Abstract
The Carboniferous and early Permian were critical intervals in the diversification of early four-limbed vertebrates (tetrapods), yet the major patterns of diversity and biogeography during this time remain unresolved. Previous estimates suggest that global tetrapod diversity rose continuously across this interval and that habitat fragmentation following the ‘Carboniferous rainforest collapse’ (CRC) drove increased endemism among communities. However, previous work failed to adequately account for spatial and temporal biases in sampling. Here, we reassess early tetrapod diversity and biogeography with a new global species-level dataset using sampling standardization and network biogeography methods. Our results support a tight relationship between observed richness and sampling, particularly during the Carboniferous. We found that subsampled species richness initially increased into the late Carboniferous, then decreased substantially across the Carboniferous/Permian boundary before slowly recovering in the early Permian. Our analysis of biogeography does not support the hypothesis that the CRC drove endemism; instead, we found evidence for increased cosmopolitanism in the early Permian. While a changing environment may have played a role in reducing diversity in the earliest Permian, our results suggest that the CRC was followed by increased global connectivity between communities, possibly reflecting both reduced barriers to dispersal and the diversification of amniotes.
Highlights
Tetrapods first appeared on land in the late Devonian [1,2], and during the Carboniferous and early Permian established the first terrestrial vertebrate communities
This ‘rainforest collapse’ culminated in what is considered one of two mass extinction events evident in the plant fossil record [10]. Despite this interval being a crucial time for tetrapod evolution and the establishment of terrestrial ecosystems, few studies have focused on Carboniferous–early Permian tetrapod diversity patterns or have attempted to quantify the impact of the ‘Carboniferous rainforest collapse’ (CRC) on the terrestrial vertebrate fauna
Despite recent concerted attempts to close the gaps in our knowledge of early tetrapod diversity [3,50], tetrapod data for the Carboniferous and early Permian are still lacking
Summary
Tetrapods (four-limbed vertebrates) first appeared on land in the late Devonian [1,2], and during the Carboniferous and early Permian established the first terrestrial vertebrate communities. 303–307 Ma), these rainforests began to disappear from large parts of the globe, and by the early Permian had been replaced in many regions by dryland vegetation as a more arid climate developed [8,9] This ‘rainforest collapse’ culminated in what is considered one of two mass extinction events evident in the plant fossil record [10]. Despite this interval being a crucial time for tetrapod evolution and the establishment of terrestrial ecosystems, few studies have focused on Carboniferous–early Permian tetrapod diversity patterns or have attempted to quantify the impact of the ‘Carboniferous rainforest collapse’ (CRC) on the terrestrial vertebrate fauna. Using a newly compiled global species-level dataset alongside sampling standardization and network biogeography methods, we investigate patterns of early tetrapod diversity and biogeography from the Carboniferous to early Permian to answer the following questions. (i) What are the major patterns of tetrapod diversity during this interval? (ii) How do sampling biases impact estimates of diversity, and how can we best account for them? (iii) Did the ‘CRC’ drive the development of endemism among tetrapod communities?
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