臺南左鎮區二寮棘皮動物化石之研究

Abstract

本研究透過形態觀察及特徵比較，針對產自臺南左鎮二寮出露之崎頂層中，總計27件共33隻的海星與 100 件海膽化石進行分類研究；另，經由化石泥質圍岩中所含超微化石分析，其地層年代相當位於 0.61-0.99Ma 區間（莊智凱，未發表）。所有海星化石：外形均呈星形、腕數為 5 腕、腕之切面呈長方形、口面與反口面均呈平坦、體盤相對較小、上緣板與下緣板均明顯且對稱、緣板外形呈長方形且板上覆滿顆粒體與偶帶有棘刺、帶線明顯，以及背板較小且呈小柱體狀等共同特徵，可同歸屬於柱體目( Paxillosida )中的槭海星科( Astropectinidae )。再依據：背板大小、數量與排列；上、下緣板大小；腹板數，以及步帶溝寬窄等細部差異，可區分出5件槭海星( Astropecten )與24件鑲邊海星( Craspidaster )；但由於化石大多缺少鑑種特徵，目前僅能從中鑑定出 2件華普槭海星近似種 A. cf. vappa 與 4 件黃昏鑲邊海星近似種 C. cf. hesperus。另外，這批海膽化石標本雖然幾乎皆為內鑄型保存，且有不等程度的受壓變形，僅有極少數的化石標本上有肛下帶線的殘留，但根據海膽化石形態特徵：外殼呈偏圓心形、殼長與寬幾乎相等；反口面殼後方比前方高、殼最高處在後方的第 5 間步帶、頂系靠近殼後方、前方步帶寬且中等程度凹陷、辮狀步帶靠近內帶線處寬而殼緣處細、辮帶上有排列整齊且兩兩成對的步帶孔、無環瓣帶線、大型殼疣；在口面，靠近殼前側口圍凸出、唇板凸起、肛門呈現稍長的橢圓形等特徵，可將這些海膽歸屬於猬團目( Spatangoida )、拉文海膽科( Loveniidae )、棘心海膽屬( Echinocardium )，並且鑑定為同一種 E.cordatum。本研究報告臺灣地區最年輕海星化石，是臺灣首次槭海星與鑲邊海星化石紀錄，也很可能是世界上首次報導鑲邊海星化石。Through morphological observation and characteristic comparison, this study conducted a classification study on a total of 33 starfish and 100 sea urchin fossils from the Erliao area, Zuojhen, Tainan. In addition, through the analysis of the nanofossils contained in it shows that its age is in the range of 0.61-0.99 Ma (Chih-Kai Chuang, unpublished). All starfish fossils: bodies are star-shaped, have 5 arms, arms have a rectangular section, oral and aboral are flat, disk relatively small, and superomarginals and inferomarginals are obvious and symmetrical. The marginals are rectangular in shape and covered with granules, with spines and fascioles. The abactinals are small and paxilliform. They can be classified to order Paxillosida and family Astropectinidae. Based on the following characteristic: the size, number and arrangement of the abactinals; the size of the superomarginals and inferomarginals; the number of actinals; and the width of the ambulacral groove, 5 Astropecten and 24 Craspidaster can be distinguished. However, because most of the fossils lack identification characteristics, only 2 A. cf. vappa and 4 C. cf. hesperus can be identified from them. In addition, although these sea urchin fossil specimens are almost all preserved in casts and have varying degrees of compression deformation, only a few fossil specimens have subanal fasciole. However, according to the morphological characteristics of sea urchin fossils: test is heart-shaped, and the length and width of the test are almost equal. On the aboral, the back of the test is higher than the front, the highest part of the test is in the fifth interambulacrum, the apex system is close to the back of the test, the front ambulacrum is wide and moderately sunken. The petaloid is wide near the internal fasciole and thin at the ambitus. The petaloid has neatly arranged and paired ambulacral pores. No peripetalous fasciole and large tubercle. On the oral, the peristome is convex near the front side of the test. These sea urchins can be classified into the order Spatangoida, Loveniidae, and Echinocardium, and can be identified as the same species, E. cordatum. This study reports the youngest starfish fossil in Taiwan. It is the first record of Astropecten and Craspidaster fossils in Taiwan. It is also probably the first report of Craspidaster fossils in the world.