Environmental drivers of crocodyliform extinction across the Jurassic/Cretaceous transition

Abstract

Crocodyliforms have a much richer evolutionary history than represented by their extant descendants, including several independent marine and terrestrial radiations during the Mesozoic. However, heterogeneous sampling of their fossil record has obscured their macroevolutionary dynamics, and obfuscated attempts to reconcile external drivers of these patterns. Here, we present a comprehensive analysis of crocodyliform biodiversity through the Jurassic/Cretaceous (J/K) transition using subsampling and phylogenetic approaches and apply maximum-likelihood methods to fit models of extrinsic variables to assess what mediated these patterns. A combination of fluctuations in sea-level and episodic perturbations to the carbon and sulfur cycles was primarily responsible for both a marine and non-marine crocodyliform biodiversity decline through the J/K boundary, primarily documented in Europe. This was tracked by high extinction rates at the boundary and suppressed origination rates throughout the Early Cretaceous. The diversification of Eusuchia and Notosuchia likely emanated from the easing of ecological pressure resulting from the biodiversity decline, which also culminated in the extinction of the marine thalattosuchians in the late Early Cretaceous. Through application of rigorous techniques for estimating biodiversity, our results demonstrate that it is possible to tease apart the complex array of controls on diversification patterns in major archosaur clades.

Increased pliosaurid dental disparity across the Jurassic–Cretaceous transition

“…; Tennant et al . , ), and the same was hypothesized for plesiosaurs (Benson & Druckenmiller ). However, the hypothesized turnover among plesiosaurs could in part be explained by poor sampling: few plesiosaur specimens are known from this time interval.…”

An unusual small-bodied crocodyliform from the Middle Jurassic of Scotland, UK, and potential evidence for an early diversification of advanced neosuchians

“…Pachycheilosuchus was originally described as a possible atoposaurid (Rogers 2003), but Turner (2015) recovered it at the base of Eusuchia. Other studies have recovered this species in radically different positions, such as: in a more basal position within Neosuchia, closer to the split with Tethysuchia (Adams 2014); as a derived neosuchian but basal to Eusuchia (Narváez et al 2015); as a basal neosuchian, even more basal than the Tethysuchia-Eusuchia split (Tennant et al 2016b); or in a clade with an assortment of hylaeochampsids and susisuchids (Schwarz et al 2017). The phylogeny of Turner (2015) is consistent with Buscalioni et al (2011) in the monophyly of Hylaeochampsidae, despite the fact that the latter study found Pietraroiasuchus as the sister group of Pachycheilosuchus (although they did not sample Acynodon).…”

“…However, the various phylogenetic analyses appear to converge on a divergence between the large-bodied and primarily aquatic neosuchian clades (Pholidosauridae þ Dyrosauridae) and the relatively smaller-bodied, terrestrial or semi-aquatic clades (although the position of Goniopholididae is variable; Adams 2014; Turner 2015; Young et al 2016b;Schwarz et al 2017). Yet little is known about neosuchians before the Late Jurassic due to a patchy non-marine fossil record (Mannion et al 2015;Tennant et al 2016b). The earliest definitive record of pholidosaurid material comes from the Late Jurassic of Uruguay and France (Fortier et al 2011).…”

“…Apparently, terrestrial and freshwater species were stuck in a low point of their diversity, although this could be an artefact of the notoriously poor Middle Jurassic tetrapod fossil record . Sparse sampling during this interval complicates our understanding of the diversification patterns of non-pelagic crocodyliforms (Bronzati et al 2015;Mannion et al 2015;Tennant et al 2016b), meaning that new Middle Jurassic fossils are critical.…”

“…By the Early Cretaceous, European faunas were composed of a more diverse assemblage of neosuchians, including goniopholidids, pholidosaurids, bernissartiids, putative atoposaurids and hylaeochampsids (e.g., Salisbury & Naish 2011;Sweetman et al 2015). Ghost lineage analyses imply that, depending on the systematic position of the Cretaceous clades, some major neosuchian lineages may have originated during the dark period of the Middle Jurassic (e.g., Bernissartiidae, Hylaeochampsidae, Paralligatoridae and Pholidosauridae: Bronzati et al 2015;Turner 2015;Tennant et al 2016b).…”