Evolutionary trends of caviomorph rodents as elucidated using their oldest foot anatomy

Abstract

Extant caviomorph rodents exhibit a wide arrayof locomotor types and substrate preferences, which arereflected in their foot morphology. It is not known when thesepatterns were established or how they evolved in this taxonomicallyand ecologically diverse clade. We studied the anatomyof the earliest preserved feet of caviomorphs representedby the late Oligocene stem octodontoid Platypittamys and theEarly Miocene cavioid Neoreomys, stem octodontoid Sciamysand erethizontoid Steiromys. Integrating information providedby extant species, we performed qualitative and geometricmorphometric analyses, reconstructing ancestral morphologiesto interpret the evolution of the foot of caviomorphsthrough a time-scaled phylogeny, and infer locomotor behaviours.We identified an important morphological disparity inthese early genera that is explained by the presence of differentlocomotor adaptations and phylogenetic signal at differenttaxonomic levels. Neoreomys was probably generalized ambulatory,Steiromys possibly scansorial, Platypittamys possiblyambulatory with digging abilities, and Sciamys was probablyagile ambulatory–scansorial. Our study indicated that severalfoot features can distinguish higher taxonomic groups ofcaviomorphs, at least since the Early Miocene. Early in theirhistory, morphological constraints would have limited thecapacity of evolutionary change more markedly in Cavioideaand Chinchillidae. In Cavioidea, at least two evolutionarytrends were detected. Among octodontoids, extant octodontidsand Platypittamys showed convergent anatomical patterns.Erethizontoidea retained a foot essentially unchangedsince the Early Miocene after acquiring a noteworthy evolutionaryinnovation. In sum, the earliest foot morphologies ofcaviomorphs are very important in identifying evolutionarytendencies and the origin of their postcranial disparity.