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

关于地表生物多样性在漫长地质时期中的形成过程，学界尚未达成共识，特别是关于其在显生宙时期是否呈现指数增长的争论。本研究利用包含38,711个化石出现事件的数据库，揭示了‘全球’地表四足动物化石记录的空间范围在显生宙时期本身呈现指数级扩张，并且这种空间变异性解释了已知化石物种数量变化的约75%。在控制这一偏差后，我们发现区域尺度的地表四足动物多样性在数亿年的时间跨度内受到限制，对于诸如恐龙、哺乳动物和鳞蜥等主要亚群，也观察到相似的分布模式。约6600万年前的白垩纪-第三纪大灭绝事件，从根本上扰乱了地表生态系统，催化了其后急剧的增长。然而，这随后被普遍的稳定状态所继替，而最近的多样性水平并未超过古近纪时期。这些发现与局部群落丰富度分析中得出的结果相呼应，表明四足动物的β多样性也没有在时间上呈现出普遍的增加。综合来看，我们的研究结果与过去一些研究提出在过去的1亿年中无限制多样性增加的观点形成鲜明对比。