Marine Ecosystem Structure and Function from the Late Cretaceous to the Pliocene: Investigating the Origins of Modern Marine Communities

The origins of modern marine community structure and function remain incompletely understood. Major mass extinction events, particularly the Cretaceous-Palaeogene (K-Pg, ~66 Ma), profoundly reshaped the composition and taxonomic identities of marine ecosystems. The following Cenozoic Era experienced pronounced climatic variability, from hyperthermal to hypothermal episodes and a long-term cooling trend from the Oligocene onward. These climatic transitions coincided with faunal turnover and the diversification of modern clades, along with shifts in community composition, biogeographic patterns, and benthic dominance, all of which contributed to the establishment of modern marine ecosystems. However, it remains unclear how the K-Pg extinction and Cenozoic climate extremes influenced the development of modern marine community structure and function, whether this ‘modernisation’ occurred gradually or through punctuated events, as well if and how a functional diversity gradient (LFDG) emerged in relation to the well-documented latitudinal species diversity gradient (LDG).
This thesis addresses these gaps through two studies with three overarching aims: (1) to assess changes in trophic structure across the K-Pg extinction and subsequent recovery interval; (2) to investigate global patterns of marine invertebrate functional diversity from the Late Cretaceous to the Pliocene; and (3) to examine the development of a latitudinal functional diversity gradient over this interval, all to identify the origins of modern marine community organisation.
The findings demonstrate that Antarctic trophic meta-webs experienced only short-term disruption at the K-Pg boundary, with no lasting structural or functional reorganisation. Likewise, global marine invertebrate functional diversity exhibited no directional trend from the Late Cretaceous to the Pliocene and did not decline in association with the K-Pg extinction event. Functional diversity was persistently highest in palaeotemperate regions, and remained decoupled from taxonomic diversity, which shifted from a palaeotemperate peak in the Cretaceous to a tropical maximum by the Late Pliocene. Together, these results indicate the functional structure of marine ecosystems has been comparatively stable over the last 70 Myr, and that the establishment of the modern latitudinal taxonomic diversity gradient apparently occurred independently of changes in functional diversity.