Systematics and affinity of the lower Ordovician (Tulean; lower Floian) trilobite Psalikilopsis

Jonathan M. Adrain, Neo E.B. Mcadams, Stephen R. Westrop, Talia S. Karim

Research output: Contribution to journalArticlepeer-review

11 Scopus citations


Psalikilopsis Ross, 1953, has been known from a single species and interpreted as a " hystricurine" ancestral to some, but not all, " bathyurids" . Comprehensive revision of the type species and the description of three new species demonstrate that the taxon is ingroup Bathyuridae. The unusual morphology of its more derived species is associated with a change from normal bathyurid sphaeroidal enrolment to spiral enrolment, with part of the pygidium tucked inside the cephalon, stopped medially by a pygidial spine docking against a medially modified anterior border. The oldest and apparently basal species lacks these modifications and is of " normal" bathyurid morphology. The genus occurs in lower Floian (Tulean) Psalikilus spinosum, Hintzeia celsaora, and Psalikilopsis cuspidicauda zones in Idaho, Utah, and Nevada, and its striking morphology and common occurrence make it biostratigraphically significant. A pygidium from the Fort Cassin Formation of New York, and two species illustrated in open nomenclature from the Shallow Bay Formation of Newfoundland demonstrate the occurrence of Psalikilopsis in eastern Laurentia. The eastern Laurentian species appear to be younger than those from western Laurentia. New species are Psalikilopsis paracuspidicauda (Psalikilopsis cuspidicauda Zone), P. redfordi (H. celsaora Zone), and P. newmani (Psalikilus spinosum Zone).

Original languageEnglish
Pages (from-to)369-416
Number of pages48
JournalMemoirs of the Association of Australasian Palaeontologists
Issue number42
StatePublished - 2012


  • Bathyuridae
  • Floian
  • Idaho
  • Nevada
  • Silicified
  • Systematics
  • Trilobita
  • Tulean
  • Utah


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