ALBERT

Description: Strata of the Solvik Formation in the central Oslo Region (upper Hirnantian through most of Aeronian) are very fossiliferous and provide a good record relating to the survival and recovery faunas after the end-Ordovician mass extinctions. The ribbed atrypide fauna is especially rich with 21 species present. Samples from most of these taxa have been sectioned to reveal internal structures for taxonomic study. Of these, 13 species belong to the family Atrypidae, three of which are described in the present paper; Dihelictera engerensis n. sp., Gotatrypa vettrensis n. sp., and Rhinatrypa henningsmoeni n. gen. The family Atrypidae follows a global pattern of recovery with an increase in diversity registered in upper Rhuddanian and further diversification in Aeronian strata. The focus of this paper is the family Atrypinidae, which shows a different pattern. They are common and fairly diverse near the base of the Rhuddanian in deeper waters and rare further up, especially in the Aeronian. One new genus, Bockeliena, and two new species, Plectatrypa rindi and Euroatrypa? sigridi are defined. The relationship between the subfamilies Spirigerininae and Plectatrypinae is clarified through thin sections of material from the Ordovician/Silurian boundary layers. The plectatrypids originated in Baltica through transitional species found in upper Katian to Hirnantian strata leading from the cosmopolitan Eospirigerina to the Plectatrypa lineage with imbricate ribbing and, separately, to Bockeliena and others with lamellose, widely spaced ornamentation. The Oslo Region probably acted as a nexus for survival and spread of brachiopods after the end-Ordovician mass extinction. UUID: http://zoobank.org/95340b41-5537-4192-9338-211a2940bea8.

Description: Strata of the Solvik Formation in the central Oslo region (upper Hirnantian to upper Aeronian) are rich in atrypides that elucidate the evolution of this group. A few athyridide brachiopods are also present. Eleven taxa of smooth spire-bearers are described taxonomically using fossils and peels. Among these occur one new genus, Eisaella, and five new species: Eisaella uniplicata, Thulatrypa huangi, T. vikenensis, ?Becscia pentagona, and Shelvothyris bivittata. Atrypides make up 30% (24 genera) of the total brachiopod genera in the Solvik Formation, more than one third of the known global atrypide fauna during that interval. Most are members of the family Lissatrypidae, illustrating the evolution of this group from upper Hirnantian and lower Silurian strata. These show close affinity to each other attesting to ongoing radiation. The new genus Eisaella is a likely ancestor of Lissatrypa, while Meifodia displays a gradual evolution through the formation. Atrypides were most diverse at the base and top of the Solvik Formation due to heterogony in environments and water depth, but were less diverse in the comparatively constant environmental setting of the late Rhuddanian time. The basal assemblages with few atrypides from shallow facies may be compared to the shallow Cathay Fauna of China. Most of the abundant Norwegian atrypide fauna is found in deeper water with few comparable faunas known globally. The Oslo region may have served as a center for the evolution and spread of atrypides immediately following the end-Ordovician glacial drawdown in sea level. UUID: http://zoobank.org/508dba95-5501-403d-9a4d-deeb324847c9