Key stages in the evolution of the Antarctic marine fauna

Abstract

We are beginning to appreciate that the origin of the modern Antarctic marine fauna is related to a series of key events throughout the Cenozoic era. In the first of these, the mass extinction at the Cretaceous–Palaeogene boundary (66 Ma) reset the evolutionary stage and led to a major radiation of modern taxa in the benthic realm. Although this took place in a greenhouse world, there is evidence to suggest that the radiation was tempered by the seasonality of primary productivity, and this may be a time‐invariant feature of the polar regions. Although there could well have been a single, abrupt extinction event at c. 34 Ma, there is also evidence to suggest a phased extinction of various taxa over a period of millions of years. Important new molecular phylogenetic data are indicating that a wide variety of both benthic and pelagic taxa radiated shortly after a second major phase of cooling at c. 14 Ma. Such a phenomenon is linked to a series of major palaeoceanographic changes, which in turn led to a proliferation of diatom‐based ecosystems. Although the modern benthic marine fauna can be traced back some 45–50 Myr, a substantial component of the modern pelagic one may be less than 14 Myr old. The latter is also characterized by assemblages of high abundance but comparatively low species richness and evenness. A distinctive signature of low diversity but high dominance within Antarctic marine assemblages was maintained by the interplay between temperature and primary productivity throughout the Cenozoic.

Species richness and turnover among indigenous and introduced plants and insects of the Southern Ocean Islands

“…Although the patterns and processes underlying species richness variation in the region are well known (Chown et al. , Crame ), key areas remain in need of further exploration. Among these, understanding species turnover is especially important.…”

“…Despite low eukaryote diversity on the continent itself, the Southern Ocean and its isolated islands have a rich biota. Although the patterns and processes underlying species richness variation in the region are well known (Chown et al 2015, Crame 2018, key areas remain in need of further exploration. Among these, understanding species turnover is especially important.…”

Is reproductive strategy a key factor in understanding the evolutionary history of Southern Ocean Asteroidea (Echinodermata)?

“…However, isolation of the SO was reduced several times during periods of climate warming and the decreasing ACC intensity (Dalziel et al, ; Lagabrielle, Goddéris, Donnadieu, Malavieille, & Suarez, ). In a recent review of key stages in the evolution of the Antarctic marine fauna, Crame () emphasizes the influence of past climate on the current distribution of modern fauna. At the scale of the Cenozoic (c. 65 Myr), he points out that the succession of several major extinction and radiation events are linked to important drops in seawater temperature.…”

PhylSim: A New Phylogenetic Tool for Modeling Trait Evolution and Speciation

“…We simulate the change in the environmental conditions in this case by setting three different regimes. The first regime, from t = 0 to t = 12 Myrs, corresponds to a period of relatively stable temperatures in the Southern Ocean around 8 degrees Celsius, as described by Crame (2018) [5]. During this period, the simulation follows an Ornstein-Uhlenbeck process with a moderate speciation rate due to the climate conditions.…”

“…The second regime is a period of warming of the Southern Ocean, between t = 12 and t = 18 Myrs, in which the temperature increases to about 12 degrees [5]. During this time, the speciation rate is significantly reduced, and there are smaller jumps in the value of the trait in the Ornstein-Uhlenbeck process.…”