中国三叠纪海生爬行动物化石研究的回顾与进展

中国三叠纪海生爬行动物化石研究始于20世纪50年代,近10年来取得了重要的进展。此类化石在华南分布广泛,已见于多个省区的十余处地点,涉及自下三叠统奥伦尼克阶至上三叠统诺利阶的至少7个层位,并显示出由东向西产出层位逐渐升高的趋势。我国的三叠纪海生爬行动物化石门类齐全,属种丰富,已知类群包括鱼龙类、海龙类、檐齿龙类、始鳍龙类、原龙类、初龙类和湖北鳄类,显示出典型的西特提斯动物群特征,同时也体现了与东太平洋动物群的某些联系,以及一定的地方色彩。这些化石为研究三叠纪海生爬行动物各个类群的起源、演化和绝灭以及海洋环境的变迁提供了新的材料。     

中国三叠纪海生爬行类综述

三叠纪海生爬行类化石广泛分布于中国南方的安徽、湖北、贵州、云南、广西和西藏。它们不仅包括有世界性分布的鱼龙类、鳍龙类、海龙类、原龙类等,而且还有仅出现于扬子海区的湖北鳄类。简单回顾了中国三叠纪海生爬行类的研究历史。根据化石的地史分布确认了自早三叠世晚期至晚三叠世早期的7个海生爬行类组合带。它们是奥伦尼克期的 Chaohu- saurus-Keichousaurus-Hupehsuchus 组合带,安尼期的 Chinchenia-Sanchiaosaurus 组合带和 Dino- cephalosaurus-Mixosaurus 组合带,拉丁期的 Dingxiaosaurus 带和 Keichousaurus-Nothosaurus 组合带,卡尼期的 Anshunsaurus-Qianichthyosaurus-Sinocyamodus 组合带和诺利期的 Himalayasaurus 带。对化石的古地理环境分析表明,中国早三叠世晚期的海生爬行类主要分布于扬子海区东部(安徽、湖北)的浅海开阔台地和局限海台地。中三叠世由于东部地区的抬升,鱼龙类和鳍龙类向西扩散,在扬子区西部(贵州、云南)辐射发展,在拉丁期达到个体数量和种类的高峰。晚三叠世卡尼期动物的数量依然很多,个体有增大的趋向,但高级分类阶元的数量减少,它们埋藏于海水相对较深的浊积岩相中。晚三叠世诺利期的化石发现于西藏的定日和聂拉木,这是中国惟一属于冈瓦那特提斯区的三叠纪海生爬行类组合带,仅含大型的鱼龙类。受动物的生存环境和埋藏条件的影响,中国三叠纪海生爬行类化石记录并不完整。目前尚有相当数量的化石未经研究,已记述的化石也需要在研究程度上进一步深化。     

浙江和江西二叠/三叠系界线层上下的辐鳍鱼类化石与鱼类的绝灭、复苏和辐射

记述了浙江长兴县煤山剖面、江西修水县四都乡东岭剖面和信丰县铁石口镇铁石口剖面二叠/三叠系界线层上下的辐鳍鱼类6个类别的微体化石,包含2新属2新种,它们是:赵氏浙江鱼(Zhejiangichthys zhaoi gen.et sp.nov.)和小齿葆青鱼(Baoqingichthys microdontus gen.et sp.nov.)。这是包括全球二叠/三叠系界线层型剖面和点位(GSSP)在内的全球二叠/三叠系界线层上下辐鳍鱼类微体化石序列的首次报道。在总结煤山剖面已记述的鱼类大化石和微体化石资料的基础上,分析了长兴煤山剖面二叠纪末鱼类的集群绝灭。绝灭发生得很晚,持续的时间很短,规模也很大,绝灭率高达93%。讨论了华南二叠/三叠系之交大绝灭后鱼类的复苏和辐射,认为鱼类和牙形类一样都是大绝灭后在三叠纪最早复苏的类别,最早复苏的鱼类为裂齿鱼类;鱼类从绝灭期到辐射期仅用了1.3 Ma到4 Ma,从地质时间考虑,大绝灭后鱼类的复苏和辐射是相当快的。华南早三叠世以裂齿鱼类的张氏鱼(Zhangina)和软骨鱼类的弓鲛(Hybodus)为代表的组合替代了晚二叠世以古鳕类的中华扁体鱼(sinoplatysomys)和软骨鱼类的中华尖齿鲨(Sinacrodus)为代表的组合。华南晚二叠世海相地层产出的辐鳍鱼类和软骨鱼类的一些土著属与产于特提斯区三叠纪的一些属非常相近,表明华南下扬子区很可能是后来繁盛于特提斯区的三叠纪鱼类的发源地。     

