Earliest known crown-group salamanders

Salamanders are a model system for studying the rates and patterns of the evolution of new anatomical structures. Recent discoveries of abundant Late Jurassic and Early Cretaceous salamanders are helping to address these issues. Here we report the discovery of well-preserved Middle Jurassic salamanders from China, which constitutes the earliest known record of crown-group urodeles (living salamanders and their closest relatives). The new specimens are from the volcanic deposits of the Jiulongshan Formation (Bathonian), Inner Mongolia, China, and represent basal members of the Cryptobranchidae, a family that includes the endangered Asian giant salamander (Andrias) and the North American hellbender (Cryptobranchus). These fossils document a Mesozoic record of the Cryptobranchidae, predating the previous record of the group by some 100 million years. This discovery provides evidence to support the hypothesis that the divergence of the Cryptobranchidae from the Hynobiidae had taken place in Asia before the Middle Jurassic period.     

Earliest known proboscidean from early Eocene of north-west Africa

The earliest known proboscidean remains have now been found at a new early Eocene locality at Brezina in southern Algeria (El Kohol). These new finds, represented by complete skulls and postcranial material, show several unexpected derived characters shared with the modern representatives of the Elephantoidea and the Deinotheriidae, suggesting close phylogenetic affinities and demonstrating also the great antiquity of the differentiation of modern proboscideans in Africa. These remains have been dated by associated charophyte flora and vertebrate remains which constitute the oldest known vertebrate community from the African Eocene.     

Earliest Homo.

The origin of our own genus, Homo, has been tentatively correlated with worldwide climatic cooling documented at about 2.4 Myr (million years). It has also been conjectured that members of Homo made the first stone tools, currently dated at 2.6-2.4 Myr. But fossil specimens clearly attributable to Homo before about 1.9 Myr have been lacking. In 1967 a fossil hominoid temporal bone (KNM-BC1) from the Chemeron Formation of Kenya was described as family Hominidae gen. et sp. indet. Although a surface find, its provenance within site JM85 (BPRP site K002) was established and a stratigraphic section provided indicating the specimen's position. This evidence has been affirmed but the exact age of the fossil was never determined, and the absence of suitable comparative hominid material has precluded a more definitive taxonomic assignment. Here we present 40Ar/39Ar age determinations on material from the hominid site indicating an age of 2.4 Myr. In addition, comparative studies allow us to assign KNM-BC1 to the genus Homo, making it the earliest securely known fossil of our own genus found so far.     

Earliest presence of humans in northeast Asia

The timing of the earliest habitation and oldest stone technologies in different regions of the world remains a contentious topic in the study of human evolution. Here we contribute to this debate with detailed magnetostratigraphic results on two exposed parallel sections of lacustrine sediments at Xiaochangliang in the Nihewan Basin, north China; these results place stringent controls on the age of Palaeolithic stone artifacts that were originally reported over two decades ago. Our palaeomagnetic findings indicate that the artifact layer resides in a reverse polarity magnetozone bounded by the Olduvai and Jaramillo subchrons. Coupled with an estimated rate of sedimentation, these findings constrain the layer's age to roughly 1.36 million years ago. This result represents the age of the oldest known stone assemblage comprising recognizable types of Palaeolithic tool in east Asia, and the earliest definite occupation in this region as far north as 40 degrees N.     

N.维纳在清华大学与中国最早计算机研究

20世纪30年代,清华大学邀请美国麻省理工学院N.维纳教授来华任客座教授.其前后有关的原始信件及资料,证明了他在清华大学与李郁荣等人开创了中国模拟计算机的研究.     

The earliest known fully quadrupedal sirenian.

Modern seacows (manatees and dugongs; Mammalia, Sirenia) are completely aquatic, with flipperlike forelimbs and no hindlimbs. Here I describe Eocene fossils from Jamaica that represent nearly the entire skeleton of a new genus and species of sirenian--the most primitive for which extensive postcranial remains are known. This animal was fully capable of locomotion on land, with four well-developed legs, a multivertebral sacrum, and a strong sacroiliac articulation that could support the weight of the body out of water as in land mammals. Aquatic adaptations show, however, that it probably spent most of its time in the water. Its intermediate form thus illustrates the evolutionary transition between terrestrial and aquatic life. Similar to contemporary primitive cetaceans, it probably swam by spinal extension with simultaneous pelvic paddling, unlike later sirenians and cetaceans, which lost the hindlimbs and enlarged the tail to serve as the main propulsive organ. Together with fossils of later sirenians elsewhere in the world, these new specimens document one of the most marked examples of morphological evolution in the vertebrate fossil record.     

Materials science. The hardest known oxide

A material as hard as diamond or cubic boron nitride has yet to be identified, but here we report the discovery of a cotunnite-structured titanium oxide which represents the hardest oxide known. This is a new polymorph of titanium dioxide, where titanium is nine-coordinated to oxygen in the cotunnite (PbCl2) structure. The phase is synthesized at pressures above 60 gigapascals (GPa) and temperatures above 1,000 K and is one of the least compressible and hardest polycrystalline materials to be described.     

The spatial arrangement of cones in the primate fovea.

The retinae of Old World primates contain three classes of light-sensitive cone, which exhibit peak absorption in different spectral regions. But how are the different types of cone arranged in the hexagonal mosaic of the fovea? This question has often been answered with artists' impressions, but never with direct measurements. Staining for antibodies specific to the short-wave photopigment has revealed a sparse, semiregular array of cones; but nothing is known about the arrangement of the more numerous long- and middle-wave cones. Are they randomly distributed, with chance aggregations of one type, as Hartridge postulated in these columns nearly 50 years ago? Or do they exhibit a regular alteration, recalling the systematic mosaics seen in some non-mammalian species? Or, conversely, is there positive clumping of particular cone types, as might be expected if local patches of cones were descended from a single precursor cell? We have made direct microspectrophotometric measurements of patches of foveal retina from Old World monkeys, and report here that the distribution of long- and middle-wave cones is locally random. These two cone types are present in almost equal numbers, and not in the ratio of 2:1 that has been postulated for the human fovea.     

Visual categorization shapes feature selectivity in the primate temporal cortex.

The way that we perceive and interact with objects depends on our previous experience with them. For example, a bird expert is more likely to recognize a bird as a sparrow, a sandpiper or a cockatiel than a non-expert. Neurons in the inferior temporal cortex have been shown to be important in the representation of visual objects; however, it is unknown which object features are represented and how these representations are affected by categorization training. Here we show that feature selectivity in the macaque inferior temporal cortex is shaped by categorization of objects on the basis of their visual features. Specifically, we recorded from single neurons while monkeys performed a categorization task with two sets of parametric stimuli. Each stimulus set consisted of four varying features, but only two of the four were important for the categorization task (diagnostic features). We found enhanced neuronal representation of the diagnostic features relative to the non-diagnostic ones. These findings demonstrate that stimulus features important for categorization are instantiated in the activity of single units (neurons) in the primate inferior temporal cortex.     

自由与规范:中国早期电影的放映活动

早期电影研究的一个主要的学术关切是相关的文化语境与概念,而不是电影本身.比如,在中国早期电影的研究中,就需要关心"运动"(motion)的概念和经验,藉此可以研究空间、视觉和主体性之间的关系,并揭示传统和现代文化环境之间的紧张与对话.