贵州寒武纪始海百合类萼部形态定量评价及其意义

QUANTITATIVE ASSESSMENTS AND IMPLICATIONS ON THECAL MORPHOLOGY IN CAMBRIAN EOCRINOIDS FROM GUIZHOU PROVINCE

始海百合类是贵州寒武纪杷榔动物群和凯里生物群代表性化石类群。产出杷榔动物群和凯里生物群的杷榔组和凯里组主要由灰绿色、灰色的泥、页岩组成,始海百合类化石保存在2个组中上部的泥、页岩中,化石保存好,丰度高,是陆棚斜坡较深水环境生态类群的典型代表。本文基于来自杷榔组的36块Guizhoueocrinus yui,29块Protogloboeocrinus yini标本,和凯里组的20块Sinoeocrinus lui,20块Globoeocrinus globulus标本,采用几何形态测量方法和传统形态测量方法,对每块标本萼部选定了4个界标点(landmark),进行数理统计和几何形态的定量分析。发现寒武纪始海百合类的萼部尺寸上差异较小,在形态上,杷榔组的Protogloboeocrinus yini和Guizhoueocrinus yui萼形相似,均偏细长形,而凯里组的Sinoeocrinus lui和Globoeocrinus globulus萼形差异较大,口部区域宽度均出现增大,萼茎连接处宽度则出现变大和变小两种趋势。结果说明:同一生态环境下寒武纪早期的Guizhoueocrinus yui,和中期的Sinoeocrinus lui的萼在演化上具连续性,细长的萼与长茎能够让始海百合个体更有效捕食上部水域的食物,而寒武纪早期的Protogloboeocrinus yini和中期的Globoeocrinus globulus的萼在形态上具有演化上的连续性。球状的萼配合粗短的茎,可以增强始海百合个体的稳定性,以适应更强的水动力环境,表明出现了生态位的扩张。

Eocrinoids are a representative fossil group of the Cambrian Balang biota and Kaili biota.The Balang Formation and the Kaili Formation, containing Balang biota and Kaili biota,are mainly composed of green-grey mudstone and shale. Eocrinoids,a typical ecological group in outer shelf deep-water facies,are well-preserved in large amounts in middle-upper part of the Balang Formation and the Kaili Formation.Based on measured data of thecal morphology (including landmark data and linear distances)of 105 samples among 4 species:36 Guizhoueocrinus yui,29 Protogloboeocrinus yini,20 Globoeocrinus globulus and 20 Sinoeocrinus lui,we use traditional morphometric method and geometric morphometric method to investigate the morphological variation of thecal morphology of 4 eocrinoid species.The results show that little difference can be found in thecal size.Morphological variation of theca between Protogloboeocrinus yini and Guizhoueocrinus yui is relatively small,they commonly share an amygdaloidal form.However,theca shape between Sinoeocrinus lui and Globoeocrinus globules exhibits a significant variation,which indicates an evolutionary divergence. compared to eocrinoids (Protogloboeocrinus yini and Guizhoueocrinus yui )from the Balang Formation,eocrinoids (Globoeocrinus globulus and Sinoeocrinus lui)from the Kaili Formation develop a wider oral area and larger/smaller part at the bottom of the theea.In addition,in Sinoeocrinus lui,the theca develops a conical shape.However, in Globoeocrinus globulus,the theca develops a global shape.The result indicates that there is a continuous evolutionary trend in early-middle Cambrian eocrinoids.Conical theca and stem can enlarge the feeding area,while spherical thecal and short stem can make individuals adjust to stronger water energy,by attaching to the sea floor or biodebris more tightly.This study demonstrates that there may occur an ecological niche expansion of eocrinoids in Cambrian Series 2 and Series 3.