Synopsis of the stratigraphical distribution of the Villafranchian equids, tapirids and rhinocerontids of western Europe

Abstract

Four equids characterize the Villafranchian fossil communities of Western Europe, Equus livenzovensis, E. stenonis, E. stehlini and E. gr. bressanus-sussenbornensis. The large-sized E. livenzovensis, a probable offspring of the North American E. simplicidens, dispersed in Eurasia approximately during the interval spanning about 2.5/2.4 Ma (Montopoli Faunal Unit). E. stenonis is first represented in the St. Vallier F.U. assemblages. This species formed a variety of subspecies spread throughout Western Europe and distinguished only on dimensional basis. E stenonis gave rise to a middle-small-sized asinine species, E. stehlini, which appeared in Tuscany at the time of the Tasso F.U. and seems to be also represented in the fossil assemblage of Vailonnet, transitional to the Galerian faunas. Another possible offspring of E. stenonis, E. gr. bressanus-sussenbornensis, one of the largest equids of Eurasia, characterizes the latest Villafranchian and earliest Galerian communities. The Villafranchian tapirs of Western Europe are represented only by one species, Tapirus arvernensis. Two subspecies are known, the small-sized T. arvemensis minor and the larger-sized T. arvernensis arvernensis. The phylogenetic relationships of T. arvernensis are still debated. Remains of this species characterize the Late Turolian to Lower Villafranchian communities. Four rhinocerontids, namely Stephanorhinus jeanvireti, S. etruscus, S. hundsheimensis and S. hemitoechus, distributed in Western Europe during the Villafranchian. The phylogenetic relationships between these species are presently unresolved. Stephanorhinus jeanviretiis a large-sized, cursorial, Early Villafranchian species that apparently shares a number of common cranial characters with S. hundsheimensis. At the moment, the first ascertained occurrences of S. etruscus are from the Lower Villafranchian localities of Citta della Pieve (Perugia) and Montopoli (Pisa); it therefore co-occurred for a while with S. jeanvireti. S. etruscus apparently disappeared at the time of the Villafranchian-Galerian faunal turnover (1.0-0.7 Ma). Peculiar small-sized specimens with S. etruscus-S. hundsheimensis affinities are known, in the Netherlands, in Germany and in Italy, from levels dated to the end of the Early Pleistocene. These specimens seem to be good markers, given their sharp stratigraphic distribution. The most ancient S. hundsheimensis representatives characterize very late Villafranchian communities. The species shares a number of dental and postcranial features with S. etruscus, which attests to a possible descent from the latter species. Ancient occurrences of S. hemitoechus are stratigraphically problematic. A partial mandible is known from Croce-dei-Cappuccini (Upper Valdarno) and a partial skull, with S. hemitoechus affinities, was found at Grezzano (Mugeilo). It is therefore possible that the species actually made its first appearance in times slightly older than commonly accepted.