Thrombolite fabrics and origins: Influences of diverse microbial and metazoan processes on Cambrian thrombolite variability in the Great Basin,California and Nevada

Thrombolites are a common component of carbonate buildups throughout the Phanerozoic. Although they are usually described as microbialites with an internally clotted texture, a wide range of thrombolite textures have been observed and attributed to diverse processes, leading to difficulty interpreting thrombolites as a group. Interpreting thrombolitic textures in terms of ancient ecosystems requires understanding of diverse processes, specifically those due to microbial growth and metazoan activity. Many of these processes are reflected in thrombolites in the Cambrian Carrara, Bonanza King, Highland Peak and Nopah formations, Great Basin, California, USA; they comprise eight thrombolite classes based on variable arrangements and combinations of depositional and diagenetic components. Four thrombolite classes (hemispherical microdigitate, bushy, coalescent columnar and massive fenestrated) contain distinct mesoscale microbial growth structures that can be distinguished from surrounding detrital sediments and diagenetic features. By contrast, mottled thrombolites have mesostructures that dominantly reflect post‐depositional processes, including bioturbation. Mottled thrombolites are not bioturbated stromatolites, but rather formed from disruption of an originally clotted growth structure. Three thrombolite classes (arborescent digitate, amoeboid and massive) contain more cryptic textures. All eight of the thrombolite classes in this study formed in similar Cambrian depositional environments (marine passive margin). Overall, this suite of thrombolites demonstrates that thrombolites are diverse, in both internal fabrics and origin, and that clotted and patchy microbialite fabrics form from a range of processes. The diversity of textures and their origins demonstrate that thrombolites should not be used to interpret a particular ecological, evolutionary or environmental shift without first identifying the microbial growth structure and distinguishing it from other depositional, post‐depositional and diagenetic components. Furthermore, thrombolites are fundamentally different from stromatolites and dendrolites in which the laminae and dendroids reflect a primary growth structure, because clotted textures in thrombolites do not always reflect a primary microbial growth structure.     

Parasitic barnacles (Cirripedia: Rhizocephala) from New Zealand off‐shore waters

Nine genera and species of rhizocephalans were recorded from the off‐shore waters around New Zealand. Mitochondrial and nuclear gene sequences were used to examine base differences between the European and New Zealand species of Parthenopea. Serial sections to study the internal structures of the reproductive organs were made for the genera Thylacoplethus and Thompsonia. Two species, Parthenopea australis n. sp. and Thylacoplethus novaezealandiae n. sp. are new to science and described in detail. Parthenopea australis n. sp. is the first rhizocephalan species recorded from the vicinity of active cold seeps. Three rhizocephalans could not be identified as they were parasitised by hyperparasitic cryptoniscine isopods. The decapodhost species comprised the taxa Paguridae, Lithodidae, Galatheidae, Chirostylidae, and Callianassidae.     

140OΜα前的后生动物实体化石?

本文首次报道了在我国豫西晚前寒武系白草坪组中发现的一种可能的蠕虫状后生动物实体化石:Ruyangia Cylindrica Hu et Meng,1989。化石产于砂岩表面浪成波痕之波谷中,圆筒状,已压扁,中空,可见长度4.5～9.5cm,直径4mm左右,虫体外壁具体环,环背间距1.5～2mm,虫体一端较大,具平行纵向边缘的纵纹,可能为头部;另一端渐尖,可能为尾部。与该实体化石伴生的有大量遗迹化石。已知白草坪组的时代超过1400Ma,因此,该实体化石的发现对研究地球上后生动物起源与早期演化等具重要意义。     

Extinctions, Morphological Gaps, Major Transitions, Stem Groups, and the Origin of Major Clades, with a Focus on Early Animals

Systematic extinctions can leave major morphological gaps between living crown-group clades. Such morphological gaps would be perceived, from a neontological point of view, as major evolutionary transitions. In order to fill these morphological gaps and to map the evolutionary steps toward major evolutionary transitions, we need to integrate extinct stem-group taxa in phylogenetic studies. However, the recognition of stem group has not been widely adopted in the study of early animal fossils, despite that all fossils are stem groups at one level or another. Part of the difficulty is that stem groups may not have all features that collectively diagnose the respective crown group, and they can have unique (autapomorphic) features, making them tantalizingly similar to and frustratingly different from the crown group (e.g., stem-group eukaryotes can be prokaryotic and stem-group animals can be protistan). The need to embrace stem groups and to implement the PhyloCode, in order to achieve phylogenetic clarity and to offer key paleontological insights into the origin and early animal evolution, is illustrated in debates on several controversial Ediacaran and Cambrian fossils.     

