Pliocene-Pleistocene Boundary Research Articles

Neotectonics and Geological Structure of the Sevan Intermountain Basin (Armenia): New Structural and Paleontological Data

The article presents new data obtained as a result of field research in 2022 Sevan intermountain depression in Armenia. The emergence of the Sevan intermountain depression in the Miocene was associated with the development of the Sevan almond-shaped structure, bounded by the right-lateral Pambak‒Sevan‒Syunik fault zone in the northeast, the Garni zone in the south, and the Arpa‒Zangezur zone in the southwest. Within the Sevan almond-shaped structure, strike-slip structures of Small Sevan (western part of Lake Sevan) and Gavar almond-shaped structure, Gavar horst, a number of faults, as well as extension zones were formed, including the southern part of Greater Sevan (eastern part of Lake Sevan) and axial zone of the Geghama Range. The development of the Sevan intermountain depression continued in the Pliocene under the influence of the uplift of the Lesser Caucasus and the Armenian Highlands. We have summarized the available data on the geological structure and geodynamics of the Sevan intermountain depression, presented the obtained data on the stratigraphy of the Pliocene–Quaternary deposits and their position, and showed that during the Akchagyl transgression at the Pliocene–Pleistocene boundary, sedimentary accumulations did not occur in the Sevan intermountain depression.

Northern Richness, Southern Dead End-Origin and Dispersal Events of Pseudolycoriella (Sciaridae, Diptera) between New Zealand's Main Islands.

Sciaridae (Diptera) is a widespread insect family of which some species can reach high abundances in arboreal habitats. This trait, together with their (passive) mobility, enables them to quickly colonise suitable habitats. To reveal the biogeographic history of the New Zealand members of the sciarid genus Pseudolycoriella, we analysed three molecular markers of selected species and populations in a Bayesian approach. At the intra- and interspecific levels, we detected a pattern of northern richness vs. southern purity, which has probably developed as a result of Pleistocene glacial cycles. Since the late Miocene, we identified 13 dispersal events across the sea strait separating New Zealand's main islands. As nine of these dispersal events were south-directed, North Island can be considered the centre of radiation for this genus. An unequivocal re-colonisation of North Island was only observed once. Based on the inclusion of three undescribed species from Tasmania and on previously published data, three colonisations of New Zealand are likely, all of them assumed to be of Australian origin. One of these most probably took place during the late Miocene, and the other two during the late Pliocene or at the Pliocene-Pleistocene boundary.

Tusked walruses (Carnivora: Odobenidae) from the Miocene–Pliocene Purisima Formation of Santa Cruz, California (U.S.A.): a new species of the toothless walrus Valenictus and the oldest records of Odobeninae and Odobenini

ABSTRACT Currently limited to cold climates near the Arctic circle, living walruses are the sole survivors of a previously much more diverse clade that occupied coastal waters throughout the northern hemisphere during the Mio–Pliocene. Though pinniped faunas have the highest diversity of walruses in the Miocene, the Purisima Formation of California records a moderately diverse assemblage of four walrus species. We report new specimens of tusked walruses (Odobeninae) including the oldest known members of Odobeninae, and Odobenini, and fossils of the specialized toothless odobenine walrus Valenictus Mitchell, 1961. Among these is the new species Valenictus sheperdi sp. nov., represented by a complete skull and referred post-crania from lower Pliocene strata within the Purisima Formation (5.33–4.89 Ma). Additionally, we report a geochronologically younger skull of Valenictus chulavistensis Deméré, 1994 from further up section (4.89–3.59 Ma). Expanded phylogenetic analysis recovers Odobeninae including Ontocetus Leidy, 1859 as the earliest diverging lineage in the Odobenini, and places a monophyletic Valenictus as the sister taxon to Pliopedia, Kellogg, 1921 which is included in a phylogeny for the first time; Odobenus is sister to the Valenictus + Pliopedia clade. Discovery of an isolated metacarpal near the base of the formation provides the oldest known well-dated evidence of odobenines. A diverse assemblage of molluskivores characterized the Neogene eastern North Pacific and their extinction around the Pliocene–Pleistocene boundary coincided with tectonically driven paleogeographic changes on the Pacific coast. The loss of temperate walruses may have provided opportunities for both new molluskivores and the otariid and phocid pinnipeds that make up present North Pacific pinniped communities.