论广西武鸣三叠纪海生爬行动物东方广西龙(鳍龙类)的时代

广西武鸣产出广西地区迄今唯一一件三叠纪海生爬行动物化石——东方广西龙(Kwangsisaurus orientalis)。受限于20世纪50年代研究条件,有关该化石产出地点、地层层位和时代信息一直比较模糊,对后人阐述中国三叠纪海生爬行动物演化过程及探究鳍龙类在华南的古地理迁移历史造成了一定阻碍。本文从岩石地层学和生物地层学入手,结合高精度同位素年代学定年结果,对武鸣地区早、中三叠世地层进行了综合分析,着重研究了含东方广西龙地层的岩性组合、生物群面貌及地层时代。东方广西龙产于板纳组薄层泥晶灰岩中,伴生有丰富的菊石化石,所属地层时代为中三叠世安尼期。对含东方广西龙地层上部层状凝灰岩中具有岩浆韵律的锆石进行了SIMS原位U-Pb年代学测试,获得了(244.2±0.7)Ma的绝对年龄值,时代相当于安尼期中晚期。东方广西龙时代的厘定排除了鳍龙类早三叠纪世晚期在下扬子区和右江盆地同时出现的原有结论,同时同位素年代学新证据证实广西武鸣海生爬行动物化石与贵州盘县海生爬行动物群基本同期,表明了鳍龙类在华南东部起源后在三叠纪中期向西南地区辐射扩散范围的广阔性和适应环境的多样性。     

湘西早志留世溶溪组无颌类的发现及其意义

本文记述了在湖南西部早志留世 Llandovery 期溶溪组发现的多鳃鱼目—新科——大庸鱼科 (Dayongaspidae fam. nov), 其标本代表了中国迄今为止地质时代最早的海生早期脊椎动物化石,并进而论证了中国的盔甲鱼类发生在近岸浅海地区,而不是大陆淡水盆地,其时代为前早志留世.扬子区是这类无颌类的发源地.     

安徽含山早志留世晚期陈夏村组的苔藓动物化石

本文首次报道了我国下扬子区志留纪苔藓动物变口目2属4种。根据已知属种确认这些苔藓动物化石的时代为早志留世晚期(Late Llandoverian)。根据其地理分布认为北美大陆、欧洲大陆(包括英国,苏联西部)和中国南方、北方大玷,当时彼此相距不远,其间的太平洋、大西洋和下扬子海又彼此相通,属于同一动物地理区(即志留纪北方大区)和同一气候带(即温暖气候带),根据岩相和古生物特征,确认当时苔藓动物的生活环境为平坦海底的陆棚潮下温暖水区。     

浙江长兴灰岩中的龙鱼化石

本文记述了产自长兴阶层型剖面下部的龙鱼化石,其特征与已知属种皆有区别,而与 Saurichthys madagascariensis Piveteau 比较相似.但在鳍的大小,鳞片行数等方面有所不同,今命名为赵氏始龙鱼 (Eosaurichthys chaoi gen. et sp. nov.). 它代表已知龙鱼中最早的记录,证明古生代末期,亚洲这一区域已有龙鱼分布.始龙鱼的发现对了解该类鱼的分布,二叠三叠纪鱼群的演替,以及古地中海的范围,均有重要意义.本文还讨论了龙鱼类鳞列的演变等.     

