Decline of artiodactyls endemic to Europe – DEADENDER

DEADENDER is composed of two complementary work packages. The first one aims at getting an accurate picture of the EEA in terms of specific diversity, temporal distribution, and ecology – before, at, and after the GC. This will set 1) an up-to-date systematic framework for fossil artiodactyls from Quercy, 2) a refined temporal setting for Quercy fossiliferous localities, and 3) an accurate, multi-proxy determination of the paleoecology of extinct Quercy artiodactyls, using the internal structures of the cranium related to senses organs, and microtexture analyses of the teeth enamel. The second work package will explore the tempo of speciation and extinction of EEA clades and the contribution of abiotic (past environmental changes) and biotic factors (clade competition, species traits) over their diversity dynamics (diversity analyses). It will also provide precious information on the evolutionary mechanisms that underlie phenotypic evolution of EEA clades, which may determine their response to environmental and biotic stresses.

An initial field campaign made it possible to complete the paleontological record, to specify the age of certain deposits, and to give a more complete picture of the taxonomic assemblage for different periods of interest. We chose to study first the dynamics of the diversity of one family in particular: the Cainotheriidae. The focus on a small, diverse and well-documented taxonomic group allowed us to refine our approach and our protocol of analysis sequences before implementing the study of diversity dynamics at the scale of the order. We highlighted a local taxonomic diversification of Cainotheriidae after the Grande Coupure, and clarified the phylogenetic relationships within the family and its controversial position within Artiodactyla. We also documented the early evolutionary history of the family by identifying a new genus and a new species that represents the first branch of their history. This makes it possible to follow the development of their peculiar dental morphology. Diversity analyses of Cainotheriidae indicate a weak role of temperature and a dominant role of competition in the evolution of their diversity dynamics. In order to specify the stratigraphic and temporal context and the sedimentary dynamics of the sites of interest in relation to the paleoenvironment, numerous geochemical and mineralogical analyses have been carried out. The results indicate that climate changes during the Grande Coupure are only expressed through the fossilized sedimentary structures in the fillings (channels and desiccation slits), and lead us to consider an important role of bacterial mechanisms in the mobilization and precipitation of phosphate.

The first period has been devoted, for the paleontological aspect, to testing and refining the analysis protocol on a group of EEA in particular, the Cainotheriidae. We will now apply these analyses on a larger scale, encompassing the group of interest as a whole. The microtexture analyses of dental enamel, currently in progress, will provide valuable information on the diet of the EEAs. At the same time, the study of endocranial structures, also already initiated, will provide other indicators of their paleobiology such as their hearing ability or brain complexity. Diversity analyses will be conducted at the Artiodactyla scale, based on a completed paleontological register and a revised taxonomy. A complementary aspect will be to explore the potential effect of certain adaptations of EEAs on the evolution of their phenotype. This will make it possible to test the effect of discrete traits such as diet on continuous traits such as parameters related to sensory specialization (e.g. relative size of olfactory bulbs or cochlea volume) or cognitive abilities (e.g. neocortical complexity).

Three articles are published:

Weppe R. et al. 2020 Cainotheriidae (Mammalia, Artiodactyla) from Dams (Quercy, SW France); phylogenetic relationships and evolution around the Eocene-Oligocene transition (MP19-MP21). Journal of Systematic Palaeontology 18(7), 541-572. DOI: 10.1080/14772019.2019.1645754

Assemat A. et al. 2020. The ossicular chain of Cainotheriidae (Mammalia, Artiodactyla). Journal of Anatomy 1-13. (first online) DOI: 10.1111/joa.13190

Assemat A. et al. 2020. 3D models related to the publication: The ossicular chain of Cainotheriidae (Mammalia, Artiodactyla). MorphoMuseuM (first online) DOI:10.18563/journal.m3.110

Results of the field campain and paleontological studies have been presented through 4 communications at two international congresses:
- Congrès de l’Association Paléontologique Française, Aix-en-Provence, 2019

Weppe R. et al. Les Cainotheriidae (Mammalia, Artiodactyla) de Dams (Quercy, SW France); relations phylogénétiques et évolution de leur diversité à la transition Eocène-Oligocène (MP19-MP21).