晚震旦世陡山沱期后生生物群的古生态环境探讨

早期后生生物群是当前古生物学研究热点之一。我国上扬子区的庙河生物群和瓮安生物群是震旦纪的重要生物群,而生物群是怎样繁盛和埋藏保存是研究早期后生生物群的一个重要方面。作者研究认为翁安生物群是由于洋流上升提供了大量的ＳｉＯ２和Ｐ２Ｏ５等养分,使生物在台地边缘大规模繁盛,其海水由于富ＳｉＯ２和Ｐ２Ｏ５所引起强烈的磷酸岩化及硅化作用,使大量的生物尸体被快速矿化,形成具有抗水动力强的骨架,避免水动力和氧化作     

豫西前寒武纪汝阳群遗迹化石

本文研究的遗迹化石：Ｒｕｙａｎｇｉｃｈｎｕｓ ｌｏｙｕｅｎｓｉｓ ｉｃｈｎｏｇｅｎ，ｅｔ ｉｃｈｎｏｓｐ．ｎｏｖ．，Ｔｏｒｒｏｗａｎｇｅａ ｒｏｓｅｉ ｗｅｂｂｙ，Ｃｈａｎｇｃｈｅｎｇｉａ ｉｃｈｎｏｓｐ．，Ｓｑｕａｍｏｄｉｃｔ ｙｏｎ（？）ｉｃｈｎｏｓｐ．等发现于河南西部鲁山县和汝阳县的汝阳群云梦山组和北大尖组。根据同位素年龄值，微古植物和叠层石资料，产遗迹化石的汝阳群应相当于中元古代，可以和蓟     

晚震旦世陡山沱期后生生物群的古生态环境探讨

早期后生生物群是当前古生物学研究热点之一。我国上扬子区的庙河生物群和瓮安生物群是震旦纪的重要生物群,而生物群是怎样繁盛和埋藏保存是研究早期后生生物群的一个重要方面。作者研究认为瓮安生物群是由于洋流上升提供了大量的ＳｉＯ２ 和Ｐ２Ｏ５ 等养分,使生物在台地边缘大规模繁盛,其海水由于富ＳｉＯ２ 和Ｐ２Ｏ５ 所引起强烈的磷酸岩化及硅化作用,使大量的生物尸体被快速矿化,形成具有抗水动力强的骨架,避免水动力和氧化作用的破坏,因此,矿化作用是生物体保存为化石的另一个重要因素。最后,提出上扬子区陡山沱期为有利于生物群繁盛和保存区域     

热带浅水湖泊后生浮游动物群落结构对生态修复的响应

热带浅水湖泊后生浮游动物群落以轮虫和小型枝角类为主,往往缺乏大型浮游动物,其影响因子还存在争议,因此通过减少鱼类,提高大型后生浮游动物密度,从而增强对浮游植物的下行控制、修复热带富营养化湖泊的方法受到质疑.暨大南湖位于广州暨南大学校园内,是热带富营养化浅水湖泊,于2014年1—2月实施以鱼类去除和水生植被重建为主的生态系统修复工程,以期改善水质.通过对南湖修复前后水质、后生浮游动物以及修复后鱼类群落的调查分析,研究了后生浮游动物群落对修复的响应.结果表明:与修复前相比,总氮、总磷和叶绿素a浓度显著降低,透明度显著上升.枝角类丰度和生物量显著增加,修复后初期出现较高密度的大型枝角类蚤状溞(Daphnia pulex),桡足类丰度和生物量没有显著变化,轮虫丰度下降而生物量上升;后生浮游动物体长和生物多样性显著增加.随着鱼类密度的增加,蚤状溞丰度快速降低,后期鱼类减少后蚤状溞丰度又有所升高.因此,本研究显示鱼类是控制热带浅水湖泊大型浮游动物种群的主要因素,由于控制鱼类密度以维持较高大型浮游动物密度较为困难,因此单纯生物操纵在热带浅水湖泊修复中难以取得显著效果.