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Neogene

The Neogene Period is the second period of the Cenozoic Era, spanning from 23.03 million years ago to 2.58 million years ago, and is marked by a global cooling trend that led to the widespread expansion of grasslands at the expense of forests, alongside significant tectonic activity and the evolutionary diversification of mammals into forms resembling modern species.^[1]^[2]^[3] This period encompasses profound changes in Earth's biomes, with the closure of ancient seaways and uplift of mountain ranges driving shifts in ocean currents and atmospheric circulation, ultimately setting the stage for the Pleistocene ice ages.^[1]^[4] The Neogene is formally divided into two epochs: the Miocene Epoch, from 23.03 to 5.33 million years ago, and the Pliocene Epoch, from 5.33 to 2.58 million years ago.^[1]^[2] During the Miocene, extensive mountain-building events occurred, including the uplift of the Cascade and Coast Ranges in North America, the activation of the San Andreas Fault, and massive volcanic outpourings such as the Columbia River Basalts, which covered an area of about 210,000 square kilometers (81,000 square miles) to thicknesses of up to 3 kilometers (10,000 feet).^[1]^[5] In the Pliocene, further uplifts shaped the Sierra Nevada, Rocky Mountains, and Colorado Plateau, while the formation of the Isthmus of Panama around 3 million years ago connected North and South America, facilitating the Great American Biotic Interchange of species.^[1]^[2] Climatically, the Neogene witnessed a progressive cooling and drying, with temperatures dropping gradually from warmer Miocene conditions to cooler Pliocene environments, influenced primarily by tectonic events such as the Himalayan orogeny and the restriction of the Tethys Sea.^[1]^[4] This led to the decline of tropical forests and the rise of open savannas and steppes, with C4 grasslands expanding rapidly in the late Miocene due to lower CO2 levels and increased seasonality.^[3]^[6] Biologically, the Neogene saw the radiation of placental mammals, including the evolution of grazing herbivores like horses (culminating in the modern genus Equus in the Pliocene), camels, rhinoceroses, and early proboscideans such as mastodons, alongside carnivores like cats and weasels.^[1]^[7] Flora shifted toward dominance by grasses, with woody plants like elms and hackberries persisting in remnant woodlands, and the first kelp forests appearing in coastal waters during the Miocene.^[1]^[7]^[2] In marine realms, diverse cetaceans and the giant shark Carcharodon megalodon thrived before declining amid cooling oceans.^[2] Notably, the period marks the early evolution of hominids, with ancestral primates appearing in Africa and Asia during the Miocene, laying the groundwork for later human lineages.^[1]

Geological Framework

Definition and Boundaries

The Neogene Period represents the second period of the Cenozoic Era in the geologic time scale, succeeding the Paleogene and preceding the Quaternary. It encompasses a temporal span from approximately 23.04 million years ago (Ma) to 2.58 Ma, covering about 20.45 million years of Earth history.^[8] This interval is characterized by significant global cooling, the continued diversification of modern ecosystems, and major tectonic reorganizations that shaped contemporary continental configurations. The International Commission on Stratigraphy (ICS) defines the Neogene based on a combination of biostratigraphic, magnetostratigraphic, and chemostratigraphic criteria to ensure global correlation of rock successions.^[9] The term "Neogene" was coined in 1853 by Austrian paleontologist Moritz Hörnes to designate a post-Eocene interval grouping the Miocene and Pliocene epochs, reflecting observed similarities in their fossil assemblages, particularly marine invertebrates.^[9] This nomenclature emphasized a "new" generation of life forms distinct from earlier Cenozoic faunas, and it gained widespread adoption in European stratigraphy by the late 19th century. Over time, the ICS refined the term's scope to exclude the Quaternary, aligning it with formal chronostratigraphic standards that prioritize objective boundary definitions over historical regional usages.^[10] The base of the Neogene coincides with the Oligocene-Miocene boundary, formally defined by the Global Stratotype Section and Point (GSSP) at the Lemme-Carrosio section in northern Italy, where it is marked by the first appearance of the planktonic foraminifer Paragloborotalia kugleri (synonym Globorotalia kugleri), supplemented by calcareous nannofossil datums including the first appearance of Sphenolithus ciperoensis and a carbon isotope excursion.^[11]^[12] This biostratigraphic criterion, correlated via magnetostratigraphy to Chron C6Cn, ensures precise global recognition. The top boundary is placed at the base of the Gelasian Stage (lowermost Quaternary), with its GSSP at Monte San Nicola in Sicily, Italy, defined at the base of a marly layer 62 meters above the section base, coinciding closely with the Gauss-Matuyama magnetic polarity reversal (Chron C2r base) at approximately 2.58 Ma, and supported by nannofossil and foraminiferal bioevents such as the last occurrence of Discoaster pentaradiatus.^[13] On continental margins, biostratigraphic correlation often relies on mammalian faunas, such as the European Mammal Neogene (MN) zones, which track evolutionary turnovers in taxa like proboscideans and equids to align with marine standards.^[10] These boundaries facilitate high-resolution integration of marine and terrestrial records across the period.

