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Proboscidea

Proboscidea is an order of eutherian mammals within the clade Afrotheria, encompassing the three extant species of elephants—Loxodonta africana (African savanna elephant), Loxodonta cyclotis (African forest elephant), and Elephas maximus (Asian elephant)—along with over 160 extinct relatives including mammoths, mastodons, and gomphotheres.^[1]^[2] Members of this order are distinguished by their elongated, muscular proboscis (trunk) used for feeding, manipulation, and respiration; elongated upper incisors forming prominent tusks; massive crania; and pillar-like limbs supporting enormous body masses often exceeding several tons.^[3]^[2] The evolutionary history of Proboscidea traces back approximately 60 million years to the late Paleocene or early Eocene in Africa, where the earliest known forms, such as Phosphatherium and Numidotherium, emerged as small, pig-sized herbivores within the broader Afrotheria group, which also includes hyraxes, sirenians, and aardvarks.^[4]^[5] Over the Cenozoic era, proboscideans underwent significant diversification, radiating into at least 10 families, 42 genera, and around 175 species and subspecies, adapting to diverse habitats across Africa, Eurasia, and the Americas through migrations facilitated by land bridges.^[6]^[3] Key evolutionary trends included increasing body size (gigantism), development of complex grinding molars for processing abrasive vegetation, and specialized trunks for browsing and grazing, with many lineages achieving ecological dominance as megaherbivores.^[7] Proboscideans reached their peak diversity during the Miocene and Pliocene epochs, with forms like gomphotheres and deinotheres spreading globally and influencing ecosystems through their foraging and seed dispersal roles.^[3] However, most lineages went extinct during the late Pleistocene, likely due to climate change, habitat loss, and human hunting pressures, leaving only the Elephantidae family today.^[8] Modern elephants, the sole survivors, exhibit remarkable intelligence, complex social structures, and long gestations of up to 22 months, underscoring their unique adaptations.^[2] Recent phylogenetic analyses, incorporating total evidence and ancient DNA, have clarified interfamily relationships, supporting a basal position for early African forms and confirming Elephantidae's monophyly with mammoths and mastodons as derived groups.^[8]

Taxonomy and Definition

Etymology and Scope

The order Proboscidea was established by German zoologist Johann Karl Wilhelm Illiger in 1811 to encompass living and extinct elephants (Elephantidae) and their relatives, such as the American mastodon.^[9] The name derives from the New Latin Proboscidea, rooted in the Greek proboškís (προβοσκίς), meaning "elephant's trunk" or "one with a trunk," highlighting the defining elongated nasal appendage central to the group's identity.^[9] This etymology underscores the order's focus on mammals characterized by a prehensile proboscis adapted for feeding, manipulation, and social behaviors. Proboscidea belongs to the mammalian superorder Afrotheria, a clade of primarily African-origin mammals that also includes orders like Hyracoidea (hyraxes) and shares a common ancestry with Sirenia (sirenians).^[10] The scope of Proboscidea extends to all known trunk-bearing herbivorous mammals, from primitive Paleogene forms to the three extant elephant species—African bush elephant (Loxodonta africana), African forest elephant (L. cyclotis), and Asian elephant (Elephas maximus)—representing a lineage that originated in Africa and dispersed globally.^[10] Approximately 175 species and subspecies have been recognized across 10 families, with the vast majority extinct, illustrating the order's historical diversity and adaptive radiation as large-bodied herbivores.^[6] Key diagnostic traits of proboscideans include the elongated, muscular proboscis (trunk) formed by fusion and extension of the nose and upper lip; pillar-like, columnar limbs supporting immense body mass; and high-crowned (hypsodont) molars with complex folding for grinding abrasive vegetation.^[11]^[12] These features evolved to facilitate a herbivorous lifestyle in varied terrestrial environments. Early taxonomic classifications underwent significant revisions; for instance, in 1834, Henri Marie Ducrotay de Blainville grouped proboscideans with sirenians under "gravigrades," a cohort later refined as Tethytheria, before molecular and morphological evidence separated them into distinct orders within Paenungulata.^[13]

