Lee J. Arnold

Neandertal roots: Cranial and chronological evidence from Sima de los Huesos

Neandertal ancestors from Pleistocene Spain The Sima de los Huesos site in Atapuerca, northern Spain, is a rich source of fossil hominin specimens. The site has now yielded further skull specimens that illuminate patterns of human evolution in Europe nearly half a million years ago. Arsuaga et al. studied 17 crania, including 7 that are new specimens and 6 that are more complete than before (see the Perspective by Hublin). This assemblage of specimens reveals the cranial, facial, and dental features of the Atapuerca hominins, which allows more precise evolutionary positioning of these Neandertal ancestors. Science, this issue p. 1358; see also p. 1338 Seventeen skulls from at least 430 thousand years ago illuminate hominin evolutionary patterns in Pleistocene Europe. [Also see Perspective by Hublin] Seventeen Middle Pleistocene crania from the Sima de los Huesos site (Atapuerca, Spain) are analyzed, including seven new specimens. This sample makes it possible to thoroughly characterize a Middle Pleistocene hominin paleodeme and to address hypotheses about the origin and evolution of the Neandertals. Using a variety of techniques, the hominin-bearing layer could be reassigned to a period around 430,000 years ago. The sample shows a consistent morphological pattern with derived Neandertal features present in the face and anterior vault, many of which are related to the masticatory apparatus. This suggests that facial modification was the first step in the evolution of the Neandertal lineage, pointing to a mosaic pattern of evolution, with different anatomical and functional modules evolving at different rates.

Ancient DNA reveals late survival of mammoth and horse in interior Alaska

Causes of late Quaternary extinctions of large mammals (“megafauna”) continue to be debated, especially for continental losses, because spatial and temporal patterns of extinction are poorly known. Accurate latest appearance dates (LADs) for such taxa are critical for interpreting the process of extinction. The extinction of woolly mammoth and horse in northwestern North America is currently placed at 15,000–13,000 calendar years before present (yr BP), based on LADs from dating surveys of macrofossils (bones and teeth). Advantages of using macrofossils to estimate when a species became extinct are offset, however, by the improbability of finding and dating the remains of the last-surviving members of populations that were restricted in numbers or confined to refugia. Here we report an alternative approach to detect ‘ghost ranges’ of dwindling populations, based on recovery of ancient DNA from perennially frozen and securely dated sediments (sedaDNA). In such contexts, sedaDNA can reveal the molecular presence of species that appear absent in the macrofossil record. We show that woolly mammoth and horse persisted in interior Alaska until at least 10,500 yr BP, several thousands of years later than indicated from macrofossil surveys. These results contradict claims that Holocene survival of mammoths in Beringia was restricted to ecologically isolated high-latitude islands. More importantly, our finding that mammoth and horse overlapped with humans for several millennia in the region where people initially entered the Americas challenges theories that megafaunal extinction occurred within centuries of human arrival or were due to an extraterrestrial impact in the late Pleistocene.

Human occupation of northern Australia by 65,000 years ago

The time of arrival of people in Australia is an unresolved question. It is relevant to debates about when modern humans first dispersed out of Africa and when their descendants incorporated genetic material from Neanderthals, Denisovans and possibly other hominins. Humans have also been implicated in the extinction of Australia’s megafauna. Here we report the results of new excavations conducted at Madjedbebe, a rock shelter in northern Australia. Artefacts in primary depositional context are concentrated in three dense bands, with the stratigraphic integrity of the deposit demonstrated by artefact refits and by optical dating and other analyses of the sediments. Human occupation began around 65,000 years ago, with a distinctive stone tool assemblage including grinding stones, ground ochres, reflective additives and ground-edge hatchet heads. This evidence sets a new minimum age for the arrival of humans in Australia, the dispersal of modern humans out of Africa, and the subsequent interactions of modern humans with Neanderthals and Denisovans.

An arid-adapted middle Pleistocene vertebrate fauna from south-central Australia

How well the ecology, zoogeography and evolution of modern biotas is understood depends substantially on knowledge of the Pleistocene. Australia has one of the most distinctive, but least understood, Pleistocene faunas. Records from the western half of the continent are especially rare. Here we report on a diverse and exceptionally well preserved middle Pleistocene vertebrate assemblage from caves beneath the arid, treeless Nullarbor plain of south-central Australia. Many taxa are represented by whole skeletons, which together serve as a template for identifying fragmentary, hitherto indeterminate, remains collected previously from Pleistocene sites across southern Australia. A remarkable eight of the 23 Nullarbor kangaroos are new, including two tree-kangaroos. The diverse herbivore assemblage implies substantially greater floristic diversity than that of the modern shrub steppe, but all other faunal and stable-isotope data indicate that the climate was very similar to today. Because the 21 Nullarbor species that did not survive the Pleistocene were well adapted to dry conditions, climate change (specifically, increased aridity) is unlikely to have been significant in their extinction.