What Does the “Elephant-Equus” Event Mean Today? Reflections on Mammal Dispersal Events around the Pliocene-Pleistocene Boundary and the Flexible Ambiguity of Biochronology

The dispersal of primitive elephantines and monodactyl equids in Eurasia has long been regarded as representative of a substantial turnover in mammal faunas, denoting the spread of open environments linked to the onset of cold and dry conditions in the Northern Hemisphere. During the 1980s, this event was named the “Elephant-Equus event” and it was correlated with the Gauss-Matuyama reversal, today corresponding to the Pliocene-Pleistocene transition and the beginning of the Quaternary, dated at ~2.6 Ma. Therefore, the Elephant-Equus event became a concept of prominent biochronological and paleoecological significance, especially in western Europe. Yet, uncertainties surrounding the taxonomy and chronology of early “elephant” and “Equus”, as well as conceptual differences in adopting (or understanding) the Elephant-Equus event as an intercontinental dispersal event or as a stratigraphic datum, engendered ambiguity and debate. Here, we provide a succinct review of the Elephant-Equus event, considering separately the available evidence on the “elephant” and the “Equus”. Elephantines dispersed out of Africa during the Pliocene (Piacenzian). Their earliest calibrated occurrences from eastern Europe date at ~3.2 Ma and they are usually referred to Mammuthus rumanus, although the allocation of several samples to this species is tentative. Available dating constraints for other localities do not resolve whether the dispersal of Mammuthus was synchronous across Eurasia, but this possibility cannot be ruled out. The spread of Mammuthus was part of an intercontinental faunal exchange between Africa and Eurasia that occurred during the Piacenzian, but in this scenario, Mammuthus is quite unique in being the only genus of African origin dispersing to western Eurasia. The arrival of monodactyl equids from North America coincides with the Pliocene-Pleistocene transition, with several occurrences dated or calibrated at ~2.6 Ma and no compelling evidence prior to this age. In Europe, early monodactyl equids are often aligned to Equus livenzovensis, but the material from the type locality of this species is chronologically time-averaged and taxonomically heterogeneous, and western European samples are seldom abundant or informative. Regardless, this does not diminish the biochronological significance of the “Equus event”. Indeed, while the term “Elephant-Equus event” should no longer be used, as the appearance of elephantines in the European fossil record markedly precedes that of monodactyl equids, we endorse the use of the “Equus event” as a valid alternative to refer to the intercontinental dispersal event that characterizes the middle Villafranchian faunal turnover, epitomized by but not limited to monodactyl equids.

Reference-Based RADseq Unravels the Evolutionary History of Polar Species in 'the Crux Lichenologorum' Genus Usnea (Parmeliaceae, Ascomycota).

Nearly 90% of fungal diversity, one of the most speciose branches in the tree of life, remains undescribed. Lichenized fungi as symbiotic associations are still a challenge for species delimitation, and current species diversity is vastly underestimated. The ongoing democratization of Next-Generation Sequencing is turning the tables. Particularly, reference-based RADseq allows for metagenomic filtering of the symbiont sequence and yields robust phylogenomic trees of closely related species. We implemented reference-based RADseq to disentangle the evolution of neuropogonoid lichens, which inhabit harsh environments and belong to Usnea (Parmeliaceae, Ascomycota), one of the most taxonomically intriguing genera within lichenized fungi. Full taxon coverage of neuropogonoid lichens was sampled for the first time, coupled with phenotype characterizations. More than 20,000 loci of 126 specimens were analyzed through concatenated and coalescent-based methods, including time calibrations. Our analysis addressed the major taxonomic discussions over recent decades. Subsequently, two species are newly described, namely U. aymondiana and U. fibriloides, and three species names are resurrected. The late Miocene and Pliocene-Pleistocene boundary is inferred as the timeframe for neuropogonoid lichen diversification. Ultimately, this study helped fill the gap of fungal diversity by setting a solid backbone phylogeny which raises new questions about which factors may trigger complex evolutionary scenarios.

Evolutionary history of Nasutitermes kemneri (Termitidae, Nasutitermitinae), a termite from the South American diagonal of open formations

Little is known about the phylogeography of termites in the Neotropical region. Here, we explored the genetic patterns and phylogeographical processes in the evolutionary history of Nasutitermes kemneri, an endemic termite of the South American diagonal of open formations (DOF) formed by the Chaco, Cerrado, and Caatinga phytogeographic domains. We sampled 60 individuals across the three domains of the DOF, and using the mitochondrial genes 16S, COI, and COII, as well as the nuclear gene ITS, evaluated the genetic diversity and divergence time of the populations, along with their genetic structure. The results show a strong genetic and spatial structure within the samples, evidencing the existence of two well-differentiated genetic groups: the Northeastern and the Southwestern populations, which diverged about 2.5 Mya, during the Pliocene-Pleistocene boundary. The Northeastern population, which encompasses Caatinga and northern portions of Cerrado, has an intricate structure and seems to have suffered repetitive retraction-expansion events due to climactic fluctuations during the Quaternary. The Southwestern population, which ranges from central-south Cerrado to the northeast peripherical portions of the Chaco, displays a star-shaped haplotype structure, indicating that this region may have acted as a refugia during interglacial periods.

