Agnathan vertebrates in the Lower Silurian of Gotland, Sweden

Abstract

Abstract The vertebrate scale collections from the Telychian? (upper Llandovery) Lower Visby Beds to the Gorstian? (lower Ludlow) upper Klinteberg Beds mostly represent low diversity thelodont faunas. In the oldest part, the Lower Visby Beds, only one scale of each of the thelodont genera Loganellia and Thelodus has been found. Scales were absent in samples from the Upper Visby Beds and throughout to the Slite Beds, unit f, where Loganellia grossi n. sp. occurs. This species occurs throughout the Slite Beds together with Thelodus schmidti, and, occasionally, with the anaspid Birkeniida sp. D, and the osteostracans Oeselaspis sp. and Procephalaspis oeselensis?. In the upper Homerian Halla Beds L. grossi n. sp. has been replaced by L. martinssoni. T. schmidti and L. martinssoni occur together with fragments of a third osteostracan, Tremataspis sp., and with Birkeniida sp. D, and Birkeniida sp. in the lower part of the Halla Beds, unit b, at Möllbos 1. In the upper half of the Möllbos 1 sections a spiny variant of T. schmidti occurs. This variant has so far only been found at this single locality. L. martinssoni and T. schmidti are the only vertebrates found in the remaining parts of the Halla, Mulde, and Klinteberg Beds, apart from the high diversity fauna in Halla Beds, unit c, at Gothemshammar, where both anaspids and the osteostracans Oeselaspis sp., Procephalaspis oeselensis?, Tremataspis sp., and Osteostraci gen. et sp. indet. have been found.