Subdivisions

The Neogene Period is formally subdivided into two epochs: the Miocene (23.04–5.333 Ma) and the Pliocene (5.333–2.58 Ma).^[14] The Miocene spans approximately 17.7 million years, while the Pliocene lasts about 2.75 million years, with these durations established through a combination of radiometric dating and astronomical tuning of sedimentary cycles.^[14]^[15] The Miocene Epoch is further divided into six stages, from oldest to youngest: Aquitanian (23.04–20.45 Ma), Burdigalian (20.45–15.98 Ma), Langhian (15.98–13.82 Ma), Serravallian (13.82–11.63 Ma), Tortonian (11.63–7.246 Ma), and Messinian (7.246–5.333 Ma).^[14] These stages represent progressive phases of early to late Miocene time, characterized by varying rates of global cooling and tectonic activity, though their primary definition relies on stratigraphic boundaries rather than environmental shifts.^[14] The Pliocene Epoch comprises two stages: Zanclean (5.333–3.600 Ma) and Piacenzian (3.600–2.58 Ma).^[14] The Zanclean marks the initial post-Messinian transgression following the Miocene-Pliocene boundary, while the Piacenzian encompasses the later Pliocene with intensifying Northern Hemisphere glaciation toward its close.^[14] Recognition of Neogene subdivisions depends on global stratotype sections and points (GSSPs) and biostratigraphic zones. For instance, the base of the Miocene (Aquitanian Stage and Neogene Period) is defined at the GSSP in the Lemme-Carrosio section, Alessandria Province, Italy, approximately 35 m from the top of the section, correlated with the base of magnetic polarity Chron C6Cn.^[16]^[17] Biostratigraphic criteria include calcareous nannofossil zones, such as the first appearance of Sphenolithus ciperoensis near the Oligocene-Miocene boundary, and diatom zones, like the lowest occurrence of Crucidenticula kanayae for the upper Burdigalian Stage, which provide high-resolution correlation in marine sediments.^[18]^[12] These markers, integrated with magnetostratigraphy and chemostratigraphy, ensure global consistency in stage boundaries.^[14]

Physical and Environmental Setting

Paleogeography

During the Neogene Period, the global paleogeography transitioned toward modern continental configurations, marking the culmination of the supercontinent Pangaea's breakup initiated in the Mesozoic. By the early Miocene, the major landmasses had largely achieved their present relative positions, with Laurasia and Gondwana fully fragmented into the Americas, Eurasia, Africa, India, Australia, and Antarctica. Paleogeographic reconstructions illustrate this stage as one of relative stability in broad outlines, though regional adjustments persisted due to plate motions.^[19]^[20] In the mid-Miocene, around 15–14 million years ago (Ma), the ongoing convergence of the Indian plate with Eurasia intensified the closure of the eastern Neo-Tethys Ocean, promoting the uplift of the Himalayan orogen as a remnant of the initial Eocene collision. This process reduced the Tethys seaway's extent, transitioning it from a broad equatorial gateway to fragmented basins. Concurrently, Australia's northward drift, following its Eocene separation from Antarctica, positioned it closer to Southeast Asia, facilitating the establishment of the Southern Ocean's full extent between the two continents.^[21] From the late Miocene to the Pliocene, significant gateway restrictions reshaped ocean-continent interactions. The northward migration of the African plate narrowed the connection between the Atlantic and the Mediterranean, culminating in the temporary closure of the Gibraltar Strait around 5.96–5.33 Ma during the Messinian stage, isolating the Mediterranean Basin. Approximately 3 Ma, in the early Pliocene, tectonic uplift formed the Isthmus of Panama, linking North and South America and severing the direct Central American seaway between the Atlantic and Pacific Oceans.^[22] Throughout the Neogene, ocean basin dynamics reflected continued divergence and convergence. The Atlantic Ocean widened progressively via seafloor spreading along the Mid-Atlantic Ridge, expanding from about 3,000 km in the early Miocene to nearly its modern average width of about 3,700 km by the Pliocene. In contrast, the Pacific Ocean experienced ongoing subduction along its margins, particularly in the Ring of Fire, where the Pacific Plate was consumed beneath the North American, Eurasian, and Indo-Australian plates, contributing to arc volcanism and trench deepening. These changes, depicted in serial paleogeographic maps, underscore the Neogene as a period of refinement in global geography, with Pangaea's dispersed fragments stabilizing into the framework observed today.^[23]^[24]^[20]^[25]

