Ptiloncodus Harris, 1962, a hook-shaped microfossil, is present in late Floian through Hirnantian [ = late Ibexian through Gamachian] rocks in regions marginal to Laurentia. Specimens from the Great Basin provide additional information about this enigmatic microfossil. Two fused clusters of Ptiloncodus elements from western Utah do not duplicate clusters reported previously from coeval strata in central Nevada. EDS spectra confirm the long-standing assumption that these fossils are composed of calcium phosphate. SEM images show that short crystallites are aligned to provide fibrous surficial ultrastructure in the hooked part of these fossils, but more open arrangement is displayed at the top of the shank where paired lobate structures are attached. The join between the lobes and the shank is weak; these two parts of the fossil separate easily so that most specimens did not retain lobes. The shanks end in rounded terminations or in paired knobs that range from low protuberances to near horn-like features. The new data do not support any of several suggestions that compare Ptiloncodus to extant organisms, and uncertainty continues about its affinity and the function of its skeletal elements.
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Vol. 84 • No. 1