Morphological assessment of the earliest paradoxidid trilobites (Cambrian Series 3) from Morocco and Spain

A Cambrian immigration event of paradoxidid trilobites has traditionally marked some regional lower-middle Cambrian boundaries in the Acado-Baltic subprovince (including Baltica and the Mediterranean and Avalonian margins of West Gondwana). The earliest paradoxidine species in Morocco and the Iberian Peninsula have been used as a chronostratigraphic link to support the definition of a common base for the Cambrian Series 3, but recent studies have proposed new species without revising previously established ones. This paper offers a morphological statistical analysis based on both linear measurement and landmark-based geometric morphometric approaches performed on the earliest paradoxinine trilobites sampled in the Anti-Atlas (Morocco) and the Iberian Chains (Spain). As a result, the diagnosis of Acadoparadoxides mureroensis is emended and several species recently erected in Morocco (A. cf. mureroensis, A. levisettii, A. ovatopyge and A. pampalius) are suggested as synonyms of A. mureroensis until 3D statistical analyses are available based on material preserved on carbonate or silica nodules. The first appearance of A. mureroensis in both areas can be provisionally used for regional correlation until homotaxic tests are checked.