Tectonic Developments

The Neogene period witnessed significant intensification of the Alpine-Himalayan orogeny, driven by ongoing convergence between the African and Eurasian plates following the closure of the Neo-Tethys Ocean. This collisional process, which began in the Paleogene, accelerated during the Miocene, leading to enhanced crustal shortening and thickening across the orogenic belt from the Mediterranean to Southeast Asia. In the Himalayan sector, the convergence resulted in the southward propagation of thrust belts and the exhumation of deep-seated rocks, with major deformation episodes recorded between approximately 23 and 5 million years ago (Ma).^[26] A key outcome was the uplift of the Tibetan Plateau, particularly between ~10 and 5 Ma, where rapid elevation gain of several kilometers occurred due to distributed shortening and lower crustal flow, as evidenced by thermochronological and sedimentary records.^[27] In the western segment, the Zagros Mountains formed through southwest-verging folds and thrusts linked to the subduction and obduction of Neo-Tethyan remnants, with peak activity in the late Miocene to Pliocene.^[28] Similarly, the Andean orogeny experienced accelerated development during the Neogene, primarily due to changes in the subduction dynamics of the Nazca plate beneath the South American plate. Following an abrupt increase in convergence rate to about 15 cm/year around 25–23 Ma, the orogen transitioned to more trench-normal subduction, focusing shortening eastward into the Eastern Cordillera and sub-Andean foreland basins between 25 and 11 Ma.^[29] This phase shaped the modern Andean topography, with Miocene flat-slab subduction episodes (e.g., 18–12 Ma in the Puna Plateau) causing widespread crustal thickening and the emplacement of igneous bodies, culminating in the high-elevation cordilleras observed today. Paleomagnetic and stratigraphic data indicate that subduction obliquity decreased post-25 Ma, enhancing compressional deformation and contributing to the Andes' present configuration spanning over 7,000 km.^[30] Neogene tectonics also featured prominent basin formation through rifting and extension. In East Africa, precursors to the modern Great Rift Valley emerged as part of the East African Rift System (EARS), with initial rifting in the mid-late Miocene (~13 Ma) forming small depressions and basins between Ethiopia and Malawi, followed by main subsidence in the Pliocene (~5 Ma).^[31] The Eastern Branch initiated around 5 Ma in the Main Ethiopian Rift, while the Western Branch began ~13 Ma in the Albertine Basin, characterized by fault-bounded grabens and half-grabens that deepened progressively southward, with peak activity in the last 1–2 Ma. Back-arc basins in the western Pacific, such as the Sulu and Celebes basins, opened during the early Miocene (~23–16 Ma) in response to subduction along the Philippine and Ryukyu arcs, involving extension behind volcanic arcs and subsequent partial closure by late Miocene compression.^[32] Volcanism associated with intraplate hotspots and subduction zones was widespread in North America during the Neogene. The Yellowstone hotspot, active since ~16 Ma, produced a northeast-trending track of silicic caldera-forming eruptions, including the Twin Falls (~10 Ma) and Picabo (~10.2 Ma) volcanic fields in Idaho, followed by the Heise field (~6.7 Ma), as the North American plate migrated over the fixed mantle plume.^[33] This activity extruded over 6,500 km³ of rhyolitic material by ~2 Ma upon reaching the Yellowstone Plateau, influencing regional faulting and uplift. Concurrently, the Cascade Range experienced subduction-related volcanism from the Miocene onward, with the Juan de Fuca plate's northeastward subduction beneath North America driving the formation of stratovolcanoes and mafic eruptions, including early Miocene basaltic andesites that built the arc's foundational framework.^[34] Plate motion rates during the Neogene, reconstructed from paleomagnetic data, highlight the sustained but moderated convergence in key regions. For India-Eurasia, post-collisional motion shifted to NNE-directed convergence at rates of approximately 4–5 cm/year since ~19 Ma, slower than Paleogene velocities but sufficient to accommodate ongoing Himalayan indentation and Tibetan uplift.^[35] These rates, derived from Euler pole analyses and magnetic anomaly correlations, underscore the transition to more oblique subduction in the Nazca-South America system, averaging approximately 10–12 cm/year during the Miocene before deceleration in the Pliocene. Such kinematics provided the dynamic framework for the period's major orogenic and extensional events.^[36]

