Listriodontinae (Suidae, Mammalia), their evolution, systematics and distribution in time and space

Representatives of the pig subfamily Listriodontinae are found in Miocene deposits of Africa and Eurasia. Listriodontinae differ from other suids in morphology and size of the incisors, which may be three times as large as in their suid relatives. Many listriodonts showed a tendency to develop lophodonty and in some species the males developed large median ‘horns’ on the frontals; smaller protuberances above the orbits are found in both males and females. On account of molar similarity, some listriodonts have previously been described erroneously as tapirs. The oldest representatives of the subfamily occur in strata of Early Miocene, the youngest in strata of early Late Miocene age, documenting a chronostratigraphical range from c. 20 to 9 Ma. Listriodonts from 350 localities in Eurasia and Africa were studied in order to clarify their systematics, study their palaeoecology, unravel phylogenetic relationships, establish a more refined biostratigraphical framework, and better understand migration and dispersal patterns. Problems related to the geographical distribution of species and phylogenetic lineages were focused on in an attempt to improve our knowledge of the evolution of the group, study the potential of lineages for long-distance correlations, and – document the relationship between migration/dispersal events, eustatic sea level changes and alaeogeographical reorganisations resulting from plate tectonics. Listriodont evolution was marked by major changes in tooth morphology. A comprehensive nomenclature based on the Cope-Osborn terminology is proposed to facilitate discussions and comparisons of dental structures in suids and other groups of Artiodactyla. Four new species are described, viz. Lopholistriodon pickfordi, Kubanochoerus marymunnguae, Kubanochoerus mancharensis and Bunolistriodon anchidens. The genera Nguruwe (1 species) and Lopholistriodon (4 species) are placed in the Lopholistriodontini (new tribe). Libycochoerus is included in Kubanochoerus (6 species), the sole genus of the Kubanochoerini. Small species often placed in Libycochoerus are reassigned to Bunolistriodon (10-12 species), which, together with Listriodon (2 species), is placed in the Listriodontini. Kenyasus is excluded from the Listriodontinae. The ecological significance of incisor morphology and morphometry, thickness of molar enamel, geographical and temporal distribution and species abundances are discussed. Changes in listriodontine distribution and abundance during the Middle and Late Miocene reflect environmental changes. The evolutive trends in listridont lineages are used to improve local biostratigraphy and long distance correlations. During the study period, northern Eurasia, a subcontinent comprising SE Europe & Turkey, the Indian Subcontinent and Africa were separate landmasses. Dispersals of listriodonts in thses landmasses coincide with those of other mammals and represent “dispersal events”. Such dispersal events occurred simultaneously in the different land masses. Some of those dispersal events are known under the name Proboscidean Datum Event and are widely believed to be allowed for by eustatic sea level low stands. The different dispersal events are related to particular eustatic sea level low stands of Haq et al. (1987). Dates as inferred from the the relation between dispersal events and the dated curves of Haq et al. agree well with the available radiometric and paleomagnetic dates of mammal localities.