中国北方上中新统的早期玛姆象属(Mammut)及其在玛姆象科(Mammutidae)分化和演化中的意义

玛姆象属是长鼻类玛姆象科这一重要类群的最终成员.虽然这一属在上新世的欧亚大陆和更新世的北美大陆广泛分布,它早期的进化历史却鲜为人知.报道了中国北方上中新统发现的斜脊玛姆象(相似种)(Mammut cf.M.obliquelophus)的新材料,包括一个几乎完整的幼年头骨,这些材料显示了玛姆象科的许多原始特征,因此很好地解释了玛姆象属形态特征的形成过程.斜脊玛姆象(相似种)具有强烈向两侧扩展的枕部,在门齿窝的基部具有收缩,这些特征与莫罗托始轭齿象(Eozygodon morotoensis)和广河豕脊齿象(Choerolophodon guangheensis)均具有相似性,后两者分别为玛姆象科与豕脊齿象科的早期代表.因此,玛姆象科与豕脊齿象科(Choerolophodontidae)具有近的亲缘关系,二者同位于象形类(Elephantimorpha)系统发育中的基部.支序分析支持了这一结论.     

The Oldest Cranium of <Emphasis Type="Italic">Sinomastodon</Emphasis> (Proboscidea,Gomphotheriidae), Discovered in the Uppermost Miocene of Southwestern China: Implications for the Origin and Migration of This Taxon

The origin of the Old World brevirostrine gomphotheriid taxon Sinomastodon has been debated intensively. The discovery of the oldest known Sinomastodon cranium, reported herein, supports its endemic origin and contradicts the prevalent theory of its North America origin. The new cranium was discovered from the Shuitangba locality, southwestern China, and is dated at about 6.5–6.0 Ma, corresponding to the latest Miocene. The new specimen shows distinct characters from the other species of Sinomastodon and was therefore named Sinomastodon praeintermedius, sp. nov. Newly discovered, isolated Sinomastodon-like teeth from the upper Miocene to the lower Pleistocene of southwestern China and Southeast Asia indicate a long evolution of Sinomastodon endemically. Remains of this species are frequently accompanied by those of stegodontid species. These two groups may have had a similar migration route, invading northern China and Japan during the latest Miocene, and retreating or becoming extinct from the Palearctic realm by the end of the Pliocene. The migrations of proboscideans may have been sparked by major paleoenviromental changes, i.e., the strengthened summer monsoon beginning in the late Miocene (~7–8 Ma) and global cooling due to the expansion of ice sheets from the middle Pliocene to the early Pleistocene. The new finding reveals a close relationship of the early Pliocene fauna of northern China and the latest Miocene fauna of southwestern China, and thus provides novel insight into the origin and components of Pliocene fauna in northern China.     

Effects of elevated temperature on growth, respiratory-deficient mutation, respiratory activity, and ethanol production in yeast

Some mesophilic yeasts and a thermotolerant strain of Saccharomyces cerevisiae were found to grow at 40 degrees C in complex media containing 1% yeast extract when an inoculum of 10(6) or more cells.mL-1 was used. Yeast extract (6%) permitted Saccharomyces cerevisiae to grow at 40 degrees C even with a smaller inoculum size (10(5) cells.mL-1). The fraction of respiratory-deficient (petite) mutants in 40 degrees C grown culture was less than 10% except for the thermotolerant strain, which showed greatly increased levels depending on culture conditions. Seven of eight yeast strains exhibited extremely reduced cytochrome oxidase activity when grown at 40 degrees C irrespective of the frequency of the petite mutation. In contrast, the accumulation of ethanol in the medium and the ethanol-producing activity of the cells were not affected by growth at 40 degrees C.