Lepidosaurian diversity in the Mesozoic-Palaeogene: the potential roles of sampling biases and environmental drivers.

Terri J Cleary,Susan E Evans,Paul M Barrett,Roger B J Benson

doi:10.1098/rsos.171830

Abstract

Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Here we estimate patterns of terrestrial lepidosaur genus diversity for the Triassic–Palaeogene (252–23 Ma), and compare observed and sampling-corrected richness curves generated using Shareholder Quorum Subsampling and classical rarefaction. Generalized least-squares regression (GLS) is used to investigate the relationships between richness, sampling and environmental proxies. We found low levels of richness from the Triassic until the Late Cretaceous (except in the Kimmeridgian–Tithonian of Europe). High richness is recovered for the Late Cretaceous of North America, which declined across the K–Pg boundary but remained relatively high throughout the Palaeogene. Richness decreased following the Eocene–Oligocene Grande Coupure in North America and Europe, but remained high in North America and very high in Europe compared to the Late Cretaceous; elsewhere data are lacking. GLS analyses indicate that sampling biases (particularly, the number of fossil collections per interval) are the best explanation for long-term face-value genus richness trends. The lepidosaur fossil record presents many problems when attempting to reconstruct past diversity, with geographical sampling biases being of particular concern, especially in the Southern Hemisphere.

Highlights

Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time
The data suggest that the trend is more like that seen in the face-value data, with sequential peaks and troughs culminating in a lower diversity estimate in the Oligocene than in the preceding time bin (Pg4–Pg5), which is still relatively high compared with the overall curve
As many previous studies have tended to focus on worldwide trends, we provide the global curve for comparison, in order to demonstrate how it is influenced by smaller-scale fluctuations in richness and to provide a pictorial summary of the current state of the lepidosaur fossil record

Summary

Introduction

Lepidosauria is a speciose clade with a long evolutionary history, but there have been few attempts to explore its taxon richness through time. Amphisbaenians, which are entirely fossorial, first appear in the early Paleocene of Belgium [30] and the USA [31], and the late Paleocene of Africa [32], though there are disputed Late Cretaceous findings [33] Their fossil record is extremely sparse, and little is known about how they diversified, with modern species-richness concentrated in Africa and South America [34,35]. They subsequently continued to decline in the Northern Hemisphere, culminating in their last appearances in North America and Europe during the Early Cretaceous [36,39,40] They are present in some Gondwanan localities in the Late Cretaceous, the Cenozoic fossil record of rhynchocephalians is sparse and, except for one occurrence in the Paleocene of Argentina [41], is confined to the area in which they are found currently, New Zealand [42]. By contrast, expanded their ranges from their first appearances in the Jurassic of Europe and Asia to become near-cosmopolitan in the modern day, except in the coldest regions of the world, and are key organisms within the terrestrial ecosystems they inhabit [43]

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Discussion

Conclusion