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Keywords:

  • Functional morphology;
  • Middle Ordovician;
  • pelagic trilobite;
  • Telephina

Well preserved parts of Telephina bicuspis described from dark limestone concretions of Llanvirn age, in the Oslo Region, Norway, exhibit many features associated with a pelagic life style for this trilobite. The free cheek has a huge holochroal eye with perfectly square lenses and a long genal spine which is unique in being directed vertically upwards rather than ventrally. Additional spines include an occipital spine, the macro spine on the rachis of the 6th thoracic segment and paired spines from each of the two rachial rings of the pygidium. These spines may have had a hydrodynamic and stabilizing function. The genal spine could have had a sensory function or been a dimorphic feature. The hypostoma is figured for the first time and a reconstruction is given for the complete exoskeleton.