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

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–Lagerstätte (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.

Drivers of the artiodactyl turnover in insular western Europe at the Eocene–Oligocene Transition

“…These pre-and post-EOT species longevity estimates are relatively low in comparison with other analyses on artiodactyls [i.e., 5.6 Myr in (80); 4.4 Myr in (81)]. The limited geographic range (~1800 km²) of the study area and the short time range considered (below 10 Myr for each fauna) can explain these results (10,45,82). Furthermore, the observed differences in species longevity and extinction probability between Eocene and Oligocene faunas mirror different climatic regimes characterizing both periods.…”

“…We compiled all fossil occurrences (2,196) of European artiodactyls at the specific (90) and generic (39) levels from 55 Quercy localities (Dataset S1), spanning the middle Eocene-late Oligocene interval (42 to 25 Mya). This work follows the compilation performed by (45) for the Cainotherioidea. Species occurrences for each locality result from the direct systematic revision and determination of the fossil material (dental, mandibular and cranial).…”

“…Land bridges due to local tectonics in the Alpine and Balkan regions (27) and eustatic sea level falls (28) allowed for dispersal of new faunas toward western Europe during the early Oligocene (36,43). The prevailing hypothesis is that endemic artiodactyls were supplanted, i.e, via competitive exclusion, by immigrant ruminants that possessed a more advanced dental morphology (selenodonty) and type of digestive physiology (rumination), advantageous in a general context of habitat opening (44,45,48).…”

“…Artiodactyls were a major component of the endemic European mammal fauna during the Eocene ( 33 , 44 , 45 ). Previous studies indicated that they experienced a diversity drop during the EOT with preliminary evidence suggesting they were mostly replaced by crown artiodactyl taxa (ruminants, pigs, hippos) during the Oligocene ( 33 , 36 , 44 ).…”

Anatomy and phylogeny of an exceptionally large sebecid (Crocodylomorpha) from the middle Eocene of southern France

“…Reports of sebecid occurrences based on isolated ziphodont teeth can easily be confounded with that of planocraniids, which have been identified since Cuvier (1824), so sebecids have not yet been positively identified in the Paris Basin either. Intra-European endemism during the Eocene has been proposed on the basis of the distribution of Eocene mammals such as hoofed mammals, emphasizing distinct biogeographic entities between Iberia and southern France, and the rest of Europe (e.g., Badiola & Cuesta, 2008; Danilo et al, 2013; Weppe et al, 2021). Whether coexisting taxa such as sebecids were also part of this pattern of provincialism should be looked at more closely.…”