Catálogo de publicaciones - revistas

<jats:p>What drives scientific discovery, and how can we make it happen more effectively?</jats:p>

<jats:p>Progress in defining a signaling pathway that controls mammalian life span raises the possibility of discovering treatments for aging-related diseases.</jats:p>

<jats:p>Rising atmospheric concentrations of nitrous oxide are contributing to global warming and stratospheric ozone destruction.</jats:p>

<jats:p>A mitochondrial protein linked to seizures exchanges calcium and hydrogen ions, controlling cell respiration and calcium signaling.</jats:p>

<jats:p> In this special video, <jats:italic>Science</jats:italic> presents <jats:italic>Ardipithecus ramidus</jats:italic> --the most detailed picture of early hominid life. </jats:p>

<jats:p> Hominid fossils predating the emergence of <jats:italic>Australopithecus</jats:italic> have been sparse and fragmentary. The evolution of our lineage after the last common ancestor we shared with chimpanzees has therefore remained unclear. <jats:italic>Ardipithecus ramidus</jats:italic> , recovered in ecologically and temporally resolved contexts in Ethiopia’s Afar Rift, now illuminates earlier hominid paleobiology and aspects of extant African ape evolution. More than 110 specimens recovered from 4.4-million-year-old sediments include a partial skeleton with much of the skull, hands, feet, limbs, and pelvis. This hominid combined arboreal palmigrade clambering and careful climbing with a form of terrestrial bipedality more primitive than that of <jats:italic>Australopithecus</jats:italic> . <jats:italic>Ar. ramidus</jats:italic> had a reduced canine/premolar complex and a little-derived cranial morphology and consumed a predominantly C <jats:sub>3</jats:sub> plant–based diet (plants using the C <jats:sub>3</jats:sub> photosynthetic pathway). Its ecological habitat appears to have been largely woodland-focused. <jats:italic>Ar. ramidus</jats:italic> lacks any characters typical of suspension, vertical climbing, or knuckle-walking. <jats:italic>Ar. ramidus</jats:italic> indicates that despite the genetic similarities of living humans and chimpanzees, the ancestor we last shared probably differed substantially from any extant African ape. Hominids and extant African apes have each become highly specialized through very different evolutionary pathways. This evidence also illuminates the origins of orthogrady, bipedality, ecology, diet, and social behavior in earliest Hominidae and helps to define the basal hominid adaptation, thereby accentuating the derived nature of <jats:italic>Australopithecus</jats:italic> . </jats:p>

<jats:p> Sediments containing <jats:italic>Ardipithecus ramidus</jats:italic> were deposited 4.4 million years ago on an alluvial floodplain in Ethiopia’s western Afar rift. The Lower Aramis Member hominid-bearing unit, now exposed across a &gt;9-kilometer structural arc, is sandwiched between two volcanic tuffs that have nearly identical <jats:sup>40</jats:sup> Ar/ <jats:sup>39</jats:sup> Ar ages. Geological data presented here, along with floral, invertebrate, and vertebrate paleontological and taphonomic evidence associated with the hominids, suggest that they occupied a wooded biotope over the western three-fourths of the paleotransect. Phytoliths and oxygen and carbon stable isotopes of pedogenic carbonates provide evidence of humid cool woodlands with a grassy substrate. </jats:p>

<jats:p> Thousands of vertebrate specimens were systematically collected from the stratigraphic interval containing <jats:italic>Ardipithecus ramidus</jats:italic> . The carcasses of larger mammals were heavily ravaged by carnivores. Nearly 10,000 small-mammal remains appear to be derived primarily from decomposed owl pellets. The rich avifauna includes at least 29 species, mostly nonaquatic forms. Modern analogs of the most abundant birds and of a variety of rodents are associated with mesic woodland environments distant from large water bodies. These findings support inferences from associated geological, isotopic, invertebrate, and large-vertebrate assemblages. The combined results suggest that <jats:italic>Ar. ramidus</jats:italic> occupied a wooded Pliocene habitat. </jats:p>

<jats:p> A diverse assemblage of large mammals is spatially and stratigraphically associated with <jats:italic>Ardipithecus ramidus</jats:italic> at Aramis. The most common species are tragelaphine antelope and colobine monkeys. Analyses of their postcranial remains situate them in a closed habitat. Assessment of dental mesowear, microwear, and stable isotopes from these and a wider range of abundant associated larger mammals indicates that the local habitat at Aramis was predominantly woodland. The <jats:italic>Ar. ramidus</jats:italic> enamel isotope values indicate a minimal C <jats:sub>4</jats:sub> vegetation component in its diet (plants using the C <jats:sub>4</jats:sub> photosynthetic pathway), which is consistent with predominantly forest/woodland feeding. Although the Early Pliocene Afar included a range of environments, and the local environment at Aramis and its vicinity ranged from forests to wooded grasslands, the integration of available physical and biological evidence establishes <jats:italic>Ar. ramidus</jats:italic> as a denizen of the closed habitats along this continuum. </jats:p>