Contrasting continental patterns of adaptive population divergence in the holarctic ectomycorrhizal fungus Boletus edulis.

In the hyperdiverse fungi, the process of speciation is virtually unknown, including for the > 20 000 species of ectomycorrhizal mutualists. To understand this process, we investigated patterns of genome-wide differentiation in the ectomycorrhizal porcini mushroom, Boletus edulis, a globally distributed species complex with broad ecological amplitude. By whole-genome sequencing 160 individuals from across the Northern Hemisphere, we genotyped 792 923 single nucleotide polymorphismsto characterize patterns of genome-wide differentiation and to identify the adaptive processes shaping global population structure. We show that B. edulis exhibits contrasting patterns of genomic divergence between continents, with multiple lineages present across North America, while a single lineage dominates Europe. These geographical lineages are inferred to have diverged 1.62-2.66 million years ago, during a period of climatic upheaval and the onset of glaciation in the Pliocene-Pleistocene boundary. High levels of genomic differentiation were observed among lineages despite evidence of substantial and ongoing introgression. Genome scans, demographic inference, and ecological niche models suggest that genomic differentiation is maintained by environmental adaptation, not physical isolation. Our study uncovers striking patterns of genome-wide differentiation on a global scale and emphasizes the importance of local adaptation and ecologically mediated divergence, rather than prezygotic barriers such as allopatry or genomic incompatibility, in fungal population differentiation.

Hypogene speleogenesis related to porphyry magmatic intrusions and its influence on subsequent karst evolution in the Peruvian high Andes

Carbonate rocks of Cretaceous and Jurassic age are widespread in the Peruvian Andes where they host numerous magmatic intrusions and related ore deposits. Most of Peru's metal ore deposits are located at high elevations within a narrow, tectonized carbonate-rock belt extending over 2000 km in length. Many of the limestone formations are karstified and characterized by high recharge and percolation rates, well-developed subsurface drainage and complex flow patterns. Knowledge of karst in the Andes is generally limited, although karst is recognized to cause extreme hydrogeologic complexity and great challenges in development of mining facilities located in carbonate settings. Aspects of the origin of void/conduit systems (i.e. speleogenesis) and karst evolution are rarely addressed in environmental impact and risk assessment studies.This study in the Antamina area in the east side of the Cordillera Occidental, home to the world largest known skarn copper‑zinc deposit, demonstrates that the current karst system has formed as the result of polygenetic and multi-phase development. Structure-controlled hypogene cave systems are well-preserved and widespread in the area and present a foremost example of endogenous hypogene speleogenesis related to magmatic intrusions. Hypogene karst structures have strongly influenced subsequent epigene karstification, which commenced at the Pliocene-Pleistocene boundary. Changes in the base-level position due to the landscape evolution and Pleistocene glaciations were major additional factors that influenced epigene karst development. The findings of this study are potentially relevant to assessing karst origin and hydrogeology in many carbonate-hosted ore deposits in the Peruvian Andes and other regions. This study shows that the speleogenetic and evolutionary approach is indispensable in the development of sound conceptual models of groundwater flow in karst terrains and the assessment of karst-related hazards and risks.

The state of knowledge of the jaguar Panthera onca (Linnaeus, 1758) (Carnivora, Felidae) during the Quaternary in Uruguay

Felids are the top predators in the environments they inhabit. They entered South America at the Pliocene-Pleistocene boundary, but their fossil record in Uruguay, although informative, is scarce. In the present contribution, three new materials (two hemimandibles and an isolated first lower molar) assigned to Panthera onca (Linnaeus, 1758) are described. This material came from Quaternary sediments (Sopas, Dolores, and Libertad Formations) from several localities in Uruguay. Based on this material, different aspects of the paleobiology and paleoecology of jaguars are discussed. Remains of these felids were previously listed but never described; thus, the material analyzed here is the first fossil records reliably determined for P. onca in Uruguay. These felids would have shared an ecological niche with other large carnivores during the late Pleistocene in Uruguay, such as saber-toothed cats (Smilodon populator Lund, 1842; S. fatalis Leidy, 1868), Puma concolor Linnaeus, 1771, and short face bears Arctotherium Burmeister, 1879; and they would have fed upon medium-sized herbivores, principally in vegetated environments.

