The shape of biodiversity through deep time: fossils vs. mechanistic models

<p>Palaeontologists have debated for over fifty years whether the fossil record is adequate to document the diversification of life. One view has been that the record is so heterogeneous that any signal would be misleading, whereas others have accepted that the fossils broadly tell the true story. The debate had reached an impasse. In our new work, published in <em>Nature</em> in July 2022, we use a mechanistic model, combining palaeogeographic maps, temperature data, and productivity data to map out biodiversity hotspots through the Phanerozoic. The model runs from the Cambrian to the present day and predicts current marine biodiversity distribution. We argue that this non-biological mechanistic model then gives an accurate plot of the trajectory of palaeobiodiversity and in fact confirms that the fossil record retains a strong signal of reality.</p><p>&#160;&#160;&#160;&#160;&#160;&#160; Two key outcomes of the analysis include an explanation for why life is so diverse today, especially in tropical oceans, and the observation that marine biodiversity never approached equilibrium and indeed is better modelled as an exponential process rather than a logistic/ equilibrium process. First, the five-fold increase in palaeodiversity through the Mesozoic and Cenozoic can be explained by Vermeij&#8217;s Mesozoic Marine Revolution, a biological model that focuses on innovation, but also, we suggest, by the long-term stability of biodiversity hotspots since the Triassic and Jurassic. Second, the continuing rise in palaeodiversity from the Triassic to the present day appears to be real, and our model fitting, involving massive iteration to model all kinds of uncertainties, shows that the calibrated logistic model is the best even though marine invertebrate diversity in most of the ocean operates within the exponential growth regime. The calibrated model shows that in tropical biodiversity hotspots, diversity begins to approach equilibrium. Further, our tests show that marine life worldwide never approached saturation, in fact remaining at about 25% of plenitude. This opens up many new ideas about how to comprehend a world of exponentially increasing marine biodiversity.</p>