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. 2015 Sep 24:6:8438.
doi: 10.1038/ncomms9438.

Climate constrains the evolutionary history and biodiversity of crocodylians

Philip D Mannion  1 , Roger B J Benson  2 , Matthew T Carrano  3 , Jonathan P Tennant  1 , Jack Judd  1 , Richard J Butler  4
Affiliations

Climate constrains the evolutionary history and biodiversity of crocodylians

Philip D Mannion et al. Nat Commun. .

Abstract

The fossil record of crocodylians and their relatives (pseudosuchians) reveals a rich evolutionary history, prompting questions about causes of long-term decline to their present-day low biodiversity. We analyse climatic drivers of subsampled pseudosuchian biodiversity over their 250 million year history, using a comprehensive new data set. Biodiversity and environmental changes correlate strongly, with long-term decline of terrestrial taxa driven by decreasing temperatures in northern temperate regions, and biodiversity decreases at lower latitudes matching patterns of increasing aridification. However, there is no relationship between temperature and biodiversity for marine pseudosuchians, with sea-level change and post-extinction opportunism demonstrated to be more important drivers. A 'modern-type' latitudinal biodiversity gradient might have existed throughout pseudosuchian history, and range expansion towards the poles occurred during warm intervals. Although their fossil record suggests that current global warming might promote long-term increases in crocodylian biodiversity and geographic range, the 'balancing forces' of anthropogenic environmental degradation complicate future predictions.

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Figures

Figure 1
Figure 1. Global raw counts of pseudosuchian genera through the last 250 million years.
Red line represents non-marine taxa and the blue line represents marine taxa. Silhouettes of representative pseudosuchians are modified from work by Dmitry Bogdan, Evan Boucher, Scott Hartman, Mike Keesey, Nobumichi Tamura (hosted at: http://phylopic.org, where all license information is available).
Figure 2
Figure 2. Subsampled pseudosuchian genus biodiversity.
(a) Non-marine biodiversity within continental regions for a subsampling quorum level of 0.4, and palaeotemperature (δ18O) curve for the last ∼70 Myr ago (with weighted means (yellow circles)). (b) Global marine biodiversity for a subsampling quorum level of 0.4 (blue circles) and sea level curve (with weighted means (yellow circles)). Adamantina, Adamantina Formation subsampled crocodylomorph biodiversity; EECO, Early Eocene Climatic Optimum; MECO, Mid-Eocene Climatic Optimum; MMCO, Mid-Miocene Climatic Optimum; PETM, Paleocene-Eocene Thermal Maximum. Linear regression for pooled regional subsampling results on geological age in millions of years: log10 subsampled genera=0.0015 × age+0.244 (P=0.002; N=38; R2=0.221).
Figure 3
Figure 3. Regional plots of subsampled biodiversity versus palaeolatitudinal centroid and subsampling curves for non-marine genera.
(a) Triassic–early Late Cretaceous (K6) subsampled biodiversity versus palaeolatitudinal centroid. (b) Late Triassic (Tr4) log10-transformed subsampling curves. (c) Late Cretaceous (K7 and K8) subsampled biodiversity versus palaeolatitudinal centroid. (d) Paleogene subsampled biodiversity versus palaeolatitudinal centroid. (e) Neogene subsampled biodiversity versus palaeolatitudinal centroid. (f) Early Neogene (Ng1) log10-transformed subsampling curves. (g) Middle Neogene (Ng2) log10-transformed subsampling curves. Dashed arrows denote notable changes in biodiversity between consecutive time intervals within a single continental region. K, Cretaceous; Ng, Neogene; Tr, Triassic.
Figure 4
Figure 4. Palaeolatitudinal distribution of Pseudosuchia.
(a) Palaeolatitudinal spread of all non-marine pseudosuchian (red circles) and all non-marine tetrapod (black circles) occurrences through time. (b–d) Global palaeocontinental reconstructions from Fossilworks showing the distribution of all pseudosuchian occurrences in the (b) Cretaceous (145–66 Myr ago), (c) Eocene (56–33.9 Myr ago) and (d) Miocene (23–5.3 Myr ago).
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