华南下扬子区的裂齿鱼类化石——华南二叠系—三叠系界线上下鱼类序列研究之二

重新描述了江苏句容与安徽和县的裂齿鱼类化石 ,将华南下扬子区已记述的 2属 5种裂齿鱼类化石初步修订为 1属 2种———江苏张氏鱼 (Zhanginajiangsuensis)和扬子张氏鱼(Zhanginayangtzensis)。由于目前对裂齿鱼类的系统发育关系所知甚少 ,张氏鱼属的系统位置以及相关的动物地理分布问题仍有待深入的研究。     

广西十万大山地区的鱼类区系及其动物地理学分析

于1998年和1999年对广西西南部十万大山地区的鱼类区系进行了调查。十万大山是我国大陆最南端的山脉,该地区共有野生鱼类102种,由于南北坡河流分属不同水系,两地的鱼类组成有很大差异。北坡各支流均汇入明江（珠江水系的一个支脉）,其鱼类组成具有明显的珠江水系特点,在中国动物地理区划上属华南区珠江亚区。南坡各水系多独流入海,鱼类组成与珠江和海南岛诸水系均有较大共性,反映出地史上这些水系之间曾有着广泛的交流和联系,但与海南岛亚区的鱼类区系成分更为接近,动物地理区划应归属海南岛亚区。     

中国鲤科鱼类染色体组型的研究Ⅺ．裂腹鱼亚科二种鱼和鳅鮀亚科三种鱼的染色体组型

裂腹鱼亚科(Schizothoracinae)鱼类主要分布于亚洲高原地区的江河上游,在我国分布有10属,54种和亚种。鳅鮀亚科(Gobiobotitaae)仅有1属3亚属,已知有16种和亚种,在我国分布构就有13种。我们考察的3种鳅鮀亚科鱼类即分属3个不同的亚属。     

The Triassic fish faunas of the Cuyana Basin,Western Argentina

Abstract: The continental deposits of the Cuyana Basin, western Argentina, have yielded the most diverse, but so far almost unstudied, Triassic ichthyofaunas of South America. Here, we review these faunas and show that only eight of the 29 named taxa can be considered valid, including the chondrostean Neochallaia, the acrolepid Challaia, Guaymayenia, a taxon of uncertain affinities, and five species of the perleidiform family Pseudobeaconiidae. The first three taxa most probably come from Middle Triassic sediments, while the pseudobeaconiids are of Late Triassic age. Other material, although not diagnostic, probably represents other species, and thus, the diversity of actinopterygians in the Cuyana basin is certainly higher than currently recognized. For the Late Triassic fish fauna, the absence of crown‐group neopterygians and a single record of a sarcopterygian is noteworthy and probably indicates some degree of endemism in this fauna, also supported by the high abundance of pseudobeaconiids, which are unknown from other areas. Furthermore, on the basis of the age indicated by the fishes and the available geological information, we discuss the age of the local fauna of the Cerro Bayo, close to the city of Mendoza, and the Agua de la Zorra Formation, Uspallata.     

中国海相早三叠世弓鲛鱼类(软骨鱼类)的首次报道——华南二叠系—三叠系界线上下鱼类序列研究之一

广西田东县作登下三叠统罗楼组产出弓鲛鱼类 :作登弓鲛Hyboduszuodengensis(Yangetal.)、乐氏弓鲛H .yohi (Yangetal.)和田东多尖齿鱼 (新种 )Polyacrodustiandongensissp .nov .,其中前二种化石以前曾被作为牙形类报道。这是弓鲛鱼类在中国海相早三叠世的首次报道。另外 ,本组还产出属种未定的硬骨鱼类化石 (Osteichthyesgen .etsp .indet.)。建立了我国海相早三叠世第一个鱼类带化石 ,作登弓鲛—乐氏弓鲛组合带 (Hyboduszuodengensis H .yohiAZ) ;伴生的有Neospathodushomeri N .triangularis牙形类带化石 ,该带化石延续的时限为奥伦尼克阶 (Olenekian)司帕斯期 (Spathian)早期。     

