摘要
苔藓动物是一类多为海生、滤食性的群体生物。奥陶纪是苔藓动物发生、演化辐射和灭绝的重要时期,也是苔虫礁形成的最早时期。已知最老的化石苔藓动物发现于中国特马豆克晚期。构成苔藓动物基本分类框架的狭唇纲(包括变口目、隐口目、泡孔目和管孔目)和宽唇纲(包括窗孔目和栉口目)也都是在奥陶纪时期逐步形成的,其中,变口目出现于特马豆克期Tr2时间段,在弗洛期和大坪期,多样性较低,但从达瑞威尔期开始,经桑比期至凯迪期,多样性不断增高,并出现辐射。隐口目(特别是"双叶类隐口目苔虫")也经历了与变口目相类似的发展过程,但它首次出现的时间要相对略迟于变口目。这两个目在整个奥陶纪苔藓动物群中一直占据主导地位。泡孔目、管孔目和窗孔目,先后首次出现在弗洛期Fl2时间段、大坪期Dp1和Dp2时间段,但它们在整个奥陶纪期间一直处于低多样性态势。至于栉口目,它首次出现的时间可能更迟,在凯迪期Ka4时间段,犹如昙花一现。苔藓动物的演化在接近奥陶纪末时呈两幕式灭绝,一次发生在凯迪期Ka2时间段(可能相当于塔凯和安斯蒂的"拉夫塞伊灭绝"),另一次发生在赫南特期Hi2时间段(可能相当于塔凯和安斯蒂的"赫南特灭绝")。分子生物学和形态学证据表明,苔藓动物属原口动物,而不是以前长期认为的后口动物,或介于原口动物和后口动物之间的过渡类型;而且,苔藓动物与腕足动物、帚形动物之间没有直接的亲缘关系。苔藓动物可能起源于一种叫原内肛动物的生物,它们的目一级分类单元之间的系统发育关系目前尚未形成共识,本文绘制的谱系图还有待于化石记录的不断补充和分子生物学研究的逐步介入以使其日趋完善。
Bryozoans are important marine suspension-filter feeding colonial animals whose origins and evolution remain enigmatic.The Ordovician Period has great significance for the origination,radiation and extinction of bryozoans,and also for formation of bryoherms.The oldest known bryozoans are found in the strata of Fenhsiang Formation（Late Tremadocian）of China,and nearly all recognized orders of bryozoans including Stenolaemata（Trepostomida,Cystoporida,Cryptostomida,Tubuliporida）and Eurystomata（Ctenostomida and Fenestrida）appeared successively throughout the Ordovician.Within bryozoans,Trepostomida and Cryptostomida first appeared in Tr2 of the Tremadocian,and maintained relatively low diversity in the Floan and Dapingian.Their diversity increased beginning in the Darriwilian,and a major radiation occurred from the Sandbian through the Katian.Compared to Trepostomida,Cryptostomida（specifically,the bifoliates）show similar evolutionary trends,but appeared later.Both groups of bryozoans were the dominant forms during the entire Ordovician.Cystoporida,Tubuliporida and Fenestrida made their first respective appearances in Fl2 of the Floan,and Dp1 and Dp2 of the Da-pingian,but their diversity remained relatively low for the remainder of the Ordovician.Ctenostomida first appeared much later than the others,in Ka2 of the Katian.Two extinction episodes occurred during the Ordovician evolution of bryozoans,the first taking place in Ka2（Rawtheyan extinction）,and the second during Hi2 of the Hirnantian.Both molecular and morphological evidence suggest that bryozoans are protostomes,not deuterostomes as traditionally viewed,nor an intermediate group between them.Results of both molecular and morphological analyses have shown no obvious relationships between Brachiopoda,Phoronida and Bryozoa.Bryozoans may have originated indepen-dently from so-called ancient ＂Proentoprocta＂,and no agreement exists on the relationships between the orders.The phylogenetic relationships pre-sented in this paper need to be teste
出处
《古生物学报》
CAS
CSCD
北大核心
2010年第2期139-163,共25页
Acta Palaeontologica Sinica
基金
中国科学院南京地质古生物研究所现代古生物学和地层学国家重点实验室基础性项目研究课题(批准号:20092103)资助
关键词
苔藓动物
狭唇纲
宽唇纲
多样性演变
种系发生
辐射
灭绝
Bryozoans Stenolaemata Eurystomata diversity changes phylogeny radiation extinction
