Diversification events and the effects of mass extinctions on Crocodyliformes evolutionary history.

Mario Bronzati,Felipe C Montefeltro,Max C Langer

doi:10.1098/rsos.140385

Abstract

The rich fossil record of Crocodyliformes shows a much greater diversity in the past than today in terms of morphological disparity and occupation of niches. We conducted topology-based analyses seeking diversification shifts along the evolutionary history of the group. Our results support previous studies, indicating an initial radiation of the group following the Triassic/Jurassic mass extinction, here assumed to be related to the diversification of terrestrial protosuchians, marine thalattosuchians and semi-aquatic lineages within Neosuchia. During the Cretaceous, notosuchians embodied a second diversification event in terrestrial habitats and eusuchian lineages started diversifying before the end of the Mesozoic. Our results also support previous arguments for a minor impact of the Cretaceous/Palaeogene mass extinction on the evolutionary history of the group. This argument is not only based on the information from the fossil record, which shows basal groups surviving the mass extinction and the decline of other Mesozoic lineages before the event, but also by the diversification event encompassing only the alligatoroids in the earliest period after the extinction. Our results also indicate that, instead of a continuous process through time, Crocodyliformes diversification was patchy, with events restricted to specific subgroups in particular environments and time intervals.

Highlights

Archosauria is one of the most successful radiations of vertebrates, with 250 Myr of evolutionary history since its origin during the Triassic [1]
This study combined the statistical support of topology-based analyses to identify diversification shifts with direct information from the fossil record to bring new data to the study of the crocodyliform evolutionary history
These evidences from two distinct methodological studies indicate that the Early Jurassic was an important moment in the establishment of the crocodyliform lineage, such radiation is hidden by the scarcity of fossils from this epoch

Summary

Introduction

Archosauria is one of the most successful radiations of vertebrates, with 250 Myr of evolutionary history since its origin during the Triassic [1]. The group is composed of two lineages, the avemetatarsalians, including birds and their non-avian dinosaur forerunners, and the pseudosuchians, including the living crocodiles [1]. 200 Ma) did not significantly reduce Avemetatarsalia diversity, but it was devastating for pseudosuchians, with Crocodylomorpha as the only group crossing the Triassic boundary [2]. Crocodylomorpha includes the ‘sphenosuchians’, a series of small, terrestrial predators restricted to Late Triassic to Late Jurassic rocks [3], and the Crocodyliformes, encompassing most of the past diversity of the group, as well as the living representatives [4]. The group survived the first event of mass extinction that followed its origin (the Triassic–Jurassic event) and surpassed the Cretaceous–Palaeogene (K/Pg) boundary With representatives found worldwide, shows an incredible variety of forms and niche occupation

Methods

Results

Discussion

Conclusion