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.

Data processing steps are detailed in the Methods section of the paper.

Occurrence data were downloaded from the Paleobiology Database (www.paleobiodb.org). Paleobiology Database are licensed under a CC BY 4.0 International License <https://creativecommons.org/licenses/by/4.0/>, 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