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.

Usage Notes

Occurrence data were downloaded from the Paleobiology Database (www.paleobiodb.org). Paleobiology Database are licensed under a CC BY 4.0 International License , but permission was received to archive this subset of data in Dryad under CC0 terms. For any subsequent use of this data, please also attribute the Paleobiology Database and the authors of the original records. The URLs for the downloads are all included in the dataset as text files, which are listed below. Aves_URL.txt Cetacea_URL.txt Chiroptera_URL.txt Dinosauromorpha^Aves_URL.txt Ichthyosauromorpha_URL.txt Lissamphibia_URL.txt Mosasauria_URL.txt Pinnipedimorpha_URL.txt Probainognathia^Chiroptera_URL.txt Pseudosuchia_URL.txt Pterosauromorpha_URL.txt Sauropterygia_URL.txt Sirenia_URL.txt Squamata_URL.txt Testudinata_URL.txt Tetrapoda_coll_URL.txt Tetrapoda^Aves^Chiroptera^Pterosauromorpha_URL.txt Thalattosuchia_URL.txt