中国海相早三叠世弓鲛鱼类(软骨鱼类)的首次报道——华南二叠系一三叠系界线上下鱼类序列研究之一

广西田东县作登下三叠统罗楼组产出弓鲛鱼类作登弓鲛Hybodus zuodengensis(Yang et al.)、乐氏弓鲛H.yohi(Yang et al.)和田东多尖齿鱼(新种)Polyacrodus tiandongensis sp.nov.,其中前二种化石以前曾被作为牙形类报道.这是弓鲛鱼类在中国海相早三叠世的首次报道.另外,本组还产出属种未定的硬骨鱼类化石(Osteichthyes gen.et sp.indet.).建立了我国海相早三叠世第一个鱼类带化石,作登弓鲛-乐氏弓鲛组合带(Hybodus zuodengensisH.yhoi AZ);伴生的有Neospathodushomeri-N.triangularis牙形类带化石,该带化石延续的时限为奥伦尼克阶(Olenekian)司帕斯期(Spathian)早期.     

Fish ecology and management of the Sepik-Ramu,New Guinea,a large contemporary tropical river basin

Synopsis The ichthyofauna of the Sepik-Ramu basin is composed of diadromous species and the freshwater derivatives of marine families. Fish species diversity, ichthyomass and fish catches are low even by Australasian standards. Three major factors have produced the depauperate ichthyofauna and restricted fishery within the basin: First, the zoogeographic origins of the ichthyofauna. Australasian freshwater fishes, being mainly derived from marine families, generally exhibit ecological characteristics that have evolved for life in estuaries, not rivers. This has led to peculiarities in river fish ecology and explains the probable low fish production from rivers in this region in general. Several important riverine trophic resources are not exploited by the Australasian freshwater ichthyofauna. The modes of reproduction amongst the Australasian freshwater ichthyofauna have limited the colonisation and exploitation of floodplain habitats. Second, Sepik-Ramu lowland habitats, especially floodplains, are very young. This has resulted in low fish species diversity in lowlands, whilst diversity at higher altitudes is equable, in comparison to river systems in southern New Guinea/ northern Australia. Third, the Sepik-Ramu lacks an estuary in sharp contrast to river systems in southern New Guinea or northern Australia. Most of the 18 families of Australasian fishes missing from the Sepik-Ramu are probably absent because of this factor alone. In particular, the Sepik-Ramu has not been colonised by any family of fishes having pelagic eggs, resulting in the loss from the fauna of the few Australasian fish taxa with high reproductive rates. Consequently, the general problems with river fish ecology in Australasia are exacerbated within the Sepik-Ramu by the particular development and morphology of the basin. Fish species diversity in the Sepik-Ramu is low, even in comparison with those taxa representative of marine families resident in rivers in nearby zoogeographic regions (S.E. Asia) whose ichthyofaunas are otherwise dominated by freshwater dispersant groups. The Sepik-Ramu ichthyofauna is considered noteworthy for what is absent, not what is present. Ichthyomass and fish production can be increased by fish species introductions whilst, in theory, biodiversity of the native fish fauna can be maintained. The directions in which ecological evaluations of proposed introductions might proceed in practice for the Sepik-Ramu are discussed but are constrained by the lack of knowledge on species interactions from other areas.     

The Luoping biota: exceptional preservation, and new evidence on the Triassic recovery from end-Permian mass extinction

The timing and nature of biotic recovery from the devastating end-Permian mass extinction (252 Ma) are much debated. New studies in South China suggest that complex marine ecosystems did not become re-established until the middle–late Anisian (Middle Triassic), much later than had been proposed by some. The recently discovered exceptionally preserved Luoping biota from the Anisian Stage of the Middle Triassic, Yunnan Province and southwest China shows this final stage of community assembly on the continental shelf. The fossil assemblage is a mixture of marine animals, including abundant lightly sclerotized arthropods, associated with fishes, marine reptiles, bivalves, gastropods, belemnoids, ammonoids, echinoderms, brachiopods, conodonts and foraminifers, as well as plants and rare arthropods from nearby land. In some ways, the Luoping biota rebuilt the framework of the pre-extinction latest Permian marine ecosystem, but it differed too in profound ways. New trophic levels were introduced, most notably among top predators in the form of the diverse marine reptiles that had no evident analogues in the Late Permian. The Luoping biota is one of the most diverse Triassic marine fossil Lagerstätten in the world, providing a new and early window on recovery and radiation of Triassic marine ecosystems some 10 Myr after the end-Permian mass extinction.     

