Revision of zonal and related graptolites of the Lancefieldian–Bendigonian (early Floian) graptolite sequence in Victoria

Abstract

The topmost Lancefieldian (La3, earliest Floian, Early Ordovician) Paratetragraptus approximatus Biozone of Victoria contains a previously undocumented graptolite fauna that includes, in addition to the nominative species, Paratetragraptus cooperi sp. nov., P. thomassmithi sp. nov., P. acclinans, P.? henrywilliamsi sp. nov., and Tshallograptus cymulus gen. et sp. nov., interpreted as the direct ancestor of Tshallograptus fruticosus (J. Hall). Taxa such as Kinnegraptus, Laxograptus, Pseudobryograptus, Phyllograptus, Tetragraptus and Loganograptus also make their first appearance in this zone. The succeeding Bendigonian stage, traditionally subdivided into four biozones using overlapping ranges of P. approximatus and the four- and three-stiped morphs of the T. fruticosus clade, is revised to accommodate the earlier than documented appearance of the 3-stiped morph, here renamed Tshallograptus tridens sp. nov., in the Be1 Biozone. The new subdivision consists of three biozones: Be1 P. approximatus + T. fruticosus Biozone, Be2+3 T. fruticosus + T. tridens Biozone, and Be4 T. tridens Biozone. T. tridens is vanishingly rare in Be1 and Be2 but appears in abundance in Be3 which is retained as a local subzone.