Phylogenetic Relationships

Proboscidea belongs to the superorder Afrotheria, a monophyletic clade of placental mammals that also encompasses paenungulates such as hyraxes (Hyracoidea) and sirenians (Sirenia), along with other African-endemic groups like elephant shrews, tenrecs, golden moles, aardvarks, and sengis. This placement emerged from molecular phylogenetic analyses in the late 1990s, which revealed unexpected affinities among morphologically disparate African mammals through comparisons of nuclear and mitochondrial DNA sequences.^[14] Subsequent genomic studies have robustly confirmed Afrotheria's monophyly, with high bootstrap support across large-scale phylogenomic datasets, highlighting shared retrotransposon insertions and protein sequence signatures as additional molecular evidence.^[15]^[16] Morphological synapomorphies supporting Afrotheria are limited due to extensive adaptive divergence, but key features include the testicond condition (intra-abdominal testes without descent into a scrotum), an elevated number of thoracolumbar vertebrae (typically 20 or more), and certain dental patterns such as the pseudohypocone on upper molars, which reflects early stages of lophodonty.00223-8)^[17]^[18] Within Afrotheria, Proboscidea forms part of the subclade Paenungulata alongside Hyracoidea and Sirenia, where morphological traits like a continuous navicular facet on the astragalus in the ankle joint provide additional support for this grouping, though these are more pronounced in paenungulates.^[19] Debates persist regarding the exact branching order within Paenungulata, with early molecular studies yielding conflicting topologies—such as Proboscidea sister to Sirenia or to Hyracoidea—but 2020s phylogenomic analyses using whole-genome data reveal an almost perfect polytomy, with gene trees supporting various resolutions and only 8-10% of genes providing statistically significant signal to reject the hypothesis of unresolved branching.^[20]^[21] This configuration aligns with some fossil-calibrated trees, emphasizing rapid diversification. Fossil evidence, including early Paleocene afrotherian-like remains from North Africa, corroborates molecular estimates of an initial afrotherian divergence around 80 million years ago in the Late Cretaceous, prior to the end-Cretaceous extinction, when Africa was isolated as a landmass favoring endemic radiations.^[22]^[23]

Major Taxonomic Groups

The order Proboscidea comprises 10 families, encompassing 175 species and subspecies classified across 42 genera, with only 3 species extant today.^[24] This classification, as outlined in seminal taxonomic work, reflects a hierarchical structure that includes both early diverging and advanced lineages, with Proboscidea nested within the Afrotherian clade of placental mammals.^[24] Recent paleontological revisions in the 2020s have refined genus-level distinctions, such as the separation of Palaeoloxodon from Elephas based on cranial morphology and molecular data from ancient DNA.^[25] The basal family Moeritheriidae, known from the Eocene epoch, represents one of the earliest proboscidean radiations and includes the genus Moeritherium as its type, a small-bodied form that anchors the family's nomenclatural history.^[24] Deinotheriidae is distinguished by genera like Deinotherium, featuring unique tusks curving downward from the lower jaw, with type specimens from Miocene and Pliocene deposits establishing its monotypic status within the family.^[24] Gomphotheriidae encompasses diverse forms from the Miocene, including genera such as Gomphotherium and Anancus, with ongoing taxonomic adjustments elevating certain subfamilies to reflect phylogenetic branching.^[24] Mammutidae, commonly referred to as mastodons, includes key genera like Mammut and Zygolophodon, with the family's nomenclature tracing back to early 20th-century descriptions based on North American fossils.^[24] The family Elephantidae, established by John Edward Gray in 1821 through analysis of extant elephant morphology, houses modern elephants and their close extinct relatives, such as mammoths; it comprises two extant genera—Loxodonta (African elephants, including L. africana and L. cyclotis) and Elephas (Asian elephant, E. maximus)—along with extinct ones like Mammuthus (woolly mammoth) and Palaeoloxodon.^[26]^[24] The remaining families—Numidotheriidae, Barytheriidae, Palaeomastodontidae, Phiomiidae, and Stegodontidae—include genera such as Numidotherium, Barytherium, Palaeomastodon, Phiomia, and Stegodon, respectively, contributing to the order's total of over 170 extinct species.^[24]