Climate Dynamics

Global Trends

The Neogene period was characterized by a progression from early warmth to overall cooling, with atmospheric CO₂ levels playing a pivotal role in driving these shifts, as evidenced by multiple proxy records spanning approximately 23 to 2.6 million years ago (Ma). This global narrative highlights intervals of climatic optima interspersed with transitions toward a cooler "icehouse" state, influencing ice volume, sea levels, and temperature gradients. The Early Miocene Climatic Optimum (~17–14 Ma) marked a zenith of Neogene warmth, with global mean surface temperatures approximately 3–4°C higher than today and substantially reduced polar ice sheets, including minimal Antarctic ice coverage.^[37] This episode reflected elevated greenhouse conditions that minimized equator-to-pole thermal contrasts.^[38] A pronounced cooling ensued in the Middle to Late Miocene, culminating in the Middle Miocene Climate Transition (~14 Ma), which initiated widespread Antarctic glaciation and a step toward bipolar ice sheets.^[39] This trend was closely tied to a decline in atmospheric CO₂ from ~500 ppm during the Miocene Climatic Optimum to ~300 ppm by the late Miocene, reducing greenhouse forcing and enabling ice expansion.^[40] The Pliocene featured a temporary reversal with the Mid-Pliocene Warm Period (~3.3–3 Ma), when global temperatures were ~2–3°C warmer than present, sea levels stood 20–25 m higher due to partial deglaciation, and temperate forests advanced into subpolar regions.^[41]^[42]^[43] Reconstructions of these trends rely on proxy indicators such as oxygen isotope ratios (\delta^{18}O) in benthic and planktonic foraminifera, which integrate signals of sea surface temperatures, salinity, and global ice volume.^[44] Complementary terrestrial data come from leaf margin analysis of fossil angiosperm leaves, where the proportion of untoothed margins inversely correlates with mean annual temperature, enabling estimates of continental paleotemperatures.^[45] The overarching CO₂ drawdown, from Miocene peaks above 500 ppm to Pliocene levels around 300–400 ppm, was amplified by intensified silicate weathering in tectonically uplifted mountain belts, which enhanced chemical breakdown of continental rocks and acted as a long-term carbon sink.^[40]^[46]

Regional and Oceanic Influences

The closure of the Panama Isthmus around 3 million years ago marked a pivotal reconfiguration of global ocean circulation, facilitating the Great American Biotic Interchange between North and South America while strengthening the Gulf Stream. This event enhanced poleward heat and moisture transport in the North Atlantic, contributing to a stepwise cooling of deep waters by approximately 2°C between 2.94 and 2.81 Ma, as evidenced by benthic δ¹⁸O records. The intensified North Atlantic thermohaline circulation increased moisture supply to high northern latitudes, ultimately supporting the onset of Northern Hemisphere glaciation around 2.74 Ma.^[47] The Messinian Salinity Crisis, spanning 5.96 to 5.33 Ma, transformed the Mediterranean into a hypersaline basin through restricted inflow from the Atlantic, leading to widespread evaporite deposition and extreme desiccation. This resulted in a profound sea-level drop within the Mediterranean estimated at 600–2100 m (varying by region and model), though estimates vary widely due to modeling differences and proxy interpretations, with recent studies (as of 2024) suggesting values around 1 km or more based on restored paleotopography of incised river canyons like the Nile.^[48]^[49]^[50]^[51] The crisis induced global eustatic effects, including enhanced river incisions and sediment flux changes worldwide, though the precise volume of evaporites suggests a more modest global sea-level lowering on the order of 10–50 m. Hypersaline conditions eradicated much of the marine biota, creating isolated brine pockets and altering regional hydroclimate dynamics. The full opening of the Southern Ocean gateways, particularly the Tasmanian Gateway and Drake Passage around 30 Ma at the Eocene-Oligocene boundary, initiated the Antarctic Circumpolar Current and set the stage for Neogene intensification of thermohaline circulation. During the Neogene, progressive deepening of these gateways weakened subtropical gyres, reducing heat transport to Antarctic margins and promoting polar cooling of 2–5°C along coastal regions. This reconfiguration enhanced deep-water formation and global ocean ventilation, amplifying the overall Neogene cooling trajectory through strengthened meridional overturning.^[52]^[53] In Asia, the ongoing uplift of the Himalayan-Tibetan Plateau during the Neogene drove intensification of the monsoon system, particularly the East Asian monsoon, by altering atmospheric circulation and enhancing seasonal precipitation contrasts. Evidence from the Chinese Loess Plateau reveals eolian dust accumulation beginning around 22 Ma, with alternating loess-soil sequences indicating strengthened monsoon dynamics that peaked around 15–10.5 Ma, correlating with accelerated Himalayan exhumation rates derived from thermochronometric data. These deposits, spanning up to 29 Ma in initiation, reflect increased aridity in interior Asia and enhanced moisture delivery to eastern margins, linking tectonic elevation to climatic variability.^[54] Neogene ocean circulation models highlight shifts in eastern boundary upwelling systems, notably off Peru and California, which influenced regional productivity patterns. Along the Peruvian margin, the Pisco Formation (10–4.5 Ma) records persistent high primary productivity driven by coastal upwelling, as indicated by diatom-rich sediments and elevated silica fluxes, maintaining nutrient-rich conditions akin to the modern Humboldt Current. In the California Current System, productivity underwent episodic enhancements, including a mid-Pliocene increase (3.5–2.5 Ma) tied to stronger offshore upwelling and subtropical wind intensification, though siliceous microfossil declines between 7 and 5 Ma signal transient reductions in biogenic silica deposition. These changes, reconstructed from Ocean Drilling Program cores, underscore how evolving wind-driven circulation modulated nutrient upwelling and carbon export in these zones.^[55]^[56]

