The Ordovician sponge Palaeomanon cratera (Roemer, 1848) as an erratic on Gotland (Sweden)

摘要

Recent cataloguing of collections of Late Ordovician erratic sponges from Gotland (Sweden) in Swedish museums has revealed the presence of Palaeomanon cratera (Roemer, 1848), previously known only from Silurian strata in Tennessee (USA) and the Northwest Territories (Canada). The species forms part of a rich sponge assemblage occurring on Gotland, representing one of three associations in north and northwest Europe, and originating from unknown source areas in Baltica. Palynomorphs extracted from adhering sediment document a Late Ordovician (Ashgill) age; thus, they are the oldest representatives of the species known to date. Naturally, this has implications for the palaeobiogeography of Palaeomanon, in relation to faunal exchange between Baltica and Laurentia; a possible migration from Baltica to Laurentia is discussed.