A preliminary estimate of the age of the Gladysvale australopithecine site

Excavations conducted at the Gladysvale site in the Transvaal, South Africa during 1991 -1992 have revealed an abundant Plio-Pleistocene fossil fauna from the limeworks breccia dumps and in situ decalcified deposits. To date, over 600 specifically identifiable macro-mammalian specimens have been recovered including the remains of Australopithecus. These identifications have revealed that the Gladysvale site has an extremely diverse macro-mammalian faunal assemblage equal to many other South African Plio-Pleistocene fossil sites. Comparison of the Gladysvale macromammalian fauna with those of the other early hominid-associated sites in South Africa indicates an age for the deposit(s) at Gladysvale between 1.7- 2.5 m.a.. ln addition, the Kromdraai A macromammalian assemblage is considered to be closer in age to the Gladysvale assemblage than any other South African faunal assemblage.John Vorster, Norman Segal, David Pfeiffe

Opiate Drug Seeking and Addiction: The Influence of Sucrose Consumption on the Acquisition and Expression of Morphine-induced Conditioned Place Preferences (CPP)

Sucrose intake may lead to changes in brain and behavior similar to the effects of abused drugs. For example, sucrose may agonize endogenous opiate systems and modulate opiate-seeking behavior. Previous research reported equivocal outcomes where sucrose may either enhance (i.e., cross-sensitization) or attenuate (i.e., cross-tolerance) drug seeking as measured by morphine-induced CPP. The present experiment extends from past work and evaluated the impact of sucrose administered prior to place conditioning. Additionally, unique groups received sucrose prior to tests for CPP to measure sucrose influences on CPP expression. Sprague-Dawley rats (n=24) were assigned to sucrose (15% w/v) or water pre-exposure conditions. Subsequently, subjects received morphine place conditioning where morphine (10mg/kg) was administered on the initially non-preferred side of the apparatus. Three post-tests were conducted and, prior to each test, animals within each pre-exposure group (sucrose or water) received either sucrose or water. Factorial ANOVA was used to analyze data. Results showed robust morphine-induced CPP. Although animals in the sucrose pre-exposure condition displayed enhanced CPP, the outcomes were not statistically significant. The present findings support the value of CPP techniques to measure opiate drug-seeking behavior. Future work may discover the sufficient conditions for detecting sucrose cross-sensitization of morphine CPP

Mandibular ramus morphology and species identification in Australopithecus sediba.

The site of Malapa, South Africa, has produced fossil evidence from multiple individuals of Australopithecus sediba including the partial skeletons designated as MH1 (holotype) and MH2 (paratype). A recent article in this Journal presented the hypothesis that MH1 and MH2 are not one species but instead represent two different genera: Australopithecus and Homo, respectively. Here we briefly evaluate this claim. We review the evidence from across the skeleton that demonstrates that MH1 and MH2 represent a single species, and we highlight other fossil samples that show the same pattern of mandibular ramus variation as observed in MH1 and MH2. The evidence shows that there is no reason to separate MH1 and MH2 into different species or genera based upon mandibular ramus morphology. This case illustrates how misleading small fragments of anatomy can be, why researchers should not use such fragments particularly for species and genus-level diagnoses, and why it is essential to use all available evidence.Significance:This study shows that the mandibular variation that is present in fossils from Malapa attributed to Australopithecus sediba has parallels in both Australopithecus africanus and in Homo. This helps to demonstrate that mandibular form is not sufficient to provide evidence of species diagnosis, but also that the development and adaptations to diet in Au. sediba were overlapping with those present in other related species of hominins