Evolutionary History

Origins in the Paleocene

The earliest known proboscideans emerged in Africa during the late Paleocene, approximately 60 million years ago, evolving from endemic ungulate-like mammals within the superorder Afrotheria.^[27] These proto-proboscideans represent the basal radiation of the order in a period shortly after the Cretaceous-Paleogene extinction, with fossils indicating small-bodied forms adapted to forested or wetland environments.^[28] The order Proboscidea is nested within Afrotheria based on both molecular and morphological evidence, underscoring its African continental origins.^[29] A key early genus is Phosphatherium escuilliei, a small, semi-aquatic proboscidean dating to 59–56 million years ago, discovered in the Ouled Abdoun phosphate basin of Morocco.^[30] Standing less than one meter at the shoulder and weighing around 10–15 kg, Phosphatherium featured bunodont teeth suited for browsing soft vegetation and enlarged, procumbent upper incisors that served as precursors to tusks, alongside evidence of a short, fleshy proboscis-like structure indicated by the retracted position of the nasal opening. This genus exemplifies the primitive morphology of early proboscideans, bridging them to later forms through shared dental and cranial traits.^[31] During the Eocene, proboscideans underwent an initial radiation, notably with the Moeritheriidae family around 37–35 million years ago, known from abundant fossils in the Fayum Depression of Egypt. These semi-aquatic, hippopotamus-like forms reached up to 200 kg in body mass and inhabited marshy, riverine habitats, as evidenced by stable carbon and oxygen isotope analyses of their tooth enamel showing a diet of aquatic plants and an amphibious lifestyle.^[32] Moeritheriids displayed further elongation of the incisors as proto-tusks and adaptations for wading, such as shortened limbs, marking key evolutionary steps toward more specialized proboscidean traits.^[33] By the late Eocene, early proboscidean dispersals had reached Eurasia, broadening their distribution beyond Africa as suggested by tentative dental fossils from southern Asia.^[11]

Diversification During the Miocene

The Miocene epoch (23–5 million years ago) marked the peak of proboscidean diversity, with the order undergoing a major adaptive radiation that resulted in numerous genera and species across multiple continents.^[34] This expansion began with migrations out of Africa into Eurasia around 22 million years ago, facilitated by climatic changes and land connections, leading to widespread distribution.^[35] By the middle to late Miocene, proboscideans had reached North America via the Bering land bridge, further diversifying into new ecological niches.^[35] Overall, proboscidean taxonomic richness reached its zenith during this period, with estimates of around 175 species and subspecies recognized across the order's history, many originating or peaking in the Miocene.^[36] Key families that diversified during the Miocene included Gomphotheriidae, Deinotheriidae, and the earliest members of Elephantidae. Gomphotheriidae, often featuring shovel-like tusks adapted for browsing or grazing vegetation, underwent rapid speciation and became dominant in Eurasia and North America, with genera like Gomphotherium exemplifying this radiation.^[8] Deinotheriidae, characterized by unique downward-curving lower tusks used for stripping bark from trees, originated in the Oligocene but achieved greater abundance and geographic spread in the Miocene across Africa and Eurasia.^[37] Early Elephantidae, ancestors to modern elephants, emerged in the late Miocene, initially in Africa, with forms showing preliminary adaptations toward more open habitats.^[38] Adaptive innovations during the Miocene drove this diversification, particularly shifts in diet and body size. Many proboscideans transitioned from browsing on soft forest vegetation to grazing on tougher grasses, accompanied by the evolution of high-crowned (hypsodont) molars for processing abrasive plants, as seen in middle Miocene Gomphotherium fossils from Central Asia containing grass phytoliths.^[39] Body sizes increased significantly, with species like Gomphotherium reaching shoulder heights of about 3 meters and weights of 4–5 tons, enabling exploitation of diverse habitats from woodlands to emerging grasslands.^[40] These changes coincided with global cooling and the spread of C4 grasslands, promoting niche partitioning among sympatric species.^[41] Important fossil sites from the Miocene include the Bugti Hills in Pakistan, which preserve early Miocene proboscideans documenting initial migrations from Africa to Asia, and the Samburu Hills in northern Kenya, yielding late Miocene assemblages with diverse gomphotheres and deinotheres.^[42]^[43] Recent discoveries in the 2020s, such as refined ecomorphological analyses from East African sites, have clarified migration routes and dietary transitions, showing how biogeographic expansion beyond Africa fueled functional diversity.^[44]