Biodiversity and Evolution

Flora

During the Neogene Period, plant life underwent significant transformations driven by global cooling and increasing aridity, leading to the diversification and redistribution of vegetation across continents. In the early Miocene, extensive forests dominated many regions, featuring broadleaf evergreens in tropical and subtropical zones, while conifers prevailed in higher latitudes of the Northern Hemisphere. These forests supported a rich array of angiosperms, with notable diversification of oaks (Quercus) and beeches (Fagus) in Eurasia, reflecting adaptations to temperate climates and contributing to the development of mixed mesophytic woodlands. Fossil assemblages from this time indicate a humid environment conducive to dense canopy cover, with pollen records showing high diversity in broadleaved taxa.^[57] A pivotal shift occurred with the expansion of grasslands, particularly those dominated by C4 photosynthetic grasses, which became widespread around 7 million years ago (Ma) in response to declining atmospheric CO2 levels, cooler temperatures, and enhanced aridity. This transition replaced C3-dominated woodlands and forests in open habitats, especially in low to mid-latitudes, as C4 grasses proved more efficient in water-scarce conditions. Evidence from stable carbon isotope records in paleosols and tooth enamel across North America, Africa, and Asia documents this rapid ecological change, marking the origin of modern savanna-like biomes. By the late Miocene, these grasslands covered vast areas, influencing soil formation and fire regimes.^[3]^[58] In the Pliocene, vegetation adapted further to a warmer but variably arid climate, with savannas expanding across Africa and the Americas at the expense of tropical rainforests. Pollen records from marine and lacustrine sediments reveal a decline in rainforest taxa, such as those from Bombacaceae and Moraceae, alongside an increase in grass and herbaceous pollen, indicating fragmentation of closed-canopy forests into mosaic landscapes. This shift supported the proliferation of drought-tolerant species and set the stage for Quaternary biome patterns. A key event was the emergence of modern Mediterranean shrublands in regions like the Mediterranean Basin and California, arising from intensified seasonal aridity during the late Miocene to Pliocene, where sclerophyllous shrubs like Quercus coccifera and Arctostaphylos evolved to withstand summer droughts and frequent fires.^[59]^[60]^[61] Fossil evidence underscores these changes, with early Miocene coal swamps in basins like the Most Basin of northern Bohemia preserving lush wetland floras of ferns, equisetums, and angiosperms in low-lying areas. As aridity increased, these transitioned to upland peat deposits by the mid-to-late Neogene, reflecting a shift from swamp-dominated accumulation to mire formation in elevated, better-drained terrains, as seen in lignite seams across Europe and Asia. These deposits provide direct insights into the compositional turnover from hygrophilous to more xerophytic plant communities.^[62]^[63]

Fauna

The Neogene period witnessed significant radiations among terrestrial mammals, particularly herbivores adapted to expanding grasslands. Proboscideans, including early elephants and their relatives, reached their peak diversity during the Miocene, with numerous genera thriving in forested to open habitats before undergoing a marked decline in the Pliocene due to climatic shifts and habitat changes. Similarly, perissodactyls such as rhinoceroses and early horses peaked in the Miocene, coinciding with the spread of C4 grasslands that favored grazing adaptations, but their diversity waned as competition from other ungulates intensified.^[64] In parallel, artiodactyls like bovids (cattle and antelopes) and equids (horses) underwent major diversification in the late Miocene, evolving hypsodont teeth for efficient grass consumption in increasingly arid, open landscapes.^[65] A pivotal event in Neogene faunal dynamics was the Great American Biotic Interchange, initiated around 3 million years ago with the closure of the Isthmus of Panama, forming a land bridge that facilitated bidirectional migrations between North and South America. North American carnivores, including canids, felids, and ursids, dispersed southward, outcompeting and contributing to the decline of South America's native sparassodont marsupials and terror birds.^[66] Conversely, South American xenarthrans such as armadillos, sloths, and glyptodonts migrated northward, diversifying into new niches while some lineages, like ground sloths, reached North America in significant numbers.^[67] This interchange reshaped mammalian communities on both continents, with North American immigrants achieving greater success in colonizing South America due to superior competitive abilities in predatory and grazing roles.^[68] Marine faunas also diversified markedly during the Neogene, with baleen whales (Mysticeti) undergoing a radiation around 15 million years ago in the middle Miocene, as mysticete diversity steadily increased from Oligocene origins to exploit krill-rich upwelling zones.^[69] Concurrently, megatooth sharks of the genus Otodus, including the gigantic O. megalodon, dominated apex predation in coastal and open-ocean ecosystems from the early Miocene until their extinction around 3.6 million years ago, at the boundary between the early and late Pliocene, likely due to cooling oceans and prey scarcity.^[70] Primate evolution in the Neogene featured the proliferation of hominoids, with ape-like forms such as Dryopithecus appearing in Miocene forests of Europe around 12-9 million years ago, alongside similar hominoids in Africa, exhibiting suspensory locomotion and fruit-based diets.^[71] These Eurasian and African hominoids represent key precursors to later hominins, with late Miocene taxa in eastern Africa showing mosaic traits that bridge arboreal apes and bipedal forms emerging near the Miocene-Pliocene boundary.^[72] The late Miocene also saw notable turnover in marine invertebrate communities, driven by global cooling and regional events like the Messinian Salinity Crisis in the Mediterranean, which caused widespread desiccation and led to high extinction rates among benthic species such as foraminifera and mollusks.^[73] This cooling-induced faunal restructuring reduced diversity in warm-water assemblages while promoting cold-adapted taxa, marking a transition toward modern marine ecosystems.^[74]

