Patterns of bryozoan endemism through the Ordovician–Silurian transition

Abstract

Area cladograms produced by parsimony analysis of endemicity illustrate historically developed biogeographical associations among Caradocian, Ashgillian, Llandoverian, and Wenlockian bryozoans. Areas in North America, Siberia, and Baltica were organized into three provinces and 12 biomes over a time interval of 35 million years. Six of these biomes belonged to the North American-Siberian Province and became extinct during the Ashgillian. Three biomes represent a successional series of biogeographical associations in the Late Ordovician of Baltica, and the middle biome of this succession is most closely related to that of the Wenlockian platform in North America. All four Silurian biomes are represented in Late Ordovician local areas, indicating that the associations important in the recovery radiation were already in existence prior to the extinction events. Three of these four biomes expanded their geographic extent in the wake of the Late Ordovician extinctions. Several biome extinction and replacement events took place during lowstands of sea level, suggesting that biogeographic reorganizations took place as a consequence of habitat loss in epeiric seas. Biome development largely depended on the extent of major litho-topes and their intersections with deep ocean and climatic barriers. The loss of regional habitats, associated with marine regression, was a key factor in biome extinction and reorganization, and indicates that biogeography played a significant role in the Late Ordovician mass extinctions and Silurian recovery radiations. Vicariance hypotheses are needed to account for the development of barriers subdividing ancestral areas, whereas hypotheses of congruent dispersal are required to explain the appearance of biomes in geographically disjunct areas.

Upper Ordovician Bryozoans of the Pin Formation (Spiti Valley, Northern India)

“…Besides the cosmopolitan species Kukersella borealis (Bassler, 1911 b ), both Indian and South European localities share genera like Lichenalia , Stellatodictya and Ralfina (Ernst and Key, in press). The South European Plate was very close to the Baltic region; hence, it is included within the North Estonia II Biome (Anstey et al . 2003).…”

Late Ordovician (Sandbian) bryozoans and their depositional environment, Furuberget Formation, Mjøsa District, Oslo Region, Norway

“…The Furuberget Formation faunas are completely different from those in the overlying unit (the Mjøsa Formation) and only one genus is shared (Eridotrypa) (Ernst & Nakrem, in press). The biogeography of Late Ordovician bryozoans has been discussed in Ross (1985), Tuckey (1990), Anstey et al (2003), Jiménez-Sánchez (2009), Kácha & Šarič (2009), Jiménez-Sánchez & Villas (2010, Taylor & Sendino (2010) and briefly in Ernst & Nakrem (in press). On species level the Furuberget Formation bryozoan fauna resembles very much time equivalent units in the Baltic province, as well as North American (Laurentian) faunas.…”

“…All species are new additions for the Norwegian Ordovician to the bryozoan database used by e.g. Anstey et al (2003) and Jiménez-Sánchez & Villas (2010).…”

Endemism in historical biogeography and conservation biology: concepts and implications

“…The units used in PAE are predetermined areas of any kind, such as arbitrary operational units (van Soest, 1994), quadrats (Morrone 1994a, Linder 2001a,b, García-Barros et al 2002, Morrone and Escalante 2002, Rovito et al 2004, García-Barros, 2003, Rojas-Soto et al 2003, Vergara et al 2006, Herrera-Paniagua et al 2008, Meng et al 2008, Löwenberg-Neto and de Carvalho, 2009, Ramírez-Barahona et al 2009), islands (Bisconti et al 2001, Trejo-Torres and Ackerman 2001, Fattorini 2002, localities (Raxworthy and Nussbaum, 1996, Ron 2000, Anstey et al 2003, Ribichich, 2005, Ramírez-Arriaga and Martínez-Hernández, 2007, Gates et al 2010, Aguirre et al 2011, interfluvial regions (Silva and Oren 1996), hydrological basins (Aguilar-Aguilar et al 2003, Huidobro et al 2006, politically defined areas (Cué-Bär et al 2006, Nelson 2008, Ribeiro and Eterovic 2011, biogeographical areas (Glasby andAlvarez 1999, Vega et al 1999), predefined areas of endemism (Goldani et al 2002, Katinas et al 2004, Espinosa et al 2006, Albert and Carvalho 2011. In a few analyses, latitudinal (Morrone et al 1997…”