RESUMEN
Owing to the lack of temporally well-constrained Ediacaran fossil localities containing overlapping biotic assemblages, it has remained uncertain if the latest Ediacaran (ca 550-541 Ma) assemblages reflect systematic biological turnover or environmental, taphonomic or biogeographic biases. Here, we report new latest Ediacaran fossil discoveries from the lower member of the Wood Canyon Formation in Nye County, Nevada, including the first figured reports of erniettomorphs, Gaojiashania, Conotubus and other problematic fossils. The fossils are spectacularly preserved in three taphonomic windows and occur in greater than 11 stratigraphic horizons, all of which are below the first appearance of Treptichnus pedum and the nadir of a large negative δ13C excursion that is a chemostratigraphic marker of the Ediacaran-Cambrian boundary. The co-occurrence of morphologically diverse tubular fossils and erniettomorphs in Nevada provides a biostratigraphic link among latest Ediacaran fossil localities globally. Integrated with a new report of Gaojiashania from Namibia, previous fossil reports and existing age constraints, these finds demonstrate a distinctive late Ediacaran fossil assemblage comprising at least two groups of macroscopic organisms with dissimilar body plans that ecologically and temporally overlapped for at least 6 Myr at the close of the Ediacaran Period. This cosmopolitan biotic assemblage disappeared from the fossil record at the end of the Ediacaran Period, prior to the Cambrian radiation.
Asunto(s)
Evolución Biológica , Fósiles , Namibia , Nevada , PaleontologíaRESUMEN
Synthetic materials currently used for arterial grafts can provoke serious complications such as infection, rejection, and incomplete reendothelialization. Porcine small intestinal submucosa (SIS) allografts (homografts) may not share these disadvantages yet still may provide an effective graft alternative. This study was designed to provide additional information concerning the performance of this material when used as an allo-patch graft. A porcine model was selected to enable hemodynamic comparisons to the adult human physiology. Slaughterhouse small intestine was used to prepare the SIS graft material. A well-vascularized section ofjejunum was resected, rinsed, and maintained in 0.9% NaCl solution containing 10% gentamicin. The graft was prepared by removing the serosal layer, inverting the material, and discarding the mucosal surface in a similar manner. The remaining submucosa and stratum compactum constituted the graft material and was subdivided into sizes from 1.5 to 3.0 cm2 tacked to foil for manageability, and was returned to the gentamicin solution. The surgery was initiated with a femoral arterial line in the anesthetized swine, followed by isolation and preparation of the infrarenal aorta for grafting. Cross-clamps were applied and a 1.0 x 1.5-cm section of aortic wall was resected. Two sides of allograft were freed from the foil and sewn into the aorta. Then the remaining sides were removed from the foil and final graft placement was completed. The graft was harvested at postoperative day 28 and presented for microscopic examination. Results confirmed that reendothelialization with neovascularization had occurred during this interval.