A newly discovered, diverse sponge fauna of early Silurian age, is described from Gotland, Sweden. This is the first Silurian sponge assemblage known from Baltica, and the only diverse Llandoverian assemblage known worldwide. The fauna includes 20 genera and 29 species, of which three genera and six species are new. Eighteen species are new to Baltica. The fauna shows strong similarities to later Silurian assemblages in Arctic Canada, but one endemic species comprises ca. 50% of the fauna. The fauna shows that lithistid sponges recovered well from the late Ordovician extinction in some areas, and became widely spread in the early Silurian. In contrast, non-lithistid sponges like, such as hexactinellids, appear to have evolved rapidly during the Late Ordovician early Silurian interval, and some modern groups probably originated in inshore habitats.
Introduction 1
Institutional abbreviations 3
Geological setting 3
Material, methods, terminology 6
Systematic palaeontology 8
Phylum Porifera Grant, 1836 8
Class Demospongea Sollas, 1875 8
Order Orchocladina Rauff , 1895 8
Family Anthaspidellida Miller, 1889 8
Genus Archaeoscyphia Hinde, 1889 8
Archaeoscyphia minganensis Billings, 1859 8
Archaeoscyphia annulata Rigby, 1973 12
Archaeoscyphia gislei de Freitas, 1989 14
Archaeoscyphia rectilinearis de Freitas, 1989 16
Archaeoscyphia aulocopiformis de Freitas, 1989 18
Archaeoscyphia scalaria de Freitas, 1989 19
Archaeoscyphia attenuata de Freitas, 1989 21
Genus Finksella Rigby& Dixon, 1979 22
Finksella turbinata Rigby& Dixon, 1979 22
Genus Calycocoelia Bassler, 1927 24
Calycocoelia typicalis Bassler, 1927 24
Genus Climacospongia Hinde, 1884 25
Climacospongia undulata de Freitas, 1991 26
Genus Multistella Finks, 1960 28
Multistella leipnitzae nsp 29
Genus Somersetella Rigby& Dixon, 1979 32
Somersetella amplia Rigby& Chatterton, 1989 32
Somersetella digitata Rigby& Dixon, 1979 34
Family Streptosolenidae Johns, 1994 35
Genus Postperissocoelia ngen 35
Postperissocoelia gnisvardensis nsp 36
Family Chiastoclonellidae Rauff , 1895 38
Genus Chiastoclonella Rauff , 1895 39
Chiastoclonella spRauff , 1895 39
Subclass Tetractinomorpha Lévi, 1953 39
Order Streptosclerophorida Dendy, 1924 39
Suborder Eutaxicladina Rauff , 1894 39
Family Hindiidae Rauff , 1893 39
Genus Hindia Duncan, 1879 40
Hindia sphaeroidalis Duncan, 1879 40
Suborder Sphaerocladina Schrammen, 1910 42
Family Astylospongiidae Zittel, 1877 42
Genus Caryoconus Rhebergen& van Kempen, 2002 42
Caryoconus gothlandicus (Schlüter, 1884) 42
Genus Lindstroemispongia ngen 45
Lindstroemispongia cylindrata nsp 47
Order Spirosclerophorida Reid, 1963 48
Suborder Rhizomorina Zittel, 1878a 48
Family Haplistiidae de Laubenfels, 1955 48
Genus Haplistion Young& Young, 1877 48
Haplistion minutum Rigby& Dixon, 1979 50
Haplistion cylindricum Rigby& Dixon, 1979 52
Haplistion toftanum nsp 54
Haplistion spYoung& Young, 1877 57
Genus Warrigalia Rigby& Webby, 1988 59
Warrigalia robusta Rigby& Webby, 1988 59
Rhizomorina indet 62
Subclass Tetractininellida? Marshall, 1876 62
Order Hadromerida? Topsent, 1898 63
Family uncertain 63
Genus Opetionella von Zittel, 1878 63
Opetionella incompta nsp 63
Class Hexactinellida Schmidt, 1870 65
Order Lyssacinosida? von Zittel, 1877 65
Family uncertain 65
Genus Urphaenomenospongia ngen 65
Urphaenomenospongia euplectelloides nsp 66
Lyssacinosida? indet 69
Order and family uncertain 71
Hexactinellid indetA 71
Hexactinellid indetB 71
Spiculite 72
Class Stromatoporoidea Stearn, Webby, Nestor& Stock, 1999 74
Order Labechiida Kühn, 1927 74
Family Stylostromatidae Webby, 1993 74
Genus Pachystylostroma Nestor, 1964 74
Pachystylostroma sp 74
Order Clathrodictyida Bogoyavlenskaya, 1969 76
Family Clathrodictyidae Kühn, 1939 76
Genus Clathrodictyon Nicholson& Murie, 1878 76
Clathrodictyon sp 76
Order Stromatoporida Stearn, 1980 76
Family Syringostromellidae Stearn, 1980 76
Genus Syringostromella Nestor, 1966 76
Syringostromella sp 76
Order Amphiporida Rukhin, 1938 76
Family Amphiporidae Rukhin, 1938 76
Genus Amphipora Schulz, 1883 76
Amphipora sp 76
Palaeobiogeography and community evolution 77
Taphonomy 80
Palaeoecology and palaeoenvironmental interpretation 80
Conclusions 83
Acknowledgements 83
References 83