Palynostratigraphy indication of the Pliocene–Pleistocene boundary in Hupo Basin of the East Sea, offshore Korea

Palynostratigraphy indication of the Pliocene–Pleistocene boundary in Hupo Basin of the East Sea, offshore Korea

A tribute to Menke (1970): Results of pollen analysis on the Pleistocene stratigraphy and the Pliocene–Pleistocene boundary in Schleswig-Holstein

A tribute to Menke (1970): Results of pollen analysis on the Pleistocene stratigraphy and the Pliocene–Pleistocene boundary in Schleswig-Holstein

Results of pollen analysis on the Pleistocene stratigraphy and the Pliocene-Pleistocene boundary in Schleswig-Holstein

Results of pollen analysis on the Pleistocene stratigraphy and the Pliocene-Pleistocene boundary in Schleswig-Holstein

Demographic history and genetic diversity of wild African harlequin quail (Coturnix delegorguei delegorguei) populations of Kenya.

Hunting wild African harlequin quails (Coturnix delegorguei delegorguei) using traditional methods in Western Kenya has been ongoing for generations, yet their genetic diversity and evolutionary history are largely unknown. In this study, the genetic variation and demographic history of wild African harlequin quails were assessed using a 347bp mitochondrial DNA (mtDNA) control region fragment and 119,339 single nucleotide polymorphisms (SNPs) from genotyping‐by‐sequencing (GBS) data. Genetic diversity analyses revealed that the genetic variation in wild African harlequin quails was predominantly among individuals than populations. Demographic analyses indicated a signal of rapid demographic expansion, and the estimated time since population expansion was found to be 150,000–350,000 years ago, corresponding to around the Pliocene–Pleistocene boundary. A gradual decline in their effective population size was also observed, which raised concerns about their conservation status. These results provide the first account of the genetic diversity of wild African harlequin quails of Siaya, thereby creating a helpful foundation in their biodiversity conservation.

The Oldest Species of Dolichotis (Rodentia, Hystricognathi) from the Pliocene of Argentina: Redescription and Taxonomic Status of “Orthomyctera” chapalmalense

The Subfamily Dolichotinae comprises two living species, Dolichotis patagonum, an emblematic component of the Patagonian fauna of Argentina, and Dolichotis salinicola, endemic to the Chaco ecoregion. These two species are also considered as pertaining to different genera, D. patagonum and Pediolagus salinicola. The oldest records of Dolichotis come from the Pliocene–Pleistocene boundary of northeastern and central Argentina, and the late Pleistocene from southern Brazil, and northern and southern Uruguay. Five fossil species were described from the Pleistocene and Holocene in central Argentina (D. minor, D. plathycephala, D. major, D. intermedia, and D. improla). “Orthomyctera” chapalmalense was described on the basis of remains from the coast of Mar del Plata and Chapadmalal, Buenos Aires Province, Chapadmalal Formation (late Pliocene, 3.74–3.04 Ma). A new detailed description of the holotype and its comparison with closely related taxa suggests that this species is more related to the genus Dolichotis, resulting in the new combination D. chapalmalense. The close affinities with Dolichotis revealed by phylogenetic analyses combined with molecular and morphological characters were corroborated in previous analyses. The origin of this lineage extends at least to a million years ago, taking the record back to the middle Pliocene. The evolutionary novelties that appear at least since the Pliocene, marking a key period for the Caviidae, are analyzed. Based on a phylogenetic perspective with the inclusion of the fossil record, our data support the inclusion of the two species (D. patagonum and D. salinicola) in a single genus.

