP and a "traumatic" tap were defined a priori. Chi2, t tests, and regression were used as appropriate; an independent statistician performed the statistical analysis. SETTING: The study was conducted at an urban university teaching hospital with an annual ED census of approximately 48,000 patients between November 1, 2002, and June 1, 2003. PATIENTS: The study population included a convenience sample of patients undergoing LP in the ED. RESULTS: Of the 148 patients enrolled, LP was difficult in 47 (32%) patients and traumatic in 23 (16%) patients. The percentage of patients that did not have a visible spine was significantly higher in the difficult and traumatic groups (P < .05). Among patients where the physician was unable to visualize the spine, there were significantly more difficult LPs (P < .05). CONCLUSION: It may be possible to predict which patients will have difficult or traumatic LPs before performing the procedure. Simple bedside assessments of spine visibility and palpability may assist in planning the approach to an LP in patients.

Does the presence of crystal arthritis rule out septic arthritis?

The objective of this study was to determine the incidence of septic arthritis in the presence of joint crystals. A retrospective study was conducted at a university tertiary care referral center. The study population included all patients with synovial fluid crystals in the joint aspirate sent to the laboratory during the 7-year study period. Septic arthritis was defined as a positive synovial culture. Of the 265 joint aspirates containing crystals, 183 (69.0%) contained gout crystals, 81 (30.6%) contained pseudogout crystals, and 1 (0.4%) contained both. Four (1.5%) of the aspirates had positive cultures. The mean synovial WBC of the 4 samples with concomitant crystals and septic arthritis was 113,000 (95% confidence interval [CI] 72,700-153,200), which was significantly higher than the entire population at 23,200 (95% CI 19,400-27,000; p < 0.01). Of note, all 4 patients with concomitant disease had significant co-morbidities and synovial WBC counts greater than 50,000. Septic arthritis and acute crystal-induced arthritis can occur simultaneously; there were 4 cases (1.5%) of concomitant disease in our study population. The presence of crystals cannot exclude septic arthritis with certainty.

Barriers to the use of outpatient enoxaparin therapy in patients with deep venous thrombosis.

OBJECTIVE: To establish a clinical pathway for outpatient enoxaparin therapy in deep venous thrombosis (DVT) and then characterize its implementation and barriers to use. PROCEDURE: Single institution, prospective, observational study of consecutive adult emergency department patients (age > or =18 years) who had a diagnosis of DVT. A clinical pathway was created to facilitate outpatient therapy with enoxaparin, and then all patients with DVT were enrolled and studied. RESULTS: A total of 97/98 (99%) eligible patients were enrolled. Among 97 patients, 29 (30%) were successfully started on the outpatient enoxaparin therapy approach. Of the 68 (70%) patients not started on the outpatient therapy, 19 (20%) patients had contraindications to anticoagulant therapy, 33 (34%) had other indications for hospitalization, 6 (6%) were unable to reliably self-inject, and 10 (10%) patients had a primary care physician or emergency physician who rejected the outpatient approach. CONCLUSIONS: The establishment of an organized DVT pathway for outpatient enoxaparin may facilitate home therapy; however, there will remain reasons that make hospital admission unavoidable in some patients.