Major Subgroups

Order Graptoloidea (Subphylum Stomochordata, Class Graptolithina) Existed from the Lower Ordovician to Lower Devonian. Rhabdosomes originally had up to eight stipes, in later forms this number was reduced to two or even one. Thecae occur on one or both sides of the stipe and show a high morphological diversity. There are three suborders: 1) Anisograptidae (Lower Ordovician), 2) Dichograptina (Ordovician) and 3) Virgellina (Ordovician-Devonian).
Order Dendroidea (Subphylum Stomochordata, Class Graptolithina) Existed from the Middle Cambrian to Lower Carboniferous. Rhabdosomes are highly branched. Thecae are numerous and of two types: 1) autothecae and 2) bithecae. There are three families: 1) Acanthograptidae (Upper Cambrian-Middle Devonian), 2) Dendrograptidea (Middle Cambrian-Carboniferous) and 3) Ptilograptidae (Lower Ordovician-Upper Silurian).
	Chart showing the evolution of graptolite form. Specimens within the Order Graptoloidea, are characterized by rhabdosomes with relatively few stipes. Thecae are normally situated on one or both sides of the stipe. Specimens representative of the Order Dendroidea, are characterized by rhabdosomes with numerous stipes. Thecae are numerous and can be of two types: autothecae or bithecae (large, single theca, ot small, numerous thecae).       Chart reproduced with permission of ENK Clarkson

Author: LShychoski
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