Controversies and Legacy

Boundary and Classification Debates

The classification of the Neogene has been shaped by historical nomenclature rooted in Charles Lyell's 1833 subdivision of the Tertiary into Eocene, Miocene, and Pliocene based on the percentage of modern molluscan species in fossil assemblages, with the Neogene term itself coined by Moritz Hörnes in 1853 to encompass the Miocene and Pliocene as a unit reflecting post-Eocene faunal modernization.^[9] This Lyellian framework introduced confusion by treating the Tertiary as a broad interval extending toward the Recent, overlapping with what later became the Quaternary, and leading to inconsistent usage where "Neogene" was sometimes expanded informally to include Quaternary deposits due to perceived faunal continuity.^[9] Modern standardization by the International Commission on Stratigraphy (ICS) has resolved much of this by elevating Paleogene and Neogene to formal periods within the Cenozoic Era, abandoning "Tertiary" as an informal sub-era, though traditional stage names like Burdigalian persist alongside updated ones, perpetuating minor nomenclatural debates in regional stratigraphy.^[9] The transition from the Oligocene (Paleogene) to the Miocene (Neogene) at approximately 23.03 Ma has sparked discussions on whether to conceptualize it as part of a broader "Paleogene-Neogene" continuum rather than a discrete boundary, given the gradual nature of faunal and floral shifts without a major extinction event. Proponents of a merged supraprocess argue that the boundary's definition at the Global Boundary Stratotype Section and Point (GSSP) at the Lemme-Carrosio Section, Alessandria Province, Italy—defined by the base of a distinct claystone unit correlated with the base of magnetic polarity Chron C6Cn.2r—overemphasizes a minor climatic cooling and ignores diachronous marine and terrestrial changes across continents.^[12] This gradualism is evident in mammalian faunas, where archaic groups like uintatheres wane slowly into modern lineages without abrupt turnover, challenging the Paleogene-Neogene divide as an artificial construct in evolutionary terms. Debates over the Miocene-Pliocene boundary, formally placed at 5.333 Ma, center on its 1995 recalibration from an earlier estimate of about 5.1 Ma, achieved through astronomical tuning of Mediterranean sapropels that refined the age but highlighted discrepancies in global correlation.^[75] The GSSP at Eraclea Minoa, Sicily, defined by the base of the Trubi Formation, with auxiliary markers including the first occurrence of the ostracod Amamonia toscoi, has faced criticism for coinciding with a paraconformity representing a brief hiatus of roughly 20,000 years, which some argue obscures the boundary's biostratigraphic signal and complicates integration with non-Mediterranean sections lacking similar cyclic sediments.^[76] Despite ratification in 2000, ongoing disputes emphasize the need for auxiliary markers like the coiling change in Neogloboquadrina pachyderma to resolve regional variations in boundary placement.^[76] The most prominent controversy involves the Quaternary's relationship to the Neogene, where pre-2009 ICS usage included the Quaternary (from the Pliocene-Pleistocene boundary to the present) within the Neogene, reflecting continuous post-Miocene faunal evolution toward modern assemblages.^[77] The 2009 decision to establish the Quaternary as a separate system beginning at 2.58 Ma—ratified via the GSSP at Monte San Nicola, Sicily, tied to a marine isotope stage—truncated the Neogene accordingly, but paleontologists advocating reintegration cite faunal continuity in mammalian and molluscan records, such as the unbroken progression of proboscideans and equids, as evidence that the 2.58 Ma boundary artificially severs a unified "Neogene-Quaternary" interval.^[77] Proposals for an "inclusive compromise" suggest flexible hierarchies allowing overlapping usage in biostratigraphy while maintaining strict chronostratigraphic separation, though this remains unresolved amid concerns over nomenclatural stability.^[77]

