Introduction: Mammals Biochronology and Paleoecology of the Euro-Mediterranean Quaternary

1. Introduction

The Quaternary is a time of fundamental climatic shifts and environmental changes that highlight the need for a thorough investigation from different perspectives and at multiple scales to disentangle the factors involved in the response of the biota. In turn, recognizing bioevents (e.g., the dispersal or extinction of species) and relating them to geological time is crucial for correlating changes between distant geographic regions. The mammalian fossil record is widely used for biochronological correlations and paleoecological reconstructions of the Euro-Mediterranean region and represents an especially important proxy for inferring the timing, pattern, and paleoenvironmental context of the earliest events of hominin dispersal into Europe. Conducting research on the response of mammals to the paleoenvironmental changes in the Euro-Mediterranean Quaternary and developing a consistent and precise biochronological framework require the thoughtful integration of data and schemes from different geographic areas.

With the aim of fostering progress in this direction, we organized a scientific session on “Mammals Biochronology and Paleoecology of the Euro-Mediterranean Quaternary” during the XXI INQUA Conference, which took place in Rome in July 2023. With attendees from more than ten countries, the session was indeed a stimulating occasion for discussion. This Special Issue gathers selected papers derived from original contributions presented during the session or developed as a result of the contextual scientific exchange. A brief summary of the articles is presented below.

2. Summary

The articles of this Special Issue cover a large geographical scope, encompassing most of the northern Mediterranean region and adjacent areas, and a wide range of approaches, including biochronological to paleoecological research and more. Small and large mammals are considered, with a preponderance for the latter. Carnivora and hippopotamuses receive particular attention, with dedicated papers and specific digressions in other works. Recurrent themes include the establishment of local biochronological/biostratigraphic schemes or the identification or refinement of the knowledge on faunal dispersal events and their correlation. Paleoecological and paleoenvironmental insights, often with considerations on implications for hominins, are also present in several works. Among the articles, there are some that begin with taxonomic descriptions or specific sites, but even in these cases, the results are contextualized in a broader European dimension.

Spassov [1] presents a critical compilation of large mammalian dispersal events and a correlation of the Villafranchian (ca. 3.6/3.4–1.2 Ma) biochronology between Eastern and Western Europe. Taxa whose dispersal is discussed in detail include Mammuthus, Equus, Canis, Acinonyx, Puma, Panthera, Pachycrocuta, Hippopotamus, and Bison. Significant faunal turnovers occurred: during the final Pliocene (early Villafranchian); at the beginning of the Pleistocene (middle Villafranchian); around 2.2–2.1 Ma, as represented by the fauna of sites such as Slivnitsa, Coste San Giacomo, and Senèze, which the author proposed should be united in a Faunal Unit, marking the beginning of the late Villafranchian; immediately after the latter period, hence within the Olivola Faunal Unit; and at the late Villafranchian–Epivillafranchian transition, which is more elusive to date. In the final part of the article, biochronological correlations based on the reviewed dispersals and faunal turnovers are presented.

Tesakov et al. [2] provide a biochronological scheme based on small mammals, especially arvicolids, for the Plio-Pleistocene of Eastern Turkey and Transcaucasus (Armenia and Azerbaijan). Based on originally collected and reviewed material from the Early Pliocene to the early Middle Pleistocene of sixteen localities, the authors built a stratigraphic chart, enabling correlation with Anatolian and European biozonations. The important events recognized include the following: the Early Pliocene Promimomys stage, the late Ruscinian vole radiation, the Villanyian Mimomys radiation and the dispersal of Borsodia, the Allophaiomys datum at the Villanyian–Biharian transition, and the Microtini radiation at beginning of the Biharian.

Konidaris and Kostopoulos [3] establish for the first time a series of Faunal Units for Greece. The updated information on the taxonomy, stratigraphy, and chronology of Late Pliocene to Middle Pleistocene large mammal successions in the country allowed the authors to define eight Faunal Units (Milia, Dafnero, Gerakarou, Tsiotra Vryssi, Krimni, Apollonia, Marathousa, and Apidima) characterized by first and last occurrences of various taxa. Similarities and correlations with respect to Western Europe (Italy, France, and Spain) are then highlighted and discussed, with major large mammalian faunal turnovers recognized at ca. 2.6–2.5 Ma, 2.0 Ma, 1.7–1.6 Ma, and within the Mid-Pleistocene Revolution.

Konidaris et al. [4] describe new material and review previous findings of mammals from the late Early to Middle Pleistocene deposits of the Megalopolis Basin (Greece), which yielded a long and rather continuous faunal sequence. New discoveries include a new late Early Pleistocene site, Choremi 6, and two partial skeletons of Hippopotamus and Palaeoloxodon from Marathousa 1. Newly discovered small mammals allowed the authors to discuss age constraints for the sites of the Megalopolis Basin, and then their biochronological importance in Greece and Europe. The basin retained freshwater bodies even during glacial stages, as indicated by the occurrence of faunal elements highly dependent on the availability of freshwater (beavers, hippopotamuses, and otters), supporting the view that it acted as a refugium area for several species.

