Sauropodomorph evolution across the Triassic–Jurassic boundary: body size, locomotion, and their influence on morphological disparity

Abstract

Sauropodomorph dinosaurs were the dominant medium to large-sized herbivores of most Mesozoic continental ecosystems, being characterized by their long necks and reaching a size unparalleled by other terrestrial animals (> 60 tonnes). Our study of morphological disparity across the entire skeleton shows that during the Late Triassic the oldest known sauropodomorphs occupied a small region of morphospace, subsequently diversifying both taxonomically and ecologically, and shifting to a different and broader region of the morphospace. After the Triassic–Jurassic boundary event, there are no substancial changes in sauropodomorph morphospace occupation. Almost all Jurassic sauropodomorph clades stem from ghost lineages that cross the Triassic–Jurassic boundary, indicating that variations after the extinction were more related to changes of pre-existing lineages (massospondylids, non-gravisaurian sauropodiforms) rather than the emergence of distinct clades or body plans. Modifications in the locomotion (bipedal to quadrupedal) and the successive increase in body mass seem to be the main attributes driving sauropodomorph morphospace distribution during the Late Triassic and earliest Jurassic. The extinction of all non-sauropod sauropodomorphs by the Toarcian and the subsequent diversification of gravisaurian sauropods represent a second expansion of the sauropodomorph morphospace, representing the onset of the flourishing of these megaherbivores that subsequently dominated in Middle and Late Jurassic terrestrial assemblages.

A path to gigantism: Three‐dimensional study of the sauropodomorph limb long bone shape variation in the context of the emergence of the sauropod bauplan

“…Our qualitative analyses of Tazoudasaurus limb bones corroborates this affirmation because this taxon is found in the Pliensbachian‐Toarcian of Morocco (Allain & Aquesbi, 2008 ). These changes likely contributed to the success of the sauropod bauplan, following the faunal turnover that occurred during the Pliensbachien‐Toarcian leading to the dominance of these taxa in post‐Toarcian ecosystems (Allain & Aquesbi, 2008 ; Apaldetti et al, 2021 ; Pol et al, 2020 ).…”

Climatic controls on the ecological ascendancy of dinosaurs

“…1,5 In particular, sauropodomorph dinosaurs increased in geographic range and abundance across the Triassic to Jurassic transition, although without associated increases in morphological disparity. 32 Our results show that the Early Jurassic is marked by a broadening of the MAT conditions under which sauropodomorphs occurred. The majority of these occurrences are at cooler temperatures than known from the Late Triassic (Figures 2A and 2C), yet sauropodomorphs in both the Late Triassic and Early Jurassic show similar bounds on their overall MAT distribution (Figures 2A and 2C).…”

“…Phylogenetic mapping in our study indicates that the shift towards warmer climatic niches occurred around the base of Sauropoda, documenting an important shift in climatic niche synchronous with major phenotypic changes involved in sauropod origins. 32,36 The extent to which this change in climatic niche is related to features such as giant adult body size and highly accelerated growth rates 37 is not currently known but may be important in understanding sauropod biology. For example, bone histology indicates that sauropods underwent sustained year-round growth, contrasting with cyclical, seasonally interrupted growth in other sauropodomorphs, [36][37][38] and some authors have suggested that this may have resulted from the presence of mammal-like endothermic homeothermy in the group.…”

Osteology of the sauropodomorph dinosaur Jaklapallisaurus asymmetricus from the Late Triassic of central India

“…A later analysis using a modified version of that data matrix recovered this same taxonomic content and unresolved relationships between Jaklapallisaurus asymmetricus and the other plateosaurids (e.g., Pretto et al, 2018). More recently, the analysis of a new iteration of this dataset recovered Jaklapallisaurus asymmetricus as the sister taxon to the clade composed of Plateosauridae and a group formed by Unaysaurus tolentinoi + ( Pradhania gracilis + Macrocollum itaquii ) (Apaldetti et al, 2021). A subsequent analysis of another new version of this data matrix found the most disruptive result recovered so far regarding the position of Jaklapallisaurus asymmetricus (Pol et al, 2021).…”