The Early Origin of the Antarctic Marine Fauna and Its Evolutionary Implications

Abstract

The extensive Late Cretaceous – Early Paleogene sedimentary succession of Seymour Island, N.E. Antarctic Peninsula offers an unparalleled opportunity to examine the evolutionary origins of a modern polar marine fauna. Some 38 modern Southern Ocean molluscan genera (26 gastropods and 12 bivalves), representing approximately 18% of the total modern benthic molluscan fauna, can now be traced back through at least part of this sequence. As noted elsewhere in the world, the balance of the molluscan fauna changes sharply across the Cretaceous – Paleogene (K/Pg) boundary, with gastropods subsequently becoming more diverse than bivalves. A major reason for this is a significant radiation of the Neogastropoda, which today forms one of the most diverse clades in the sea. Buccinoidea is the dominant neogastropod superfamily in both the Paleocene Sobral Formation (SF) (56% of neogastropod genera) and Early - Middle Eocene La Meseta Formation (LMF) (47%), with the Conoidea (25%) being prominent for the first time in the latter. This radiation of Neogastropoda is linked to a significant pulse of global warming that reached at least 65°S, and terminates abruptly in the upper LMF in an extinction event that most likely heralds the onset of global cooling. It is also possible that the marked Early Paleogene expansion of neogastropods in Antarctica is in part due to a global increase in rates of origination following the K/Pg mass extinction event. The radiation of this and other clades at ∼65°S indicates that Antarctica was not necessarily an evolutionary refugium, or sink, in the Early – Middle Eocene. Evolutionary source – sink dynamics may have been significantly different between the Paleogene greenhouse and Neogene icehouse worlds.

Persistent ecological shifts in marine molluscan assemblages across the end-Cretaceous mass extinction

“…More numerous and intense interspecific interactions are apparent from an increased proportion of predatory gastropods at two of the studied sites (Fig. 3E) and elsewhere (21,28,29) and a global diversity increase of marine metazoan predators in the wake of the mass extinction (3). Antipredatory behavior is also evident as an escape strategy in motile organisms and as an avoidance strategy in those that burrowed into the sediment, whereas morphological adaptations showed little effects at the KPB (52).…”

“…Increased predation pressure after the KPB has been inferred from the radiation of predatory carnivores, in particular neogastopods (3,18,21,(26)(27)(28), elevated gastropod drilling frequencies (29,30), and a trend toward deeper burrowing in bivalves (31), but predatory Significance Global change and regime shifts of ecosystems are a major concern today. It has been suggested that the end-Cretaceous impact of an asteroid not only caused mass extinction but also involved the transgression of a global tipping point.…”

Differentiation of high‐latitude and polar marine faunas in a greenhouse world

“…None of the eight Late Maastrichtian species can be referred to extant genera, and only one of them crosses the K-Pg boundary. Both the increases in numbers of species and the proportion of modern genera up section are statistically significant (Crame et al, 2014). 3).…”

“…The Antarctic and two tropical localities all show clear indications that the richness of Early Cenozoic neogastropods peaked during the Middle Eocene (Crame et al, 2014;Dockery & Lozouet, 2003;Huyghe, Lartaud, Emmanuel, Merle, & Renard, 2015; Supporting Information Figures S1-S3). Nevertheless, levels of dissimilarity between all three localities in the Palaeocene are already extremely high, as there are no genera in common between the Paris Basin (42 genera) and Antarctica (19 genera), and only one between the U.S. Gulf Coast (45 genera) and Antarctica (Table 1; Appendix).…”

“…This is particularly so in Antarctica, where intensive investigation of the prolific La Meseta Formation of Seymour Island, Antarctic Peninsula (c. 658 S palaeolatitude) has revealed that c. 32% of the Middle Eocene molluscan fauna (147 species) can be assigned to modern Antarctic and sub-Antarctic genera (Beu, 2009;Crame et al, 2014). This is particularly so in Antarctica, where intensive investigation of the prolific La Meseta Formation of Seymour Island, Antarctic Peninsula (c. 658 S palaeolatitude) has revealed that c. 32% of the Middle Eocene molluscan fauna (147 species) can be assigned to modern Antarctic and sub-Antarctic genera (Beu, 2009;Crame et al, 2014).…”