Orliac M. et al. La phosphatière de Dams (Quercy), un nouveau site fossilifère majeur encadrant la Grande Coupure de Stehlin (transition Eocène-Oligocène).

Assemat A. et al. 2019. La chaîne des osselets de l’oreille moyenne des Cainotheriidae (Mammalia, Artiodactyla)

- Congrès PalEurAfrica, Bruxelles, Belgique 2019

Weppe R. et al. Cainotheriidae (Mammalia, Artiodactyla) from Dams (Quercy, SW France); phylogenetic relationships and evolution around the Eocene-Oligocene transition (MP19-MP21).

Understanding biological extinction is a central topic in evolutionary biology and paleontology. After the mass extinction of non-avian dinosaurs, the Eocene-Oligocene transition (ca. 33.9–33.5 Ma) is considered as a key step in Cenozoic climate evolution and it coincides with one of the main extinction events in Europe during the Cenozoic: the Grande Coupure (GC). Most of the species documented in Europe after the GC had no close relatives in the preceding fauna. Indeed, mammals had evolved independently in island Europe during the Eocene, after the North Atlantic split from North America ca. 53 Mya. The overarching goal of DEADENDER is to dissect the process of biological extinction using Endemic European Artiodactyls (EEA) to investigate the response of related animals to local environment changes, and the impact of biotic drivers on their specific diversity (and final decline). DEADENDER proposes an innovative approach combining the most accurate fossil record at world scale for the Eocene-Oligocene interval with cutting-edge analytic methods, both in terms of 3D morphological investigation and of diversity dynamics. This project will exploit the unparalleled fossil record from the Quercy phosphate infillings localities in France (certified UNESCO Global Geopark) to test the impact of biotic (intrinsic like diet, body mass, brain complexity, or extrinsic such as competition with other mammals or predation) and abiotic factors (temperature, sea level) on the diversity dynamics of EEA. DEADENDER contrasts with previous approaches by its integrative, multifactorial nature, combining altogether biotic and abiotic factors to get a better understanding of the response of organisms to environmental changes. This comprehensive approach will allow an accurate understanding of the drivers of diversity dynamics for a given clade.
DEADENDER is composed of two complementary work packages. The first one aims at getting an accurate picture of the EEA in terms of specific diversity, temporal distribution, and ecology – before, at, and after the GC. This will set 1) an up-to-date systematic framework for fossil artiodactyls from Quercy, 2) a refined temporal setting for Quercy fossiliferous localities, and 3) an accurate, multi-proxy determination of the paleoecology of extinct Quercy artiodactyls (3D dental microwear analyses + virtual reconstruction of brain cast and inner ear based on CT data). The second work package will explore the tempo of speciation and extinction of EEA clades and the contribution of abiotic (past environmental changes) and biotic factors (clade competition, species traits) over their diversity dynamics. It will also provide precious information on the evolutionary mechanisms that underlie phenotypic evolution of EEA clades, which may determine their response to environmental and biotic stresses.
Accordingly, DEADENDER will allow for: 1) clarifying basal relationships of EEA clades within Artiodactyla phylogeny, 2) providing accurate speciation and extinction rates through time for each EEA clade, 3) defining the effect(s) of environmental variables on speciation and extinction of each EEA clade and of EEA groups sharing similar ecological/physiological characteristics, 4) identifying the role of competition on the speciation and extinction rates of each EEA clade, and 5) exploring the mechanisms that underlie phenotypic evolution of EEA clades. Altogether, this will give access to key aspects of the EEA extinction including the understanding of specificities of extinction victims, survivors, and replacement taxa, and potential links between life history traits and extinction magnitude/survivorship per clade.
The deliverables of DEADENDER will directly document the diversity and evolutionary potential of species to adapt to past environmental changes. In the general context of worldwide erosion of biodiversity, beyond scientific community, DEADENDER has several potential outreaches for a general audience.