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下—中泥盆统界线层二个牙形石种的演化及比较

EVOLUTION AND COMPARATIVE ANALYSIS OF TWO CONODONT SUBSPECIES NEAR THE LOWER-MIDDLE DEVONIAN BOUNDARY
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摘要 Polygnathus costatus partitus(肋多颚牙形石分亚种)是国际地层委员会(ICS)确定的中泥盆统底部的标准化石,但它与共存的Polygnathus lingui formisbultyncki在形态上难以区分,造成地层划分的困难。经过认真研究,Polygnathuscostatus partitus依据基腔位置可以划分出幼年期和成年期两个发育阶段。Poly-gnathus linguiformis bultyncki依据表面形态可以划分为幼年期、青年期和老年期三个发育阶段;通过两者不同发育阶段的比较研究,笔者提出了三点不同以在鉴定中将两者加以区别,从而提高化石鉴定的精度。 Polygnathus costatus partitus is the standard fossil at the base of the MiddleDevonian. But it is difficult to distinguish it in morphology from Polygnathuslingui formis bultyncki occurring together with Polygnathus costatus partitus,which makes it difficult to define the Lower-Middle Devonian boundary. Detailedstudy shows that two developmental stages (young stage and adult stage) ofpartitus may be distinguished on the basis of the position of the cavity. Theontogenetic development of bultyncki involves three stages (larval stage, youngstage and adult stage) on the basis of its morphology. Comparison of the develo-pmental stages of the two subspecies reveals three differences between partitusand bultyncki, 1. Partitus's carina reaches the posterior end during its very early stage andretains this position through life; but bultyncki's carina oversteps the posteriorend of the platform during its larval stage, and terminates before the tongue duringthe young stage and adult stage. 2. The inner and outer posterior margins of partitus are characteristicallystraight, converging, to form a sagittat outline;whereas bultyncki develops a tongue. 3. The cavity of partitus of young stage oversteps the anterior end of the pla-tform and is located near the anterior end of the platform during its adult stage;but the cavity of bultyncki is located near the anterior end of the platform inthe larval stage and at one third length of the platform in the young stage andadult stage. These results supply the evidence for the fossil identification.
出处 《地质论评》 CAS CSCD 北大核心 1993年第2期130-137,T001,共9页 Geological Review
基金 国家自然科学基金(项目编号49102018) 国家教委基金
关键词 牙形石 演化 川类 下泥盆世 界线层 Lower--Middle Devonian conodont ontogenetic development
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参考文献3

  • 1白志强,1988年
  • 2白顺良,广西及邻区泥盆纪生物地层,1982年
  • 3白顺良,北京大学学报,1979年,4期,57页

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