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.

目前学界对于陆地生物多样性如何随地质深时演替尚未达成共识，尤其是显生宙（Phanerozoic）期间其多样性是否呈指数增长态势。本研究依托包含38711条化石产出记录的数据集，证实“全球”陆地四足动物（tetrapod）化石记录的空间分布范围在显生宙期间呈指数扩张，且该空间分布差异可解释约75%的已知化石物种数量波动。在控制该采样偏差后，研究发现区域尺度的陆地四足动物多样性在数千万至数亿年的时间跨度上始终受到约束，该模式在恐龙、哺乳动物、有鳞类等主要类群中均得到验证。6600万年前的白垩纪/古近纪（Cretaceous/Paleogene）集群灭绝事件彻底重塑了陆地生态系统，在事件后催生了多样性的骤然跃升。但在此之后，陆地四足动物多样性整体趋于停滞，当前的多样性水平并未超出古近纪时期。本研究结果与基于局域群落物种丰富度的分析结论高度一致，表明四足动物的β多样性（beta diversity）也未随时间呈现普遍上升趋势。综上，本研究结论与此前认为过去1亿年间陆地生物多样性无上限增长的多项研究存在显著矛盾。