Silurian-Devonian boundary events and their influence on cephalopod evolution: evolutionary significance of cephalopod egg size during mass extinctions

Abstract

Diversity evolution of 197 of the latest Ludlow-Lochkovian cephalopod species from Bohemia (representing more that 70 percent of all species known worldwide) was analysed and compared with changes in the global carbon cycle in the marine ecosystem. Our results show a distinct relationship between cephalopod species diversity and the global carbon cycle. A progressive increase in δ 13 C values in marine carbonates from the Monograptus lochkoviensis Zone to the end of the Monograptus transgrediens Zone reflects an increase of bioproductivity in the marine ecosystem. This increase was probably caused by a shallowing of the upwelling system, thus importing nutrient-rich water. A progressive cooling during the Přídolí and earliest Lochkovian triggered these changes in the upwelling system. Our data also show an increase in total diversity of cephalopod species, which may be explained by greater availability of new food sources for a period corresponding to the progressive increase in δ 13 C values. In the latest Silurian, δ 13 C reached its maximal values while the Lochkovian is characterized by steady conditions with a decreasing tendency in δ 13 C values. Strong, selective extinction started in the latest Silurian Monograptus transgrediens Zone and continued to the earliest Devonian Monograptus uniformis Zone. This extinction affected benthic and demersal cephalopod species with relatively large eggs and long incubation times. The change in dynamics of the global carbon cycle thus coincides with the beginning of this extinction. An anoxic or hypoxic event in the period between the LAD Monograptus transgrediens Zone (Transgrediens Event) in the latest Přídolí and the base of the Devonian Monograptus uniformis Zone (documented also from offshore sequences from Poland) is considered to be a cause for the extinction of non-pelagic cephalopods. Our study also revealed a need to revise and define all earlier established bioevents in the Silurian-Devonian boundary interval more clearly. •

Silurian carcinosomatid eurypterids from the Prague Basin (Czech Republic)

“…This occurrence is consistent with the dispersion pattern of many other invertebrate groups; e.g. nautiloid cephalopods (Gnoli 2003;Manda 2008;Manda & Frýda 2010;Turek & Manda 2011Histon 2012a, b), shallow-water bivalve communities (Kříž 2008, Cope & Kříž 2013) and inarticulate brachiopods (Mergl 2006(Mergl , 2010. We suggest that carcinosomatids had a more nektic lifestyle whereas pterygotids were more demersal, possibly explaining the replacement of a carcinosomatid fauna in the Wenlock by a pterygotid fauna in the Ludlow and Přídolí.…”

Unusual occurrence of dalmanitid trilobites in the Lochkovian of the Prague Basin (Czech Republic)

“…This migration route (A in Fig. 6) is consistent with the suggested course of the South Equatorial Current (sensu Wilde 1991) as well as the South Tropical Current along the NE margin of Laurussia (see Scotese & McKerrow 1990, Gnoli 1985, Gnoli et al 1988, Manda & Frýda 2010, Frey et al 2014. In the latest Lochkovian there was another, minor influx of new trilobite elements -e.g.…”

A long-lasting steady period of isotopically heavy carbon in the late Silurian ocean: evolution of the δ13 record and its significance for an integrated δ13, graptolite and conodont stratigraphy

“…The rich cephalopod fauna of this bed had already been studied by Barrande (1865Barrande ( -1877 and elements of several cephalopod lineages are described from this level (Turek 1975(Turek , 1976Kříž et al 1986;Kříž 1998b;Manda & Turek 2009;Manda & Frýda 2010).…”