Two new species of Saurichthys (Actinopterygii: Saurichthyidae) from the Middle Triassic of Monte San Giorgio,Switzerland, with implications for character evolution in the genus

Saurichthys, characterized by a long slender body and an elongated rostrum, is one of the most iconic genera of Late Paleozoic–Early Mesozoic fishes. The genus was particularly speciose in the Triassic, with a global distribution in both marine and freshwater habitats. Here, we describe two new species from the Middle Triassic Besano Formation of Monte San Giorgio, Switzerland, Saurichthys breviabdominalis sp. nov. and Saurichthys rieppeli sp. nov. S. breviabdominalis is characterized by a proportionately long operculum, short abdominal region and rib‐like mid‐lateral scales, whereas S. rieppeli is divergent from other Middle Triassic saurichthyids in the block‐like haemal arches, fringing fulcra on the pelvic and unpaired fins, and reduction of the squamation to a single row in the abdominal region. Phylogenetic analysis places S. rieppeli in a basal position relative to congeners from the Alpine Triassic, and supports previous hypotheses regarding the convergent evolution of reduced squamation within saurichthyids. S. breviabdominalis forms a monophyletic group with species from the same locality, suggesting divergence in sympatry. This finding has implications for our understanding of disparity and character evolution in saurichthyid fishes, as well as ecomorphological divergence and resource partitioning between closely related fishes in Triassic marine ecosystems. © 2015 The Linnean Society of London     

A new stem-neopterygian fish from the Middle Triassic of China shows the earliest over-water gliding strategy of the vertebrates

Flying fishes are extraordinary aquatic vertebrates capable of gliding great distances over water by exploiting their enlarged pectoral fins and asymmetrical caudal fin. Some 50 species of extant flying fishes are classified in the Exocoetidae (Neopterygii: Teleostei), which have a fossil record no older than the Eocene. The Thoracopteridae is the only pre-Cenozoic group of non-teleosts that shows an array of features associated with the capability of over-water gliding. Until recently, however, the fossil record of the Thoracopteridae has been limited to the Upper Triassic of Austria and Italy. Here, we report the discovery of exceptionally well-preserved fossils of a new thoracopterid flying fish from the Middle Triassic of China, which represents the earliest evidence of an over-water gliding strategy in vertebrates. The results of a phylogenetic analysis resolve the Thoracopteridae as a stem-group of the Neopterygii that is more crown-ward than the Peltopleuriformes, yet more basal than the Luganoiiformes. As the first record of the Thoracopteride in Asia, this new discovery extends the geographical distribution of this group from the western to eastern rim of the Palaeotethys Ocean, providing new evidence to support the Triassic biological exchanges between Europe and southern China. Additionally, the Middle Triassic date of the new thoracopterid supports the hypothesis that the re-establishment of marine ecosystems after end-Permian mass extinction is more rapid than previously thought.     

Assessing Genetic Diversity of Brazilian Reef Fishes by Chromosomal and DNA Markers

Little is known on genetics of Brazilian coral reef fish and most of this information is limited to chromosome characterization of major representative species. The diploid chromosome number in marine fish varies from 2n= 22–26 to 2n = 240–260. Despite of this apparent diversity, most studied marine species have a diploid complement with 48 acrocentric chromosomes. This latter trend is mostly observed among Perciformes, an important major taxon of coral reef fishes. Studies in the families Pomacentridae, Pomacanthidae and Chaetodontidae, for example, have shown a common karyotype pattern entirely formed by 48 uniarmed chromosomes. However, rare numerical and structural chromosome polymorphisms and cryptic chromosome rearrangements involving heterochromatin segments and/or nucleolar organizing sites have been reported among such fishes. Although new chromosome forms can contribute to the establishment of genetically isolated populations, their role in reef fish speciation at marine realm still is an open question. More recently, genomic DNA analyses using RAPD and microsatellites, and sequencing and RFLP of mitochondrial DNA have increasingly been used in Atlantic reef fish species. Genetic homogeneity over wide geographical ranges has been reported for different fish groups, in contrast to several cases of population substructuring related to environmental constraints or evolutionary history. Amazonas outflow and upwelling on the Southeastern coast of Brazil are believed to be strong barriers to dispersal of some reef species. Moreover, it is suggested that the pattern of speciation and population structure at South Atlantic is quite distinctive from Pacific Ocean, even when comparing closely related taxa. Further genetic studies are strongly encouraged in Brazilian reef fishes in order to provide a reliable scenario of the genetic structure in this important and diverse fish group.     

