Relationships between the morphologic rates of diatom evolution and north Pacific Miocene circulation

从太平洋新近纪到第四纪，已报道了几种具有褶皱瓣面的中心硅藻，年龄约为0-17 Ma；雅贝海链藻群(=Thalassiosira brunii，T.fleosa，T.grunowii，T.miopicata，T.moholensis，T.Praeyabe.，T.temei，T.Yabe.等)。这些形状都有一个非常相似的形状，一边是凸形，另一边是凹形，中间形状在各个形状中很常见。为了提供中新世北太平洋高硅藻产量与中新世北太平洋古气候和古海洋变化之间关系的信息，对11种形态类型的瓣膜尺寸进行了测量。生物统计学证据表明：1)这条进化线上的种群是普雷雅贝，2)中新世中期(15-13 Ma)形态演化速率增加，3)普雷贝斯在这一时间间隔及其周围进化出了几个后代。这种形态演化速率的增加可能与异位体的形成有密切关系，这可能部分是由于中中新世冷事件导致的强烈的上升流和高硅藻产量所致。这一谱系还将在太平洋新近纪的硅藻带状方案中定义新的生物带，并将在接下来的工作中提出一个新属--Plicatodisus。

Several centric diatoms having plicate valve face have been reported from Pacific Neogene to Quaternary ranging in age from approximately 0 to 17 Ma ; Thalassiosira yabei group (=Thalassiosira brunii, T.flexosa, T.grunowii, T. mioplicata, T.moholensis, T.praeyabei, T.temperei, T.yabei, and others). These forms share a quite alike plication, one side convex and other side concave, of valve and intermediate forms occur fairly commonly among forms. Hence it appears that these plicated forms seem to be on the same evolutionary line.To provide information for the relationship between the morphologic rates of evolution of T.yabei group and mid Miocene high diatom production associates with Miocene North Pacific paleoclimatic and paleoceanographic changes, measurements of valve dimensions were made on 11 morphotypes, classified in this study, from Middle to Late Miocene part of their evolutionary line.The biometric evidence suggests that 1) the stock of this evolutionary line is T. praeyabei, 2) morphologic rates of evolution increases in Middle Miocene (15-13Ma), and 3) several descendants evolve from T.praeyabei at and around the interval. This increases in morphologic rates of evolution might have close relationship to auxospone formation which may be partly caused by intensified upwelling and high diatom production associated with mid Miocene cold events.This lineage also will define new biozones in a diatom zonal scheme for the Pacific Neogene, and a new genus, Plicatodiscus will be proposed in a following work.