Abstract

Hystricurus millardensisHintze, 1953 has been recorded widely in Laurentia. Revision on the basis of abundant new silicified topotype material indicates that most of these records are of morphologically distinct, though related, taxa and that a plexus of related species is involved. The new genus Millardicurus, with H. millardensis as type, is proposed for this clade, which also includes two well-documented new species, M. housensis and M. paramillardensis, from the House Formation of western Utah, several named species from Greenland, and several unnamed new species from various parts of Laurentia that have in the past been referred to M. millardensis. Millardicurus is not apparently closely related to younger Skullrockian–Stairsian hystricurids from Laurentia, but may be related to poorly known coeval Siberian Platform species classified in the genus NyayaRozova, 1963. Landmark-based geometric morphometric methods comprising principal component analysis of partial warp scores and Goodall's F test of pairwise means indicate significant shape differences among cranidia, librigenae, and pygidia of the House Formation species of Millardicurus.

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