The Early Cambrian Haikouichthys and Haikouella have been claimed to be related to contribute in an important way to our understanding of vertebrate origin, but there have been heated debates about how exactly they are to be interpreted. New discoveries of numerous speci-mens of Haikouichthys not only confirm the identity of pre-viously described structures such as the dorsal and the ven-tral fins, and chevron-shaped myomeres, but also reveal many new important characteristics, including sensory or-gans of the head (e.g. large eyes), and a prominent notochord with differentiated vertebral elements. This 揻irst fish?ap-pears, however, to retain primitive reproductive features of acraniates, suggesting that it is a stem-group craniates. A new order (Myllokunmingiida) and a new family (Myllo-kunmingiidae) are erected, and a new species, Zhongjianich-thys rostratus (gen. et sp. nov.), is described herein. Over 1400 newly-discovered specimens of Haikouella provide a wealth of anatomical information on this organism. It differs from chordates in many organs and organ systems, including the skin, muscles, respiratory, circulatory and nervous sys-tems. In contrast, its body-design resembles that of vetuli-colians, and the presence of a 搕ransitional?nervous system with both dorsal and ventral nerve cords suggests an affinity with living hemichordates. On the basis of these and other recent findings of fossil deuterostomes, a five-step hypothesis for vertebrate origin is proposed, intended to bridge the long- standing gap between protostomes and vertebrates. Four of the five steps accord with established ideas current in modern evolutionary zoology. Evidence for the first step is obtainable only from fossils, and specifically from fossils found from South China, hence the crucial importance of S. China sites for our understanding of early vertebrate origins and evolution. Accordingly, South China is suggested as the oldest-known birthplace of the whole vertebrates.
SHU Degan Early Life Institute & Department of Geology, Northwest University, Xi抋n, 710069, China
Cotton fiber is a highly elongated and thickened single cell that produces large quantities of cellulose,which is synthesized and assembled into cell wall microfibrils by the cellulose synthase complex(CSC).In this study,we report that in cotton(Gossypium hirsutum)fibers harvested during secondary cell wall(SCW)synthesis,GhCesA 4,7,and 8 assembled into heteromers in a previously uncharacterized 36-mer-like cellulose synthase supercomplex(CSS).This super CSC was observed in samples prepared using cotton fiber cells harvested during the SCW synthesis period but not from cotton stem tissue or any samples obtained from Arabidopsis.Knock-out of any of GhCesA 4,7,and 8 resulted in the disappearance of the CSS and the production of fiber cells with no SCW thickening.Cotton fiber CSS showed significantly higher enzyme activity than samples prepared from knock-out cotton lines.We found that the microfibrils from the SCW of wild-type cotton fibers may contain 72 glucan chains in a bundle,unlike other plant materials studied.GhCesA4,7,and 8 restored both the dwarf and reduced vascular bundle phenotypes of their orthologous Arabidopsis mutants,potentially by reforming the CSC hexamers.Genetic complementation was not observed when non-orthologous CesA genes were used,indicating that each of the three subunits is indispensable for CSC formation and for full cellulose synthase function.Characterization of cotton CSS will increase our understanding of the regulation of SCW biosynthesis.
The efforts of labor-intensive collecting in the Early Cambrian Chengjiang deposits in eastern Yunnan Province, China led to the discovery of many horizons containing exceptionally well preserved soft-bodied fossil concentrations, many of which can be assigned to either monospecific concentrations or paucispecific concentrations. The features of these fossil concentrations support the hypothesis that frequent storm events producing tempestites mainly contributed to the preservation of abundant soft- bodied fossils in the Chengjiang deposits, and indi- cate that the balance of the ecological web in this region was probably frequently destroyed or upset by such storm events during that geological time. Ani- mals in a fossil assemblage in such fossil concentra- tions probably occupied similar ecological biotopes.
HAN JianSHU DeganZHANG ZhifeiLIU JianniZHANG XingliangYAO Yang
The Chengjiang Lagerstatte has been celebrated for prolific soft-bodied fossils. Based on specimens recently excavated in the Chengjiang Lagerstatte by the Early Life Institute, Northwest University, Diandongia pista Rong, 1974, is directly revealed to be a pediculate brachiopod, assigned to the Family Botsfordiidae, as is further confirmed by the exceptionally preserved vascular system including dorsal and ventral mantle canals. These specimens described herein exhibit some peculiarities, notably the extremely thin and long pedicles, which suggest that Diandongia is epifaunal rather than burrowing brachiopod. A study of this group of animals indicates that they may be vital to understand the relationship between the lingulids and the remaining brachiopods, and the character evolution of the early Cambrian brachiopods.
ZHANG Zhifei, HAN Jian, ZHANG Xingliang, LIU Jianni and SHU DeganEarly Life Institute and Key Laboratory for Continental Dynamics of the Ministry of Education,Northwest University, Xi’an, Shaanxi 710069