Short-Term H-alpha Variability in M Dwarfs

We spectroscopically study the variability of H-alpha emission in mid- to late-M dwarfs on timescales of ~0.1-1 hr as a proxy for magnetic variability. About 80% of our sample exhibits statistically significant variability on the full range of timescales probed by the observations, and with amplitude ratios in the range of ~1.2-4. No events with an order of magnitude increase in H-alpha luminosity were detected, indicating that their rate is < 0.05 /hr (95% confidence level). We find a clear increase in variability with later spectral type, despite an overall decrease in H-alpha "activity" (i.e., L_{H-alpha}/L_{bol}). For the ensemble of H-alpha variability events, we find a nearly order of magnitude increase in the number of events from timescales of about 10 to 30 min, followed by a roughly uniform distribution at longer durations. The event amplitudes follow an exponential distribution with a characteristic scale of Max(EW)/Min(EW)}-1 ~ 0.7. This distribution predicts a low rate of ~ 10^{-6} /hr for events with (Max(EW)/Min(EW) > 10, but serendipitous detections of such events in the past suggests that they represent a different distribution. Finally, we find a possible decline in the amplitude of events with durations of > 0.5 hr, which may point to a typical energy release in H-alpha events for each spectral type (E_{H-alpha} ~ L_{H-alpha} x t ~ const). Longer observations of individual active objects are required to further investigate this possibility. Similarly, a larger sample may shed light on whether H-alpha variability correlates with properties such as age or rotation velocity.Comment: Accepted for publication in Ap

Chromospheric Variability in SDSS M Dwarfs. II. Short-Timescale H-alpha Variability

[Abridged] We present the first comprehensive study of short-timescale chromospheric H-alpha variability in M dwarfs using the individual 15 min spectroscopic exposures for 52,392 objects from the Sloan Digital Sky Survey. Our sample contains about 10^3-10^4 objects per spectral type bin in the range M0-M9, with a total of about 206,000 spectra and a typical number of 3 exposures per object (ranging up to a maximum of 30 exposures). Using this extensive data set we find that about 16% of the sources exhibit H-alpha emission in at least one exposure, and of those about 45% exhibit H-alpha emission in all of the available exposures. Within the sample of objects with H-alpha emission, only 26% are consistent with non-variable emission, independent of spectral type. The H-alpha variability, quantified in terms of the ratio of maximum to minimum H-alpha equivalent width (R_EW), and the ratio of the standard deviation to the mean (sigma_EW/), exhibits a rapid rise from M0 to M5, followed by a plateau and a possible decline in M9 objects. In particular, R_EW increases from a median value of about 1.8 for M0-M3 to about 2.5 for M7-M9, and variability with R_EW>10 is only observed in objects later than M5. For the combined sample we find that the R_EW values follow an exponential distribution with N(R_EW) exp[-(R_EW-1)/2]; for M5-M9 objects the characteristic scale is R_EW-1\approx 2.7, indicative of stronger variability. In addition, we find that objects with persistent H-alpha emission exhibit smaller values of R_EW than those with intermittent H-alpha emission. Based on these results we conclude that H-alpha variability in M dwarfs on timescales of 15 min to 1 hr increases with later spectral type, and that the variability is larger for intermittent sources.Comment: Submitted to ApJ; 20 pages, 15 figure

New evidence of the Giant Hyaena, Pachycrocuta brevirostris (Carnivora, Hyaenidae), from the Gladysvale Cave deposit (Plio-pleistocene, John Nash Nature Reserve, Gauteng, South Africa)

A well preserved cranium which represents the most complete skull of Pachycrocuta brevirostris (Carnivora, Hyaenidae) discovered in Africa, and a maxillary fragment from the Gladysvale Cave Deposit (John Nash Nature Reserve, Gauteng, South Africa) are described and compared to other fossil and extant hyaenid specimens from South Africa and Europe. In addition, some aspects of functional morphology in the hyaenid dentition are reconsidered and suggested to be directly related to the palaeoecological role of P. brevirostris.The Council's Research Committee, University of the Witwatersrand; National Research Foundation (NRF); Palaeo-Anthropology Scientific Trust (PAST); Swiss National Science FoundationGrant No. 31-43584.95;National Geographic Society; Adolph H. Schultz-Foundation; Georges & Antoine Claraz-Donatio

Short Gamma Ray Bursts: a bimodal origin?

