早奥陶世Sinograptus typicalis Mu胞管形态研究补遗

A STUDY OF THE THECAL MORPHOLOGY OF EARLY ORDOVICIAN SINOGRAPTUS TYPICALIS:AN ADDENDUM

早奥陶世Sinograptus typicalis Mu笔石胞管形态对于理解其生态具有重要意义。本文在原有研究基础上,重新解释Sinograptus笔石胞管形态特征及其生态。Sinograptus两个笔石枝均保存了一个完整的胞管,在一个胞管的长度内,共有三个胞管背褶和三个腹褶。第一个背褶是该胞管(thn)的原胞管背褶,随后胞管延伸经过中间的背褶(胞管thn+1的原胞管背褶)下面,有一个曲尺式(L型)的弯曲,然后在延伸到胞管thn+2的生出位置(thn+2的原胞管褶)时向下延伸成一个与笔石枝呈近垂直的腹褶,胞管末端为胞管口部。左侧笔石枝胞管可见缝状的胞管口,而右侧笔石枝的胞管仅见胞管口部的背方,反映了Sinograptus两笔石枝胞管口的朝向方向是相反的,表明其悬浮于水中时很可能是缓慢旋转的,水动力较弱。Sinograptus发育明显的背褶刺和腹褶刺,表明其为热水型的、具刺的狭温型属。因此,Sinograptus基本上处于温暖的海水,在相对静水中呈悬浮状态。

Thecal morphology of the Sinograptus typicalis Mu is crucial to understand its ecological environment. This study re-presented thecal morphological features of Sinograptus and reinterpreted its ecological environment on the basis of previous studies.Two stipes of the Sinograptus were reconstructed and each has a complete thecal,which comprises three dorsal thecal folds and three ventral thecal folds.The first dorsal thecal fold is prothecal fold of the thecal（thn）,which extends beneath the second dorsal thecal fold（prothecal fold of thecal thn＋1）,forming an L-shape curve.Subsequently,the thecal develops a ventral thecal fold that is perpendicular to the stipe beneath the prothecal fold of thecal thn＋2.Thecal apertures are present at tip of the thecal.Crevice-like thecal apertures with transverse expansion occur at the upper part of the thecal in the left-hand side stipe,whereas only the dorsal part of thecal apertures is observed in the right-hand side stipe,showing that the thecal apertures on the left-and right-hand side stipes of the Sinograptus point to opposite directions.This indicates that the Sinograptus suspended and rotated slowly within a low-energy hydrodynamic environment.Spines of dorsal and ventral thecal folds are well developed in the Sinograptus, suggesting that they are spine stenothermal species living in warm water.Therefore,Sinograptus suspended in warm marine water with weak hydrodynamics.