Acta Palaeontologica Polonica

Revision of the late Ordovician trilobite Holotrachelus punctillosus (Törnquist, 1884) from Dalarna, Sweden

Yutaro Suzuki

Acta Palaeontologica Polonica 46 (3), 2001: 331-348

Holotrachelus punctillosus from the Boda Limestone (Ashgill, Upper Ordovician) of Sweden is redescribed. The systematic position of this problematic species is discussed. Its distinctive morphology appears to be the result of an adaptation towards illaenid life habits. The pygidial morphology, with the extra-fulcral field developed as segmental pleural spines, makes an assignment possible to only four Ordovician groups, namely the Remopleuridioidea, Odontopleuroidea, Lichoidea and Cheiruroidea. Of these, the former three are so different that a direct affiliation is out of the question. Similarities with the Cheiruroidea are the more persuasive, particularly after a misinterpretation of the facial suture is corrected and some other problems are sorted out. It is suggested that the Holotrachelinae are placed within the Cheiruridae, where it may have special affinities to the Sphaerexochinae.

Key words: Trilobita, Holotrachelus, Proetida, Cheiruridae, Sphaerexochinae, Ordovician, Sweden.

Yutaro Suzuki [], National Science Museum, Japan. 3-23-1 hyakunincho, shinjuku-ku Tokyo, 169-0073 Japan.

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