Mecozzi et al. [5] review the Italian fossil record of Middle Pleistocene hippopotamuses, including Hippopotamus antiquus and Hippopotamus amphibius, also presenting previously unpublished material from several localities. Morphological comparisons supported the view that a replacement between H. antiquus and H. amphibius occurred at ca. 0.5 Ma (during MIS 13), though it cannot be ruled out that both species might have been present around that time. Biometric analyses confirm the considerations of previous studies, which indicated that H. antiquus was generally larger than H. amphibius, although the authors observe that remains of H. antiquus dated to ca. 0.6 Ma show a reduced size when compared to older fossils of the same taxon.

Bellucci et al. [6] describe the carnivoran record from the Early Pleistocene of Coste San Giacomo (Italy) and discuss biochronological implications. The site, which is dated at ca. 2.2 Ma and represents the reference for the homonymous Faunal Unit, played an important role in our comprehension of the middle to late Villafranchian faunal turnover and in the development of the “Wolf event” concept. In Italy, Coste San Giacomo documents the first clear occurrence of Canis etruscus (together with Pantalla), the last occurrence of the hyena Pliocrocuta perrieri, and the first of Homotherium latidens.

Iannucci [7] shows that suids were one of the rarest group of artiodactyls in the Pleistocene of Europe and describes suid material from Peyrolles (France), dated at ca. 1.47 Ma. The author rejects the hypothesis that suids were absent from Europe between ca. 1.8 Ma and 1.2 Ma. The “suid gap” case is then taken as an example to highlight and discuss the large uncertainty in investigating the late Early Pleistocene, which is a crucial timespan for early Homo dispersal.

Madurell-Malapeira et al. [8] review the carnivorans from the late Early Pleistocene of the Vallparadís Section (Spain), encompassing the sites of Cal Guardiola and Vallparadís Estació. Several paleobiological, paleoecological, paleobiogeographical, and biochronological considerations on the identified species are discussed, with special emphasis on their relevance within the context of the Early–Middle Pleistocene Transition. The diverse carnivoran fauna of Vallparadís is then compared to that of other Eurasian and African Pleistocene localities, through cluster and ordination analyses. The results point to an overall separation of African, Asian, and European sites, though the Western Asian localities of Dmanisi and ‘Ubeidiya cluster with European localities. The carnivore guild of the Vallparadís Section closely resembles those of other Western European Epivillafranchian localities, especially Untermassfeld and Vallonnet.

Rodríguez-Gómez et al. [9] provide estimates of carrying capacity (considered therein the prey biomass species that can be sustained over time in an ecosystem) and total available biomass based on the herbivore species recognized at the Early Pleistocene sites of Orce, in Spain (Fuente Nueva-3, Barranco León, and Venta Micena). The carrying capacity values are similar for the analyzed faunal assemblages, while Venta Micena appears more productive than the other sites in terms of total available biomass. The estimated values, which represent optimal conditions, are then compared with the relative abundances of species at the sites, allowing the authors to discuss the taphonomical and ecological factors responsible for the observed differences, with emphasis on the implications for hominins.

Fidalgo et al. [10] present a review of Quaternary hippopotamuses from the Iberian Peninsula (Spain and Portugal), covering Early, Middle, and Late Pleistocene localities. More than forty localities with hippopotamuses are considered, denoting a rich regional fossil record, especially for the Early Pleistocene. The authors recognize a delayed appearance of Hippopotamus in the fossil record of the Iberian Peninsula (ca. 1.7 Ma) compared to other European Mediterranean regions (2.2–2.0 Ma; France, Italy, and Greece). They hypothesize a brief coexistence between Hippopatamus antiquus and Hippopotamus amphibius (ca. 0.45 Ma) and suggested that hippopotamus populations went extinct in the Iberian Peninsula between MIS 5 and MIS 3, similar to Italy. Paleoecological considerations, with highlights on pathologies and rare cases of the exploitation of hippopotamuses by hominins, are also discussed.

3. Future Directions

Trans-regional discussions on mammalian biochronology and paleoecology are fundamental to enhance our comprehension of the Quaternary. Several articles of this Special Issue, which was initiated with the aim of promoting such scientific exchange, identified or related their results with/to important moments of faunal turnover that are widely recognized across Europe. However, not all periods and geographic areas are equivalently known, and even for those that we have more data on, there is still much that remains to be understood.

Ultimately, biochronological correlations depend on the reliability of the taxonomic attributions and the dating of the localities from which the faunal elements come from. Therefore, the application of absolute and relative dating methods alternative to and in combination with biochronology—or the cross-correlation of different local/regional biochronological schemes—and the discovery and description of new material—or the reexamination of older/historical collections and refinement of previous taxonomic attributions—will be crucial to improving the correlations at a regional-to-pan-European scale. New systematic fieldwork in well-stratified and dated contexts will ensure reliable paleogeographic, paleoenvironmental, and taphonomic interpretations, while applying modern methods to the revision of older collections (or contextualize the latter in light of recent advancements) will provide further support. Paleoecological information is deeply entwined with biochronology, making integrated studies that address both aspects especially important. Indeed, faunal events that provide data for correlation often document the response of the biota to climatic and environmental changes.

Eventually, a deeper understanding of the recent geological past is critical to gain perspective on ongoing and foreseeable environmental changes, and insights drawn from the mammalian fossil record represent a fundamental source of information.