伦敦圣·乔治医学院解剖学家P.N.Dilly认为.大约3亿年前绝迹的笔石类现在也许仍潜伏在未勘探过的深海中.笔石类极为常见,它起源于5～5.7亿年前的寒武纪,后来进化出多种形式,这类化石在对比不同区域岩层年代时非常有用.Dilly认为笔石以前被错误地分了类,它其实是半索动物纲羽鳃类.这样它就成了人类的远亲和脊 PNDilly, an anatomist at the St. George’s School of Medicine in London, believes that the extinct penoliths about 300 million years ago may still lurk in unexploited deep seas.Cephalothreys are very common and originated from about 570 million to 570 million years ago Cambrian, later evolved in many forms, such fossils in different regions of the rock age comparison is very useful .Dilly think the stone was wrongly divided before the class, it is actually half-gill animal Gang Yu class so it It has become a human distant relatives and ridges