笔石
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(笔(bǐ )石(shí ),笔(bǐ )石(shí ))
古(gǔ )代(dài )的(de )一(yī )种(zhǒng )体(tǐ )内(nèi )有(yǒu )骨(gǔ )骼(gé )的(de )无(wú )嵴(jí )椎(zhuī )动(dòng )物(wù ),形(xíng )体(tǐ )很(hěn )小(xiǎo ),生(shēng )活(huó )在(zài )平(píng )静(jìng )的(de )海(hǎi )洋(yáng )中(zhōng ),构(gòu )成(chéng )羽(yǔ )毛(máo )状(zhuàng )或(huò )锯(jù )齿(chǐ )状(zhuàng )的(de )群(qún )体(tǐ )。页(yè )岩(yán )中(zhōng )常(cháng )有(yǒu )它(tā )的(de )化(huà )石(shí ),是(shì )划(huá )分(fèn )和(hé )对(duì )比(bǐ )地(dì )层(céng )的(de )重(zhòng )要(yào )化(huà )石(shí )之(zhī )一(yī )。
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