The trilobite Tretaspis at the Middle-Upper Ordovician boundary in Västergötland

Abstract

The trinucleid trilobite Tretaspis was a late Caradoc immigrant from North America into Scandinavia and the Anglo-Welsh area. The earliest species in both areas was T. ceriodes Angelin. Taxonomic problems surrounding the nominate subspecies from Kinnekulle are resolved by the selection of a lectotype. A new species, T. percontator sp. nov., from Gullhögen quarry is described. It was almost certainly derived from T. ceriodes ceriodes and provides a link between the T. moeldenensis and T. seticornis species groups. A stratigraphical position close to the Caradoc-Ashgill boundary (= lowest Harjuan) is suggested for the calcareous mudstone containing T. percontator.

Key Words:

• Trilobita
• Trinucleidae
• Tretaspis
• taxonomy
• evolution
• Middle-Upper Ordovician boundary
• Kinnekulle
• Gullhögen quarry
• Västergötland
• Sweden