Unappreciated diversification of stem archosaurs during the Middle Triassic predated the dominance of dinosaurs

Abstract

BackgroundArchosauromorpha originated in the middle–late Permian, radiated during the Triassic, and gave rise to the crown group Archosauria, a highly successful clade of reptiles in terrestrial ecosystems over the last 250 million years. However, scientific attention has mainly focused on the diversification of archosaurs, while their stem lineage (i.e. non-archosaurian archosauromorphs) has often been overlooked in discussions of the evolutionary success of Archosauria. Here, we analyse the cranial disparity of late Permian to Early Jurassic archosauromorphs and make comparisons between non-archosaurian archosauromorphs and archosaurs (including Pseudosuchia and Ornithodira) on the basis of two-dimensional geometric morphometrics.ResultsOur analysis recovers previously unappreciated high morphological disparity for non-archosaurian archosauromorphs, especially during the Middle Triassic, which abruptly declined during the early Late Triassic (Carnian). By contrast, cranial disparity of archosaurs increased from the Middle Triassic into the Late Triassic, declined during the end-Triassic extinction, but re-expanded towards the end of the Early Jurassic.ConclusionsOur study indicates that non-archosaurian archosauromorphs were highly diverse components of terrestrial ecosystems prior to the major radiation of archosaurs, including dinosaurs, while disparity patterns of the Ladinian and Carnian indicate a gradual faunal replacement of stem archosaurs by the crown group, including a short interval of partial overlap in morphospace during the Ladinian.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0761-6) contains supplementary material, which is available to authorized users.

The critical role of fossils in inferring deep‐node phylogenetic relationships and macroevolutionary patterns in Cornales

“…Within a paleontological context, changes in morphospace occupation and disparity can be related to ecological responses to significant environmental changes (e.g. mass extinction events; Foote, ; Erwin, ; Decombeix et al., ; Leslie, ; Xue et al., ; Foth et al., ). The morphological restriction of Late Cretaceous cornaleans may reflect the overall restricted ecological roles of angiosperms throughout the Late Cretaceous, at least in North America (Wing et al., ; Wing and Boucher, ).…”

Cranial shape variation in jacarean caimanines (Crocodylia, Alligatoroidea) and its implications in the taxonomic status of extinct species: The case of Melanosuchus fisheri

“…For instance, Piras et al (2010) and Watanabe and Slice (2014) studied the ontogenetic variation in the crocodylian skull, while Monteiro, Cavalcanti, and Sommer (1997), Fernandez Blanco, Cassini, and Bona (2014), Foth, Bona, and Desojo (2015) and Okamoto, Langerhans, Rashid, and Amarasekare (2015) focussed similar studies particularly on caimanines. In addition, Hastings and Hellmund (2017) studied the cranial shape diversity of fossil crocodylians from the Geiseltal Lagerstätte in Germany, while Young, Brusatte, Ruta, and Andrade (2010), Stubbs, Pierce, Rayfield, and Anderson (2013), Foth, Ezcurra, Sookias, Brusatte, and Butler (2016), and Wilberg (2017) performed geometric morphometric and disparity analyses on the cranial shape of crocodylian ancestors during the Mesozoic. For the geometric morphometric analyses, we examined the skull of the holotype of Melanosuchus fisheri (MCNC 243) and the four living species of jacarean Caimaninae: Melanosuchus niger, Caiman yacare, Caiman crocodilus, and Caiman latirostris (following the taxonomy of Brochu, 1999).…”

New trilophosaurid species demonstrates a decline in allokotosaur diversity across the Adamanian-Revueltian boundary in the Late Triassic of western North America

“…Archosauromorph reptiles diversified rapidly as part of the biotic recovery after the end-Permian extinction, achieving a range of shapes, sizes, and ecological roles (Dilkes 1998;Brusatte et al 2010;turner & nesBitt 2013;ezcurra 2016;Foth et al 2016). Diversification of this group included the evolution of a variety of dental morphologies that indicate a shift from carnivory to more specialized diets, including herbivory (Flynn et al 2010).…”