Article: The tergomyan mollusc Carcassonnella from the Upper Ordovician of Girvan, Scotland
Jan Ove R. Ebbestad
The tergomyan genus CarcassonnellaHorný and Peel, 1996 is common in and characteristic of the Mediterranean Province in peri-Gondwanan terranes during the late Tremadoc and Arenig. It is united with other small, slit-bearing cyrtonellids in the Carcassonnellidae Horný, 1997b, of which BaltiscanellaHorný, 1997b from the Arenig of the Oslo Region, Norway, and Sarkanella from the Caradoc of the Siljan District, Sweden has been recognized outside the Mediterranean Province. The most inclusive view of the Carcassonnellidae unites PeelerophonYochelson, 1982, CarcassonnellaHorný and Peel, 1996, SarkanellaHorný, 1997a, BaltiscanellaHorný, 1997b, and TachillanellaHorný, 1997b. Patterns of distribution of genera in the family are obscured, however, by widely different phylogenetic relationships presented in the literature. Here, Carcassonnella multilineata (Reed, 1920) is documented in the upper Whitehouse and Drummuck subgroups of the Girvan district, Midland Valley of Scotland, being the first record of the genus outside peri-Gondwana. Its enigmatic occurrence on the edge of Laurentia is opposed to the occurrence of low latitude benthic faunas in higher latitudes during this time interval (the Boda Event). It is likely, therefore, that the genus spread from the ancient stock found on the Perunican microcontinent as this drifted away from Gondwana in the mid-Caradoc.