Macroevolutionary trends in Ceratosauria body size: insights of phylogenetic comparative methods.

Abstract

Patterns of body size evolution in dinosaurs are relevant for understanding the evolutionary trends that have shaped the disparity of phenotypes observed in the fossil record. In this sense, previous studies have suggested that Abelisauridae followed Cope´s rule and Noasauridae exhibited a phylogenetic trend towards decreasing body size. However, the absence of a comprehensive analysis including ecological, phylogenetic and socio-sexual factors make it necessary to reevaluate body size evolution in Ceretatosauria under a modern phylogenetic comparative approach. Therefore, we aimed to test whether body size evolved in Ceratosauria in accordance with Cope´s rule, evaluate what factors best explain differences in body size within Ceratosauria and examine what patterns of evolution rates, selection strength and constrain explain the diversification body size in Ceratosauria. Differences in body size were found between specialized taxa (= Late Cretaceous abelisaurids) and "generalized taxa" (= Outgroups + Noasauridae). This results suggested that the presence of a specialized feeding strategy in Late Cretaceous abelisaurids was associated with differences in body size, regardless of the phylogenetic topology and evolutionary model used. Additionally, the low levels of morphological disparity, low evolutionary rates for taxa with a specialist feeding behavior in Brownian motion model and the fossil record suggest that the evolution of body size in Late Cretaceous abelisaurids was constrained. The cursorial abilities suggested for abelisaurids joined with the specialized predation strategy could have constrained the increase in body size in Late Cretaceous abelisaurids after the extinction of carcharodontosaurids. On the other hand, Noasauridae exhibited a phylogenetic trend towards decreased body size, likely to avoid niche overlap with medium size theropods and minimize structural and maintenance cost while living in stressful environments and having a generalist diet. Understanding how the dynamics of dinosaur communities, such as competition and predator-prey interactions, operated in South America during the Late Cretaceous is crucial for reconstructing the evolutionary and ecological processes that shaped its unique faunal assemblage. Futures works should be focus on process-based community-evolution model and species distribution modeling to further understand the macroevolution dynamics of South America dinosaur community.