The early Ordovician (late Tremadocian; Stairsian) dimeropygid trilobite 'Pseudohystricurus' Ross

• Published in: Memoir ... of the Association of Australasian Palaeontologists no. 45; pp. 215 - 232
• Main Authors: Jonathan M Adrain, Talia S Karim, Stephen R Westrop
• Format: Journal Article
• Published: 01.05.2014
• Subjects: Collectors and collecting; Trilobites; Type specimens
• ISSN: 0810-8889

The Early Ordovician genus 'Pseudohystricurus' Ross has been treated as a minor taxonomic wastebasket for poorly known species featuring small, dorsally convex cranidia and tuberculate sculpture. No previously assigned species apart from the type species appear to belong to the genus. The type species, 'P. obesus' Ross, has been known in its type area from only a single cranidium. New collections demonstrate that it is confined to the recently proposed 'P. obesus' Zone, the uppermost trilobite zone of the Stairsian Stage. The species is revised on the basis of new collections from the type locality in the Garden City Formation, southeastern Idaho, and from the Fillmore Formation, western Utah. The genus is known from the underlying 'Pseudoclelandia cornupsittaca' Zone from a species described in open nomenclature from the Fillmore Formation. The oldest known species is 'P. wigglesorum' sp. nov., from the 'Bearriverops alsacharovi' Zone of the Garden City Formation. Details of developmental morphology revealed by silicified specimens offer compelling evidence that 'Pseudohystricurus' is closely related to the Middle - Late Ordovician 'Dimeropyge Opik'.