Oblique plate collision and orogenic translation of the Southern Apennines revealed by post-Messinian interregional unconformities in the Bradano Basin (Ionian Sea - Central Mediterranean)

The Bradano Basin is a foreland basin along the Africa/Eurasia plate boundary. Due to its location and physiography, between Southern Apennines (SA) and Calabrian Arc (CA), it represents a natural recorder of Plio-Pleistocene tectonic processes. Integrated analysis of seismic reflection data, exploration well logs and seafloor bathymetry allowed us to unravel the basin architecture and the interplay between tectonics and sedimentation, providing stratigraphic and structural evidences on deep processes and shallow morpho-structural development. It results, that the post-Messinian tectonic evolution on this area is marked by two major tectonic events, whose effects are recorded in four sedimentary sequences bounded by interregional unconformities. During Pliocene times, an obliquely convergent margin led to collision between SA and CA, associated with shelf to deep marine turbiditic deposits. Around the Pliocene-Pleistocene boundary (2.58 Ma), a sudden and widespread rearrangement took place. The SA front, along with portions of the earlier obliquely collisional margin, started to move toward the NE, along progressively deeper detachments involving the lower Apulia plate. During this phase, a fast (3.8–8.3 cm/yr) ~50 km translation of the orogenic wedge was followed by uplift and slow-rate shortening (1.9 mm/year), associated with seafloor folding. This second phase is marked by deep marine deposits in the central part of the basin, and clinoforms in shallower western and northern sectors. Our data suggest that no oceanic crust is presently subducting below the Bradano Basin, although we cannot exclude that a narrow sliver of oceanic lithosphere was subducted before and/or during Pliocene times. The complex deformation pattern observed, represents the response to the interaction of (small-) plates, which is still active and important to be considered in neotectonics and paleoseismological reconstructions.

Phylogenetic relationships among Callosciurus squirrels in the Indochina Peninsula: phylogenetic position of C. pygerythrus from Myanmar

The phylogenetic relationships among seven Callosciurus species from the Indochina Peninsula, including the C. honkhoaiensis which is endemic to Hon Khoai Island, were studied using complete mitochondrial cytochrome b gene sequences (1140 bases). We primarily focused on the phylogenetic position of C. pygerythrus, which is distributed in the western part of the peninsula. We identified two main lineages: 1) C. caniceps, C. honkhoaiensis, C. inornatus, C. phayrei and C. pygerythrus, and 2) C. erythraeus and C. finlaysonii. Estimated divergence time between the two lineages was at the junction of the Zanclean and Piacenzian in the Pliocene. Within the first linage, the divergence time of sub-lineages corresponded to the Pliocene-Pleistocene boundary, although phylogenetic relationships were unclear. These two divergence times estimated in the present study correspond to episodes of global cooling, suggesting that climate may have contributed to the divergence of these Callosciurus squirrels.

Pan-American Trypanosoma (Megatrypanum) trinaperronei n. sp. in the white-tailed deer Odocoileus virginianus Zimmermann and its deer ked Lipoptena mazamae Rondani, 1878: morphological, developmental and phylogeographical characterisation

BackgroundThe subgenus Megatrypanum Hoare, 1964 of Trypanosoma Gruby, 1843 comprises trypanosomes of cervids and bovids from around the world. Here, the white-tailed deer Odocoileus virginianus (Zimmermann) and its ectoparasite, the deer ked Lipoptena mazamae Rondani, 1878 (hippoboscid fly), were surveyed for trypanosomes in Venezuela.ResultsHaemoculturing unveiled 20% infected WTD, while 47% (7/15) of blood samples and 38% (11/29) of ked guts tested positive for the Megatrypanum-specific TthCATL-PCR. CATL and SSU rRNA sequences uncovered a single species of trypanosome. Phylogeny based on SSU rRNA and gGAPDH sequences tightly cluster WTD trypanosomes from Venezuela and the USA, which were strongly supported as geographical variants of the herein described Trypanosoma (Megatrypanum) trinaperronei n. sp. In our analyses, the new species was closest to Trypanosoma sp. D30 from fallow deer (Germany), both nested into TthII alongside other trypanosomes from cervids (North American elk and European fallow, red and sika deer), and bovids (cattle, antelopes and sheep). Insights into the life-cycle of T. trinaperronei n. sp. were obtained from early haemocultures of deer blood and co-culture with mammalian and insect cells showing flagellates resembling Megatrypanum trypanosomes previously reported in deer blood, and deer ked guts. For the first time, a trypanosome from a cervid was cultured and phylogenetically and morphologically (light and electron microscopy) characterised.ConclusionsIn the analyses based on SSU rRNA, gGAPDH, CATL and ITS rDNA sequences, neither cervids nor bovids trypanosomes were monophyletic but intertwined within TthI and TthII major phylogenetic lineages. One host species can harbour more than one species/genotype of trypanosome, but each trypanosome species/genotype was found in a single host species or in phylogenetically closely related hosts. Molecular evidence that L. mazamae may transmit T. trinaperronei n. sp. suggests important evolutionary constraints making tight the tripartite T. trinaperronei-WTD-deer ked association. In a plausible evolutionary scenario, T. trinaperronei n. sp. entered South America with North American white-tailed deer at the Pliocene-Pleistocene boundary following the closure of the Panama Isthmus.

