The cephalopods of the Kullsberg Limestone Formation, Upper Ordovician, central Sweden and the effects of reef diversification on cephalopod diversity

Abstract

The cephalopods collected from the mud-mounds of the Kullsberg Limestone Formation, late Sandbian-earliest Katian(?), south central Sweden, are highly diverse and comprise 26 identifiable species of 12 families and six orders in a sample of c. 180 specimens. The assemblage is strongly dominated by orthocerids in abundance and diversity. In contrast, the time equivalent assemblage of the reef limestone of the Vasalemma Formation of Estonia is dominated by actinocerids and less diverse. Only one third of the species co-occur in the two palaeogeographically relatively close assemblages, respectively. The taxonomic composition of the Kullsberg assemblage is on the order level more similar to that of the late Katian-early Hirnantian Boda Limestone Formation of south central Sweden, which represents a similar relatively deep depositional environment. The high local differentiation of cephalopod reef faunas exemplifies the importance of the emergent Baltic reef habitats in the diversification processes during early Late Ordovician. Of the described taxa, the following are new:

Impacts of spatial and environmental differentiation on early Palaeozoic marine biodiversity

“…One 11 mechanism for increasingly close spatial packing of taxa is the rise of environmental spatial heterogeneity at increasingly small scales, for example through the expansion of complex environments such as reefs. This creates ever-smaller environmental niches for species to occupy, increasing niche packing and consequently α diversity 1,39 . According to this model, taxa cannot persist in environments where they are outcompeted in all niches; the more specialised the niche, the less likely it is that an individual will find its niche when colonising a new area.…”

The diploporite blastozoan Glyptosphaerites (Echinodermata: Blastozoa) and the origin of diplopores

“…Other species. Glyptosphaerites suecica Angelin, 1878, from the 'Lower Chasmops Limestone' of Dalarna, Sweden, which corresponds to the Lower Kullsberg Limestone and is of Upper Sandbian to Lower Katian age (Kröger & Aubrechtová 2019). Regnéll (1945, p. 157) doubted its validity, but accepted it was distinctly younger than G. leuchtenbergi.…”