The tubarium construction of Lower Ordovician (Dapingian) Baltograptus species (Graptolithina) from Dalarna, Sweden

Isolated and chemically bleached graptolite specimens of the genus Baltograptus from Skattungbyn, Dalarna (central Sweden) reveal important new information on the internal construction of the tubarium. The specimens show the typical metasicular origin of th11 and the presence of numerous longitudinal rods in the prosicula. The investigation provides some insight into intraspecific variation and on the differentiation of individual species. It also provides information on the early evolution of the two-stiped dichograptids (‘section Didymograpti’ in Bulman 1970). Three distinct species, identified as Baltograptus minutus, Baltograptus kurcki and Baltograptus extremus n. sp. can be recognized in the collection of hundreds of specimens. The Baltograptus species are associated with a diverse Dapingian graptolite fauna, prepared by Roland Skoglund, but never investigated in detail, including specimens of Pseudophyllograptus densus, Acrograptus gracilis and other taxonomically and biostratigraphically important taxa.