Population increase and environmental deterioration correspond with microlithic innovations in South Asia ca. 35,000 years ago

Genetic studies of South Asias population history have led to postulations of a significant and early population expansion in the subcontinent, dating to sometime in the Late Pleistocene. We evaluate this argument, based on new mtDNA analyses, and find evidence for significant demographic transition in the subcontinent, dating to 35–28 ka. We then examine the paleoenvironmental and, particularly, archaeological records for this time period and note that this putative demographic event coincides with a period of ecological and technological change in South Asia. We document the development of a new diminutive stone blade (microlithic) technology beginning at 35–30 ka, the first time that the precocity of this transition has been recognized across the subcontinent. We argue that the transition to microlithic technology may relate to changes in subsistence practices, as increasingly large and probably fragmented populations exploited resources in contracting favorable ecological zones just before the onset of full glacial conditions.

Headwater channel dynamics in semiarid rangelands, Colorado high plains, USA

Incised ephemeral channels provide a window into the fluvial processes that help sculpt rangeland landscapes. This paper presents observations of ephemeral channels and valley networks in the high plains of Colorado, USA, with an eye toward painting a picture of the ingredients that must be included in mathematical models of landscape evolution in such environments. Channel incision in the study area is driven by summer thunderstorms, which can with reasonable frequency (3–5 yr) generate boundary shear stresses high enough to penetrate the highly resistant vegetation armor, but only within erosional hot spots where hydraulic forces are amplified by channel constriction and locally steep gradients. Focusing of erosion at these hot spots (which correspond to knickpoints and channel heads) is amplified by the small areal footprint and short “erosional reach” of most convective storms. Upstream migration of knickpoints creates a pattern of short, active channel reaches separated by unchanneled or weakly channeled, fully vegetated stable reaches. Based on our observations, we interpret the necessary and sufficient conditions leading to the observed channel forms and dynamics as: (1) a resistant vegetation layer overlying an erodible substrate, which sets up a conditional instability through which erosional perturbations can grow by positive feedback; (2) high flow variability; (3) moderate to high substrate cohesion; and (4) a high volume fraction of fine-grained erodible material. Concave-upward valley long profiles are interpreted as a trade-off between downstream-increasing flood frequency and downstream-decreasing flood effectiveness. The observed process dynamics imply that long-term rates of valley incision should be especially sensitive to climatic oscillations between episodes of drought and warm-season convective rainfall.

Disruption of angiogenesis and tumor growth with an orally active drug that stabilizes the inactive state of PDGFRβ/B-RAF

Kinases are known to regulate fundamental processes in cancer including tumor proliferation, metastasis, neovascularization, and chemoresistance. Accordingly, kinase inhibitors have been a major focus of drug development, and several kinase inhibitors are now approved for various cancer indications. Typically, kinase inhibitors are selected via high-throughput screening using catalytic kinase domains at low ATP concentration, and this process often yields ATP mimetics that lack specificity and/or function poorly in cells where ATP levels are high. Molecules targeting the allosteric site in the inactive kinase conformation (type II inhibitors) provide an alternative for developing selective inhibitors that are physiologically active. By applying a rational design approach using a constrained amino-triazole scaffold predicted to stabilize kinases in the inactive state, we generated a series of selective type II inhibitors of PDGFRβ and B-RAF, important targets for pericyte recruitment and endothelial cell survival, respectively. These molecules were designed in silico and screened for antivascular activity in both cell-based models and a Tg(fli1-EGFP) zebrafish embryogenesis model. Dual inhibition of PDGFRβ and B-RAF cellular signaling demonstrated synergistic antiangiogenic activity in both zebrafish and murine models of angiogenesis, and a combination of previously characterized PDGFRβ and RAF inhibitors validated the synergy. Our lead compound was selected as an orally active molecule with favorable pharmacokinetic properties which demonstrated target inhibition in vivo leading to suppression of murine orthotopic tumors in both the kidney and pancreas.

New luminescence ages for the Galería Complex archaeological site: resolving chronological uncertainties on the acheulean record of the Sierra de Atapuerca, northern Spain.