Species delimitation and evolutionary relationships among Phoebis New World sulphur butterflies (Lepidoptera, Pieridae, Coliadinae)

ABSTRACTThe most accepted taxonomic treatment of the New World sulphurs of the genus Phoebis Hübner, [1819] recognizes 16 species including those in the current synonyms Aphrissa and Rhabdodryas. This total conflicts with the results of several recent pierid DNA barcode studies across the Neotropics. We used a five‐locus dataset to carry out species delimitation analyses using the coalescence‐based method implemented in bpp software. After testing the resulting species hypotheses using marginal likelihood estimates, we inferred their phylogenetic relationships and performed an ancestral range reconstruction with biogeobears. Our analyses recovered two different hypotheses, 26 and 24 species, that scored the highest marginal likelihood estimate. Differences between these two hypotheses, when reconciled with barcode clusters and morphology, indicated that 24 is the most likely number of species. Phoebis neocypris stat. rev., Phoebis rurina stat. rev., Phoebis virgo stat. rev., Phoebis marcellina stat. rev., Phoebis thalestris stat. rev., and Phoebis rorata stat. rev. are raised to the species rank. We dated the crown age of Phoebis to the mid‐Miocene, with the islands of the Greater Antilles as the most probable ancestral range. Three main clades of Phoebis diverged early in the evolutionary history of the genus, but most extant species‐level diversity arose after the Pliocene–Pleistocene boundary. Our analyses recovered alternate range expansions and contractions, and dispersal from the islands to the continent and back, in the three main clades. Both sympatric and allopatric speciation seem to have shaped the current species richness.

A constant Chinese Loess Plateau dust source since the late Miocene

The Pliocene-Pleistocene boundary marks a major change in global climate and East Asian monsoon dynamic. However, the role of the global atmospheric dust-cycle over this time is unclear; in particular the degree to which changes in the dust cycle influenced climate change, were driven by climate change, and how these processes interacted. Chinese loess records past dust-cycle history and the influences of aridification and monsoon circulation over the last 40 Ma. Previous work on the Chinese Loess Plateau argue over whether changes in dust source occur at the Pliocene-Pleistocene boundary, or at 1.2 Ma, despite these intervals marking major shifts in monsoon dynamics. We present Sr, Nd and Hf isotope data from multiple sites and show that dust source largely remains unchanged across these boundaries. Shifts in geochemistry are due to changes in grain-size and weathering. While the transport pathway (river, deserts, direct aeolian) is unclear, these tracer isotopes show that dust was dominantly sourced from the Northern Tibetan Plateau, with some input from the local bedrock. This shows that a major established and constant dust source on the Tibetan Plateau has been active and unchanged since late Miocene, despite dramatically changing climate conditions. Changes in loess accumulation are a function of climate change in Tibetan Plateau source regions rather than effects from increased aridification over the Pliocene-Pleistocene boundary.

Bio- and lithostratigraphy of lower Pleistocene marine successions in western Emilia (Italy) and their implications for the first occurrence of Arctica islandica in the Mediterranean Sea

AbstractThe Arda and Stirone marine successions (Italy) represent key sections for the early Pleistocene; they were deposited continuously within a frame of climate change, recording the Calabrian cooling as testified by the occurrence of the “northern guests,” such as the bivalve Arctica islandica. In addition, although the first occurrence of A. islandica in the Mediterranean Sea was used as the main criterion to mark the former Pliocene-Pleistocene boundary, the age of this bioevent was never well constrained. Here, we describe the Stirone depositional environment and constrain for the first time the section age using calcareous nannofossil and foraminifera biostratigraphy. We also correlate the Arda and Stirone sections using complementary biostratigraphic and magnetostratigraphic data. Our results indicate that A. islandica first occurred in both the successions slightly below the top of the CNPL7 biozone (dated at 1.71 Ma). Comparisons with other lower Pleistocene Mediterranean marine successions indicate that the stratigraphically lowest level where A. islandica first occurred in the Mediterranean Sea is in the Arda and Stirone sections; these environments satisfied the ecological requirements for the establishment and the proliferation of the species, which only subsequently (late Calabrian) has been retrieved in southern Italy and other areas of the Mediterranean Sea.