Published online by Cambridge University Press: 01 May 2009
Horizons characterized by the trilobites Staurocephalus clavifrons and/or Phillipsinella parabola have long been regarded as significant in Upper Ordovician correlation. From time to time this idea has been formalized by the erection of Phillipsinella parabola or Staurocephalus clavifrons Zones or by equating the range of a ‘Phillipsinella parabola fauna’ with Series sub-divisions within the Standard Ordovician succession. At the present time the Phillipsinella parabola-Staurocephalus clavifrons fauna is widely regarded as indicating a Rawtheyan age (Ashgill Zones 5–7).
Recent work by the author, however, together with a review of available evidence from the literature casts grave doubts on the validity of such concepts. It is suggested that in some areas the Phillipsinella parabola-Staurocephalus clavifrons fauna may range at least as low as basal Cautleyan (Ashgill Zone 1).