Abstract

Well-preserved Middle Cambrian radiolarian were recovered from the Beetle Creek Formation, Inca Formation, and Devoncourt Limestone, Georgina Basin, Australia. Unlike previously reported Early Paleozoic radiolarians, these Middle Cambrian Radiolaria have two diagnostic characteristics in common with siliceous sponge spicules that occur in the same faunas: their skeletal elements consist of hollow tubes, and when a spicule is present, all spicular skeletons, including the internal spicule, are point-centered. The faunas contain 6 new genera and 18 new species; most of them have one or more spicular skeletons. Two new families are established. One family has a spherical shell wall with one or more point-centered internal spicule(s); it is named here Archeoentactiniidae n. fam. and consists of three new genera, Archeoentactinia, Fungomacula, and Spongomassa. The other new family, Palaeospiculumidae n. fam., consists of a point-centered spicular skeleton without a spherical shell capsule; the family is composed of the single genus Palaeospiculum n. gen. The taxa belonging to this family might perhaps be considered to be sponge spicule, but they differ from sponge spicule because their skeleton has the same basic structure as in Palaeoscenidiidae, that is, the spicule consists of apical and basal rays. In addition to these genera belonging to the two families, two other genera are present. They are uncommon and are of uncertain taxonomic position at the family level. One of the two, Aitchisonellum n. gen., has a spherical shell without internal spicule, but it belongs to neither Inaniguttidae Nazarov and Ormiston 1984 nor Palaeoactinosphaeridae Noble 1994; it seems to fit best in the informal group of Palaeoactinomiids Holdsworth (1977). The other genus, Protobiramus n. gen., has no typical internal spicule, but consists of a biaxially arranged four-rayed spicule and repeatedly bifurcated branches of those rays; the branch tips are not merged. The difference in faunal compositions among the three Middle Cambrian formations examined is not great: the Beetle Creek Formation, Inca Formation, and Devoncourt Limestone faunas consist of 7, 23, and 8 species, respectively.

First Page Preview

First page PDF preview
You do not currently have access to this article.