The archaeological karstic infill site of Galería Complex, located within the Atapuerca system (Spain), has produced a large faunal and archaeological record (Homo sp. aff. heidelbergensis fossils and Mode II lithic artefacts) belonging to the Middle Pleistocene. Extended-range luminescence dating techniques, namely post-infrared infrared stimulated luminescence (pIR-IR) dating of K-feldspars and thermally transferred optically stimulated luminescence (TT-OSL) dating of individual quartz grains, were applied to fossil-bearing sediments at Galería. The luminescence dating results are in good agreement with published chronologies derived using alternative radiometric dating methods (i.e., ESR and U-series dating of bracketing speleothems and combined ESR/U-series dating of herbivore teeth), as well as biochronology and palaeoenvironmental reconstructions inferred from proxy records (e.g., pollen data). For the majority of samples dated, however, the new luminescence ages are significantly (∼50%) younger than previously published polymineral thermoluminescence (TL) chronologies, suggesting that the latter may have overestimated the true burial age of the Galería deposits. The luminescence ages obtained indicate that the top of the basal sterile sands (GIb) at Galería have an age of up to ∼370 thousand years (ka), while the lowermost sub-unit containing Mode II Acheulean lithics (base of unit GIIa) was deposited during MIS 9 (mean age = 313±14 ka; n = 4). The overlying units GIIb-GIV, which contain the richest archaeopalaeontological remains, were deposited during late MIS 8 or early MIS 7 (∼240 ka). Galería Complex may be correlative with other Middle Pleistocene sites from Atapuerca, such as Gran Dolina level TD10 and unit TE19 from Sima del Elefante, but the lowermost archaeological horizons are ∼100 ka younger than the hominin-bearing clay breccias at the Sima de los Huesos site. Our results suggest that both pIR-IR and single-grain TT-OSL dating are suitable for resolving Middle Pleistocene chronologies for the Sierra de Atapuerca karstic infill sequences.

Cultural innovation and megafauna interaction in the early settlement of arid Australia

Elucidating the material culture of early people in arid Australia and the nature of their environmental interactions is essential for understanding the adaptability of populations and the potential causes of megafaunal extinctions 50–40 thousand years ago (ka). Humans colonized the continent by 50 ka, but an apparent lack of cultural innovations compared to people in Europe and Africa has been deemed a barrier to early settlement in the extensive arid zone. Here we present evidence from Warratyi rock shelter in the southern interior that shows that humans occupied arid Australia by around 49 ka, 10 thousand years (kyr) earlier than previously reported. The site preserves the only reliably dated, stratified evidence of extinct Australian megafauna, including the giant marsupial Diprotodon optatum, alongside artefacts more than 46 kyr old. We also report on the earliest-known use of ochre in Australia and Southeast Asia (at or before 49–46 ka), gypsum pigment (40–33 ka), bone tools (40–38 ka), hafted tools (38–35 ka), and backed artefacts (30–24 ka), each up to 10 kyr older than any other known occurrence. Thus, our evidence shows that people not only settled in the arid interior within a few millennia of entering the continent, but also developed key technologies much earlier than previously recorded for Australia and Southeast Asia.

Holocene palaeofire records in a high-level, proximal valley-fill (Wilson Bog), Mount Lofty Ranges, South Australia

An elevated valley-fill peat bog (Wilson Bog) near Mount Lofty, South Australia, failed in November 2005 following a flooding event, and exposed representative sections of the sediment infill. Two distinct units were revealed: 2 m of coarse-grained, siliciclastic sand/gravel, overlain by 2 m of peat. A simple charcoal extraction technique based on floatation and skimming was developed to extract coarse charcoal from coarse-grained gravels to determine the palaeofire record at a proximal site of sedimentation. Optically stimulated luminescence (OSL) dating of basal sediments revealed a minimum age of deposition of 7.02 +0.50 —0.56 ka, while the oldest charcoal peak yielded a radiocarbon age of 6000—5740 cal. yr BP. The lower half of the siliciclastic unit contains three distinct charcoal peaks suggesting there were infrequent but intense fires associated with wetter conditions during the Holocene climatic optimum 8000—5000 years ago. The period from 4000 to 2000 cal. yr BP is characterised by more frequent charcoal peaks and higher background levels of charcoal, which is consistent with more regular but less intense fires during drier, cooler conditions. The sharp transition from siliciclastic sedimentation to peat formation began ~1200 cal. yr BP, which may relate to a return to wetter conditions. However, fire frequency appears to have increased in this time suggesting augmentation by anthropogenic or ENSO-related factors. Charcoal-rich layers in the siliciclastic unit are associated with poorly sorted, bimodal sediments with high proportions of clay, silt and gravel, which supports the hypothesis that there is an association between past fire events and rapid, coarse-grained, post-fire aggradation. By analogy with active colluvial aggradation following recent fires at nearby Mount Bold, it is evident that fire plays a significant role in hillslope destabilization and subsequent sediment movement, leading to rapid valley-fill aggradation — a chain of events to which we apply the term ‘pyrocolluviation’.