Insights into the habitat of Middle Permian pareiasaurs (Parareptilia) from preliminary isotopic analyses

Abstract

Pareiasaurs were an abundant group of large herbivores during Middle and Late Permian times. The habitat of pareiasaurs has proven enigmatic, and ecological interpretations from anatomical and taphonomic data have included aquatic, semi-aquatic to fully terrestrial lifestyles. Insight into the ecology of extinct taxa can also be gained from stable isotope analyses, and interpretations benefit from studies of multiple, coeval groups. Here, we report the first stable carbon and oxygen isotope analyses from the enamel, dentine and bone of pareiasaurs and contemporaneous therapsids (dinocephalians and therocephalians), in specimens recovered from the Permian Tapinocephalus to lower Pristerognathus Assemblage Zones of South Africa. Previous ecological inferences for dinocephalians (riparian to terrestrial) and therocephalians (terrestrial) are less ambiguous than reconstructions for pareiasaurs and provide an independent reference for interpreting stable isotope measurements. Oxygen isotopes of enamel carbonate were indistinguishable between pareiasaurs and therocephalians, which had higher values than dinocephalians. The data suggest that dinocephalians and pareiasaurs (megaherbivores) inhabited different ecological niches and that pareiasaurs may have shared a terrestrial habitat with therocephalians (carnivores). Our results agree with earlier suggestions of a terrestrial lifestyle among pareiasaurs and provide evidence of niche partitioning among large coeval Capitanian herbivores of South Africa.