The apparent exponential radiation of Phanerozoic land vertebrates is an artefact of spatial sampling biases

There is no consensus about how terrestrial biodiversity was assembled through deep time, and in particular whether it has risen exponentially over the Phanerozoic. Using a database of 38,711 fossil occurrences, we show that the spatial extent of the ‘global’ terrestrial tetrapod fossil record itself expands exponentially through the Phanerozoic, and that this spatial variation explains around 75% of the variation in known fossil species counts. Controlling for this bias, we find that regional-scale terrestrial tetrapod diversity was constrained over timespans of tens to hundreds of millions of years, and similar patterns are recovered for major subgroups, such as dinosaurs, mammals and squamates. The Cretaceous/Paleogene mass extinction, 66 million years ago, fundamentally disrupted terrestrial ecosystems, catalysing an abrupt increase in its aftermath. Nevertheless, this was followed by general stasis and recent diversity levels do not exceed those of the Paleogene. These findings parallel those recovered in analyses of local community-level richness, suggesting that tetrapod beta diversity has also not shown a general increase through time. Taken together, our findings strongly contradict past studies that suggested unbounded diversity increases over the last 100 million years.
Methods
Data processing steps are detailed in the Methods section of the paper.