Permian–Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution

The Permian and Triassic were key time intervals in the history of life on Earth. Both periods are marked by a series of biotic crises including the most catastrophic of such events, the end‐Permian mass extinction, which eventually led to a major turnover from typical Palaeozoic faunas and floras to those that are emblematic for the Mesozoic and Cenozoic. Here we review patterns in Permian–Triassic bony fishes, a group whose evolutionary dynamics are understudied. Based on data from primary literature, we analyse changes in their taxonomic diversity and body size (as a proxy for trophic position) and explore their response to Permian–Triassic events. Diversity and body size are investigated separately for different groups of Osteichthyes (Dipnoi, Actinistia, ‘Palaeopterygii’, ‘Subholostei’, Holostei, Teleosteomorpha), within the marine and freshwater realms and on a global scale (total diversity) as well as across palaeolatitudinal belts. Diversity is also measured for different palaeogeographical provinces. Our results suggest a general trend from low osteichthyan diversity in the Permian to higher levels in the Triassic. Diversity dynamics in the Permian are marked by a decline in freshwater taxa during the Cisuralian. An extinction event during the end‐Guadalupian crisis is not evident from our data, but ‘palaeopterygians’ experienced a significant body size increase across the Guadalupian–Lopingian boundary and these fishes upheld their position as large, top predators from the Late Permian to the Late Triassic. Elevated turnover rates are documented at the Permian–Triassic boundary, and two distinct diversification events are noted in the wake of this biotic crisis, a first one during the Early Triassic (dipnoans, actinistians, ‘palaeopterygians’, ‘subholosteans’) and a second one during the Middle Triassic (‘subholosteans’, neopterygians). The origination of new, small taxa predominantly among these groups during the Middle Triassic event caused a significant reduction in osteichthyan body size. Neopterygii, the clade that encompasses the vast majority of extant fishes, underwent another diversification phase in the Late Triassic. The Triassic radiation of Osteichthyes, predominantly of Actinopterygii, which only occurred after severe extinctions among Chondrichthyes during the Middle–Late Permian, resulted in a profound change within global fish communities, from chondrichthyan‐rich faunas of the Permo‐Carboniferous to typical Mesozoic and Cenozoic associations dominated by actinopterygians. This turnover was not sudden but followed a stepwise pattern, with leaps during extinction events.     

The evolution of diadromy in fishes (revisited) and its place in phylogenetic analysis

Diadromy is a term used to describe migrations of fishes between fresh waters and the sea; these migrations are regular, physiologically mediated movements which occur at predictable life history phases in each diadromous species, they involve most members of a species' populations, and they are usually obligatory. Around 250 fish species are regarded as diadromous. A review of the life history strategies amongst families of fishes that include diadromous species provides little support for a suggested scenario for their evolution that involves: (1) evolution of anadromy via amphidromy from fishes of marine origins, and (2) evolution of catadromy through amphidromy from fishes of freshwater origins, even though these scenarios seem intuitively reasonable. The various forms of diadromy appear to have had multiple independent origins amongst diverse fish groups. There is increasing confidence that behavioural characteristics of animals are heuristic in gener ating and interpreting phylogenies. However, examination of fishes shows wide variability of diadromous life histories within closely related families and genera, within species, and there is even ontogenetic variation in patterns of behaviour by individual fish. In addition, there is multiple loss of diadromy in many diadromous fish species in which the life history becomes restricted to fresh waters. This variation suggests that diadromy is a behavioural character of dubious worth in determining phylogenetic relationships. Moreover, it appears to have been an ancestral condition in some fish families, such as Anguillidae, Salmonidae, Galaxiidae, Osmeridae, and others, and perhaps in the whole salmonoid/osmeroid/galaxioid complex of families. This, too, makes diadromy of dubious worth in phylogenetic analysis