Research Gaps and Modern Implications

Despite significant progress in Neogene paleontology and paleoclimatology, several key research gaps persist. High-resolution climate proxies for the early Pliocene remain limited, particularly in regions like the South China Sea Basin, where geochemical indicators such as clay mineralogy and rare earth elements provide insights into paleoweathering but lack the temporal precision needed for detailed reconstructions.^[78] Similarly, multiproxy approaches to equatorial Pacific sea surface temperatures highlight spatial gaps in early Pliocene data, necessitating statistical methods to interpolate missing records from sparse sediment cores.^[79] Microbial and insect fossils from this period are notably understudied, with plant-insect interactions sparsely documented despite recent findings of rare skeletonization damage on Pliocene leaves in India, underscoring the need for broader surveys of these biotic traces.^[80] Furthermore, integrating molecular clock estimates with stratigraphic records reveals ongoing discrepancies in dating mammal divergences, as relaxed clock models often yield ages that conflict with fossil-based chronologies, complicating evolutionary timelines for Neogene lineages.^[81] Post-2020 advances have begun addressing these challenges through innovative methodologies. Genomic studies of placental mammal evolution, leveraging hundreds of loci across non-coding regions, have refined divergence timelines for Neogene taxa, revealing previously undetected hybridization events that influenced lineage formation.^[82] In parallel, satellite-derived digital elevation models and high-resolution imagery have enhanced paleotopography reconstructions, enabling more accurate simulations of Neogene landscape dynamics and their climatic interactions, particularly in tectonically active regions like the northern Tibetan Plateau.^[83] The Neogene holds substantial modern relevance as an analog for anthropogenic climate change. Pliocene sea levels, estimated at 17.5 ± 6.4 meters above present during the early epoch, serve as a benchmark for future projections under elevated CO2, with mid-Pliocene warmth (2–3°C above pre-industrial) mirroring potential 21st-century scenarios and highlighting ice sheet vulnerabilities.^[84] Biodiversity patterns from the late Miocene, including functional diversity losses in African megafauna due to environmental shifts, parallel contemporary declines, where trait-environment mismatches accelerated ecosystem disruptions.^[85] Resource-wise, Neogene sedimentary basins like the Southern North Sea continue to underpin energy security, with ongoing exploration revealing untapped hydrocarbon potential amid maturing fields and implications for sustainable extraction strategies.^[86] Looking ahead, future research directions emphasize refined chronostratigraphy and modeling. Astrochronology offers promise for achieving finer resolutions of Neogene stages, as demonstrated by revised orbital calibrations for Miocene sections that align biostratigraphic events with Milankovitch cycles, paving the way for global standardization.^[87] Climate models incorporating Neogene CO2 feedbacks, such as those from carbonate weathering and vegetation shifts, will be crucial for capturing late Miocene transitions and predicting amplified warming under rising greenhouse gases.^[88]

