New Ordovician marine macroalgae from North America, with observations onButhograptus,Callithamnopsis, andChaetocladus

Abstract

AbstractOrdovician material from the Platteville Formation (Sandbian) of southern Wisconsin and Big Hill Formation (Katian) of northern Michigan is described that provides novel information about the phylogenetic affinity, taxonomic diversity, and stratigraphic range of the nonbiomineralized taxaButhograptus,Callithamnopsis, andChaetocladus. Two new species ofButhograptus, a previously monotypic genus, are erected on the basis of the Platteville Formation material,Buthograptus gundersonin. sp. andB.meyerin. sp., and new occurrences ofB.laxusare recorded from several localities and two distinct stratigraphic levels within this unit. On the basis of scanning electron microscopic investigation of the material and the fact that each of the threeButhograptusspecies has a close counterpart in the frond morphology of an extant species ofCaulerpa,Buthograptusis interpreted as a member of the green algal order Bryopsidales. New specimens from the Platteville Formation assigned toCallithamnopsisreveal new morphological details for the type species,C.fruticosa(Hall, 1865), aspects of which indicate that the genus belongs to the family Triploporellaceae rather than Seletonellaceae within the green algal order Dasycladales, andChaetocladusmaterial from the Big Hill Formation includes specimens that are formally assigned toChaetocladus dubius(Spencer, 1884), a species of dasycladalean alga known previously only from the mid-Silurian of Ontario.