Any of numerous extinct colonial marine animals chiefly of the orders Dendroidea and Graptoloidea of the late Cambrian to the early Mississippian periods, whose fossil remains are often used to date the rocks of the Silurian and Ordovician ages.

• 笔石动物许多已绝灭的殖民地海洋生物中的任何一种，主要为寒武纪晚期到密西西比纪早期的树形笔石目及笔石纲的生物，其化石残存物常用于确定志留纪和奥陶纪岩石的年代