Significance of the Past LArge Semiaquatic Herbivores: evolutionary history of a polyvalent ecological niche within Cetartiodactyla

Informations

Funding country

France

Acronym

SPLASH

URL

-

Start date

1/1/2015

End date

-

Budget

260,906 EUR

Fundings

Abstract

Large semiaquatic herbivores (LSH, e.g. living hippopotamids) were once widespread ecosystem engineers of terrestrial and wet habitats, and had a pervasive role in the Cenozoic evolutionary sequence linking Cetacea to artiodactyls. SPLASH will use a clade of LSH cetartiodactyls, the Hippopotamoidea, for investigating how the interplay between evolutionary mechanisms, ecological specialization, and environmental constraints shape the diversity and distribution of mammals. The evolutionary history of Hippopotamoidea (Hippopotamidae + anthracotheres) is tightly linked to that of Cetacea (clade Cetancodonta), but unlike the latter, it was little studied until recently. Hippopotamoidea had a wide spatiotemporal distribution (from Eocene to today, from Old World to northern and central America), documented by a particularly abundant fossil record. They display a wide array of ecologies and semiaquatic adaptations have developed multiple times in different hippopotamoid lineages. SPLASH research on Hippopotamoidea will follow a two-fold approach. First, we will describe the paleobiology of key hippopotamoid species, using a broad combination of spearheading methods for morphofunctional and paleoecological reconstructions. We will describe the sensorial, locomotor, dietary, and aquatic adaptions of these species. This will allow establishing suites of features depicting the LSH adaptive zone. We expect observing different suites corresponding to different degrees of water-dependence, as well as co-occurring adaptations favored by semiaquatic habits (e.g., linked to gregarism). Second, we will integrate this paleobiological information within a comprehensive phylogenetic framework. For this, SPLASH will perform a renewed appraisal of the LSH diversity within Cetancodonta. It will also produce novel morphological character datasets based on direct observations of a wide array of cetancodonts. We expect that the phylogenetic analyses of the resulting data matrix will provide new support and information on the relationship between Hippopotamidae and “Anthracotheriidae”), and will clarify basal relationships including the placement of Cetacea relative to other cetartiodactyls. We also expect testing the molecular grouping of Cetancodonta with Ruminantia. We will map our paleobiological data on these phylogenetic results. We expect to confirm the prevalence of the LSH niche and to describe its sequence of parallel rises and declines within Hippopotamoidea and their Eocene relatives. Based on these results, we will propose revised character optimizations for major nodes of cetartiodactyls evolutionary history (notably the common ancestor to Cetacea and Hippopotamidae). By comparing our mapped data to the record of environmental evolution, we will notably examine the development of LSH adaptations in response to environmental stress as well as the LSH extinctions in response to Neogene cooling and aridification. SPLASH results should be considered as “evolutionary natural experiments” that ran over millions of years during the Cenozoic. These “experiments” will be used to generate and/or test macroevolutionary hypotheses, such as the relevance of deep homology for large mammal evolution. SPLASH will be also a source of novel data on Cenozoic ecosystems, interesting paleoenvironmental researches and notably on the environmental context of human evolution. SPLASH should finally provide researches on conservation with useful comparative data on semiaquatic organism responses within several past climatic and environmental settings not affected by recent anthropogenic action.