Some lower Middle Ordovician species of Asaphus (Trilobita) from Sweden

Abstract

Several Asaphus (Asaphus) species concepts are in a state of flux. Here we elucidate the morphological differences and stratigraphical occurrences of Asaphus raniceps and A. lamanskii. It is shown that Asaphus raniceps and A. ‘raniceps’ of several authors include specimens of A. raniceps, A. lamanskii, A. striatus, A. vicarius and A. fallax. Specimens of the latter have commonly been labelled A. expansus. Angelin's ‘A. acuminatus’ is interpreted as a species distinct from Boeck's A. acuminatus. The dorsal pattern of terrace lines is described and used in species discrimination. The number of axial rings in the anterior half of the pygidium is a second new character useful in characterising and identifying Asaphus species. Diagnoses and descriptions are provided for A. raniceps, A. lamanskii, A. vicarius and A. angelini n. sp. It is shown that both A. raniceps and A. vicarius occur in the Asaphus ‘raniceps’ Zone, and it is proposed to rename that zone to the Asaphus raniceps and Asaphus vicarius Zone.

Keywords:

• Middle Ordovician
• Kunda Stage
• biostratigraphy
• trilobite biozones
• Asaphus
• raniceps
• lamanskii
• vicarius
• angelini n.sp

Acknowledgements

The authors would like to thank Åke Bruun (SGU, Uppsala), Kent Larsson (Lund), Harry Mutvei (Stockholm), Arne T. Nielsen (Copenhagen) and David L. Bruton (Oslo) for facilitating access to material and valuable discussions. Access to the Gillberga quarry was granted by Ölandssten AB, Sandvik. Financial support of the field work through the Royal Swedish Academy of Sciences (Kungliga Vetenskapsakademien) is gratefully acknowledged. Jan-Ove R. Ebbestad (Uppsala) helped with access to literature. Two anonymous referees gave critical reviews that greatly helped to improve the quality and consistency of the text.