Evolutionary drivers, morphological evolution and diversity dynamics of a surviving mammal clade: cainotherioids at the Eocene--Oligocene transition

TL;DR

This study examines how environmental changes during the Eocene--Oligocene transition influenced the diversification and morphological evolution of Cainotherioidea, a mammal clade that survived and radiated after the period of global upheaval.

Contribution

It provides a detailed analysis of the diversification dynamics and morphological adaptability of Cainotherioidea during a critical global environmental transition.

Findings

Cainotherioids experienced a major speciation burst in the early Oligocene.

Extinction events aligned with environmental changes at the EOT and late Oligocene.

Morphological adaptability contributed to their survival and evolutionary success.

Abstract

The Eocene--Oligocene transition (EOT) represents a period of global environmental changes particularly marked in Europe and coincides with a dramatic biotic turnover. Here, using an exceptional fossil preservation, we document and analyse the diversity dynamics of a mammal clade, Cainotherioidea (Artiodactyla), that survived the EOT and radiated rapidly immediately after. We infer their diversification history from Quercy Konzentrat--Lagerst{\"a}tte (south-west France) at the species level using Bayesian birth--death models. We show that cainotherioid diversity fluctuated through time, with extinction events at the EOT and in the late Oligocene, and a major speciation burst in the early Oligocene. The latter is in line with our finding that cainotherioids had a high morphological adaptability following environmental changes throughout the EOT, which probably played a key role in the survival and evolutionary success of this clade in the aftermath. Speciation is positively associated with temperature and continental fragmentation in a time-continuous way, while extinction seems to synchronize with environmental change in a punctuated way. Within-clade interactions negatively affected the cainotherioid diversification, while inter-clade competition might explain their final decline during the late Oligocene. Our results provide a detailed dynamic picture of the evolutionary history of a mammal clade in a context of global change.