Well-preserved Early Silurian radiolarians were recovered from siliceous rock fragments contained in a limestone boulder from the Road River Formation, Yukon River area, east-central Alaska. The radiolarians represent five genera, one of which, Parasecuicollacta, is new, and 17 species, nine of which are new: Secuicollacta magnitesta, S. tatondukensis, S. parvitesta, S. alaskensis, Parasecuicollacta bipola, P. hexactina, P. multispinosa, P. nannoglobosa, and Diparvapila pygmaea. Among the 17 species, 11 belong to the family Rotasphaeridae. The ectopically placed spicule, which is the diagnostic characteristic of the subfamily Secuicollactiniinae within the family Haplentactiniidae, is shown to be one of the primary units, a diagnostic feature of the family Rotasphaeridae. Three species are assigned to the family Haplotaeniatumidae, which is newly established in this paper. The family is characterized by the concentric and spiral arrangement of shell with a proloculus and commonly the presence of a pylome, and by the absence of an internal spicule. Several other taxa are extremely rare and are of uncertain taxonomic position. This fauna is characterized by very plentiful rotasphaerids, whereas all the other radiolarian taxa are very rare.
The Road River fauna is similar to that from the Cherry Spring Chert of Nevada, thought to be late Rhuddanian based on a sparse graptolite fauna, and is very similar to an unreported Early Silurian Canadian Arctic fauna, whose stratigraphic range based on the graptolite fauna is within the early Telychian. Conodonts, chitinozoans, scolecodonts, and graptolites were also recovered from the siliceous rock fragments. Five genera and seven species of chitinozoans, four genera and five species of conodonts, and two uncertain taxa of graptolites were identified. Their biostratigraphy indicates that the Alaskan radiolarian fauna belongs to the upper Aeronian to lower Telychian of the Llandoverian.