Short-hard Gamma Ray Bursts (SGRBs) are currently thought to arise from gravitational wave driven coalescences of double neutron star systems forming either in the field or dynamically in globular clusters. For both channels we fit the peak flux distribution of BATSE SGRBs to derive the local burst formation rate and luminosity function. We then compare the resulting redshift distribution with Swift 2-year data, showing that both formation channels are needed in order to reproduce the observations. Double neutron stars forming in globular clusters are found to dominate the distribution at z<0.3, whereas the field population from primordial binaries can account for the high-z SGRBs. This result is not in contradiction with the observed host galaxy type of SGRBs.Comment: 5 pages, 2 figures, accepted for publication in MNRA

A sabre-tooth felid from Coopers Cave (Gauteng, South Africa) and its implications for Megantereon (Felidae: Machairodontinae) taxonomy

Metrical and morphological analysis of a new sabre-tooth felid mandible recovered from the Plio-Pleistocene hominid-bearing site of Coopers, South Africa, indicates that it can be assigned to the genus Megantereon, though it is by some measures the smallest individual of this taxon yet described. Comparison of morphological variability within this genus to that found within four extant, medium-sized felid species (Acinonyx jubatus, Neofelis nebulosa, Panthera pardus and P. uncia) and the extinct genus Smilodon (sister taxon of Megantereon) provides confirmation of the suggestion by Martínez-Navarro&Palmqvist (1995, 1996) that Megantereon is a geographically polymorphic genus comprised of at least two species: M. cultridens (Cuvier, 1824) of North America and Europe and M. whitei (Broom, 1937) of Africa and Europe.Duke University’s Undergraduate Research Support Office, Howard Hughes Program and Department of Biological Anthropology and Anatomy; the Palaeo-Anthropology Scientific Trust (PAST); the National Geographic Society; and the Wenner-Gren Foundation (grant 6914 to D.J.D.

The postcranial skeletal maturation of Australopithecus sediba

OBJECTIVES: In 2008, an immature hominin defined as the holotype of the new species Australopithecus sediba was discovered at the 1.9 million year old Malapa site in South Africa. The specimen (MH1) includes substantial post-cranial skeletal material, and provides a unique opportunity to assess its skeletal maturation. METHODS: Skeletal maturity indicators observed on the proximal and distal humerus, proximal ulna, distal radius, third metacarpal, ilium and ischium, proximal femur and calcaneus were used to assess the maturity of each bone in comparison to references for modern humans and for wild chimpanzees (Pan troglodytes). RESULTS: In comparison to humans the skeletal maturational ages for Au. sediba correspond to between 12.0 years and 15.0 years with a mean (SD) age of 13.1 (1.1) years. In comparison to the maturational pattern of chimpanzees the Au. sediba indicators suggest a skeletal maturational age of 9-11 years. Based on either of these skeletal maturity estimates and the body length at death of MH1, an adult height of 150-156 cm is predicted. DISCUSSION: We conclude that the skeletal remains of MH1 are consistent with an ape-like pattern of maturity when dental age estimates are also taken into consideration. This maturity schedule in australopiths is consistent with ape-like estimates of age at death for the Nariokotome Homo erectus remains (KMN-WT 15000), which are of similar postcranial immaturity to MH1. The findings suggest that humans may have distinctive and delayed post-cranial schedules from australopiths and H. erectus, implicating a recent evolution of somatic and possibly life history strategies in human evolution

Consistent Factorization of Jet Observables in Exclusive Multijet Cross-Sections

We demonstrate the consistency at the next-to-leading-logarithmic (NLL) level of a factorization theorem based on Soft-Collinear Effective Theory (SCET) for jet shapes in e+e- collisions. We consider measuring jet observables in exclusive multijet final states defined with cone and k_T-type jet algorithms. Consistency of the factorization theorem requires that the renormalization group evolution of hard, jet, and soft functions is such that the physical cross-section is independent of the factorization scale mu. The anomalous dimensions of the various factorized pieces, however, depend on the color representation of jets, choice of jet observable, the number of jets whose shapes are measured, and the jet algorithm, making it highly nontrivial to satisfy the consistency condition. We demonstrate the intricate cancellations between anomalous dimensions that occur at the NLL level, so that, up to power corrections that we identify, our factorization of the jet shape distributions is consistent for any number of quark and gluon jets, for any number of jets whose shapes are measured or unmeasured, for any angular size R of the jets, and for any of the algorithms we consider. Corrections to these results are suppressed by the SCET expansion parameter lambda (the ratio of soft to collinear or collinear to hard scales) and in the jet separation measure 1/t^2 = tan^2(R/2)/tan^2(psi/2), where psi is the angular separation between jets. Our results can be used to calculate a wide variety of jet observables in multijet final states to NLL accuracy.Comment: 8 pages, 1 figure, uses elsarticle.cls; v2: minor edits, added reference