References

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Neogene Period—23.0 to 2.58 MYA - National Park Service
Apr 27, 2023 · The Neogene Period is the middle period of the three periods of the Cenozoic Era. Like the other periods of the Cenozoic, it is geologically short.
[2]
Neogene Period | Natural History Museum
The Neogene encompasses two epochs, beginning with the Miocene (23.03-5.33 Mya) and followed by the Pliocene (5.33-2.58 Mya).
[3]
Cenozoic Expansion of Grasslands and Climatic Cooling
Grassland expansion in the Cenozoic, with its unique soils, may have contributed to long-term global climatic cooling and drying.
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Neogene Ice Age in the North Atlantic Region: Climatic Changes ...
Long-term climatic trends in the North Atlantic region during Neogene time probably resulted primarily from tectonic events.
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The late Cenozoic was a time of global cooling, increased aridity, and expansion of grasslands. In the last two decades numerous records of ...
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Cenozoic Era | GeoKansas - The University of Kansas
Neogene animals and plants include rhinoceros, tapirs, horses, kangaroo rats, salamanders, elm trees, hackberry trees, and grasses. Trace fossils of animal ...Missing: climate fauna flora
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Chronostratigraphic Chart - International Commission on Stratigraphy
This page contains the latest version of the International Chronostratigraphic Chart (v2024-12) which visually presents the time periods and hierarchy of ...
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The Neogene: Origin, adoption, evolution, and controversy
Some stratigraphers have recently insisted that for historical reasons, the Neogene (Miocene + Pliocene) should be extended to the present.
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[PDF] Untitled - Subcommission on Neogene Stratigraphy
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[PDF] The Global Boundary Stratotype Section and Point for the base of ...
The GSSP was approved by the International Commission on Stratigraphy (ICS) and ratified by the International Union of Geological. Sciences (IUGS) in 1991.
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[PDF] INTERNATIONAL CHRONOSTRATIGRAPHIC CHART
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GSSP Table - Geologic TimeScale Foundation
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[PDF] 9. neogene diatom biostratigraphy of the middle latitude western
Diatoms are abundant and well preserved throughout the section. Seven diatom zones were recognized with- out zonal breaks in Hole 580 (Table 4, back pocket) ...
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[PDF] Plate tectonic regulation of global marine animal diversity
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[PDF] Cenozoic tectonic evolution of the Himalayan orogen as constrained ...
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[PDF] Neogene marine isotopic evolution and the erosion of Lesser ...
tectonic shift in the evolution of the Himalayan orogeny, which resulted from a southward advance in the position of the active thrust belt. Given the ...
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The folds and faults kinematic association in Zagros - Nature
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Mar 15, 2022 · A high-resolution model of the motion between Nazca and South American plates is presented. The work shows rapid changes that help explaining ...
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[PDF] History of the development of the East African Rift System
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[PDF] 4. Neogene Tectonic Evolution of the Celebes-Sulu Basins
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[PDF] The Yellowstone Hotspot, Greater Yellowstone Ecosystem, and ...
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High-resolution reconstructions and GPS estimates of India–Eurasia ...
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Atmospheric carbon dioxide variations across the middle Miocene ...
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Chapter 9: Ocean, Cryosphere and Sea Level Change
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Sep 11, 2020 · Deep-sea benthic foraminifera preserve an essential record of Earth's past climate in their oxygen- and carbon-isotope compositions.
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Limited Mediterranean sea-level drop during the Messinian salinity ...
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Late Neogene evolution of the Peruvian margin and its ecosystems
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[PDF] Neogene evolution of the California Current System - ODP Legacy
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Tree diversity in the Miocene forests of Western Eurasia
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[PDF] Early Miocene freshwater and swamp ecosystems of the Most Basin ...
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The Early Pliocene extinction of the mega-toothed shark Otodus ...
Feb 13, 2019 · The youngest reliable records of Otodus megalodon are early Pliocene, suggesting an extinction at the early-late Pliocene boundary (∼3.6 Ma).
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Fossil apes and human evolution - Science
May 7, 2021 · Humans diverged from apes (chimpanzees, specifically) toward the end of the Miocene ~9.3 million to 6.5 million years ago.
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A new ape from Türkiye and the radiation of late Miocene hominines
Aug 23, 2023 · Fossil apes from the eastern Mediterranean are central to the debate on African ape and human (hominine) origins.
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The marine biodiversity impact of the Late Miocene Mediterranean ...
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The Central Paratethys Sea—rise and demise of a Miocene ... - Nature
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(PDF) The age of the Miocene-Pliocene boundary - ResearchGate
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https://www.science.org/doi/10.1126/science.abb4363
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Neogene and Quaternary coexisting in the geological time scale
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Evaluating the Neogene paleoclimatic record of northwestern Luzon ...
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[PDF] Multiproxy Reduced‐Dimension Reconstruction of Pliocene ...
In this study, we apply a statistical method to a compilation of nine Pliocene SST records across the equatorial Pacific to fill in the spatial gaps in the ...
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New discovery of rare insect damage in the Pliocene of India ...
We document evidence of a new type of insect skeletonization on Abroma augustum (L.) L. f. (Malvaceae) leaf remains from the latest Neogene (Pliocene) ...
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A genomic timescale for placental mammal evolution - Science
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[PDF] On the reconstruction of palaeo-ice sheets: Recent advances ... - HAL
Jun 24, 2021 · Improved spatial resolution of satellite imagery and Digital Elevation Models, and better access to high- resolution data in readily ...
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A Revised Estimate of Early Pliocene Global Mean Sea Level Using ...
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Disruption of trait-environment relationships in African megafauna ...
Jul 18, 2023 · We observe that losses in the large herbivores' functional diversity commenced following the environmental changes of the late Miocene. Prior to ...
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New insights on subsurface energy resources in the Southern North ...
The Southern North Sea Basin area, stretching from the UK to the Netherlands, has a rich hydrocarbon exploration and production history.
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Revised astrochronology for the Lower to Middle Miocene of IODP ...
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Carbonate weathering, CO2 redistribution, and Neogene CCD and ...
Nov 1, 2022 · This study instead focuses on parameters that most directly reflect carbon fluxes to address broad scale changes in the Earth system since the ...