Quaternary Extinctions and Survivors

The Quaternary period, spanning from approximately 2.6 million years ago to the present, marked a profound decline in proboscidean diversity, with the vast majority of genera—estimated at over 90%—becoming extinct, leaving only the modern elephants as survivors.^[45] This mass extinction primarily affected iconic groups such as mammoths (Mammuthus spp.), American mastodons (Mammut americanum), and various gomphotheres (e.g., Cuvieronius and Stegomastodon), which had thrived across Eurasia, North America, and South America during the Pleistocene.^[46] Radiocarbon dating of fossil remains indicates that the peak of these extinctions occurred between 12,000 and 10,000 years ago, coinciding with the transition from the Pleistocene to the Holocene epoch.^[47] Pollen records from sediment cores further corroborate this timeline, revealing rapid shifts in vegetation from open grasslands to closed forests, which altered habitats critical for these large herbivores.^[48] Multiple interacting factors contributed to this late-Quaternary collapse, including abrupt climate change at the end of the Last Glacial Maximum, intensified human hunting pressures, and consequent habitat fragmentation. The termination of Ice Age conditions around 11,700 years ago led to warmer temperatures and altered precipitation patterns, reducing the extent of steppe-tundra ecosystems that supported proboscidean populations.^[49] Human activities, particularly by Paleoindian groups, played a significant role, as evidenced by Clovis culture sites in North America where fluted spear points have been found embedded in mammoth and mastodon bones, indicating targeted hunting of proboscideans around 13,000–11,000 years ago.^[50] Habitat loss exacerbated these pressures, with expanding human populations and megafaunal overhunting leading to ecosystem destabilization, as supported by overlapping radiocarbon chronologies of human arrivals and proboscidean disappearances across continents.^[51] While debates persist on the relative weights of climatic versus anthropogenic drivers, integrated evidence from isotopic analysis and archaeological contexts points to a synergistic effect driving the extinctions.^[52] Amid this widespread die-off, only two genera within the family Elephantidae persisted: Loxodonta (African elephants) in sub-Saharan Africa and Elephas (Asian elephants) in South and Southeast Asia, retreating to isolated refugia where fragmented forests and savannas provided relative sanctuary from hunting and climatic extremes.^[53] Recent genomic studies from the 2020s, analyzing whole-genome sequences from wild populations, reveal that these survivors endured severe population bottlenecks during the late Pleistocene, resulting in critically low genetic diversity—such as only two mitochondrial haplotypes in some Asian elephant groups—and heightened vulnerability to inbreeding depression.01177-1) Island populations occasionally delayed local extinctions; for instance, dwarfed woolly mammoths (Mammuthus primigenius) on Wrangel Island in the Arctic Ocean survived in isolation until approximately 4,000 years ago, as determined by radiocarbon dating of over 100 bone and ivory samples spanning 7,000–4,000 years before present.^[54] These insular endemics, adapted to a resource-limited environment post-land bridge submersion around 12,000 years ago, represent one of the latest known holdouts of non-elephantid proboscideans.^[55]

Anatomy and Morphology

Overall Body Plan

Proboscideans exhibit a massive, herbivorous body build characterized by pillar-like limbs that provide robust support for their enormous weight, which in extinct forms could reach up to 14 tons.^[56] Their torso is barrel-shaped to accommodate a large digestive system for processing fibrous vegetation, while the head is positioned low on the shoulders to maintain balance under the pull of heavy cranial structures.^[3] This graviportal architecture, with straight, columnar legs resembling pillars, evolved to distribute the animal's mass efficiently during movement and standing.^[57] The skin of proboscideans is notably thick, measuring up to 4 cm in extant elephants, offering protection against environmental hazards and aiding in thermoregulation.^[58] In modern elephants, the skin is sparsely haired, but extinct species like the woolly mammoth possessed a denser coat for insulation in colder climates.^[59] Ear size varies for thermoregulatory purposes, with African elephants featuring large, flap-like ears that facilitate heat dissipation through increased surface area and blood vessel exposure.^[60] Locomotion in proboscideans is adapted to their size via a pillar-legged gait, enabling a top speed of approximately 25 km/h in bursts despite their bulk.^[61] Skeletal adaptations include fused carpals and tarsals in the wrists and ankles, which enhance stability and reduce flexibility to better withstand compressive forces during weight-bearing.^[57] Sexual dimorphism is pronounced in proboscideans, with males generally larger and displaying more robust skeletal features compared to females, as evidenced by comparisons between fossil remains and living elephants.^[62] This size disparity, often exceeding 30% in body mass, likely relates to male-male competition for mates.^[56]

Trunk, Tusks, and Dentition

The trunk, or proboscis, of proboscideans is a multifunctional appendage formed by the fusion of the nose and upper lip, functioning as a muscular hydrostat capable of precise movements without skeletal support.^[63] Composed of approximately 90,000 muscle fascicles arranged in longitudinal, radial, and transverse orientations, the trunk enables elongation, shortening, bending, and constriction through antagonistic muscle contractions.^[64] In extant elephants, it reaches lengths of up to 2 meters, with the distal tip exhibiting exceptional dexterity due to miniaturized fascicles as small as 10 cubic micrometers in volume, allowing fingertip-like grasping—African elephants possess two such protrusions, while Asian elephants have one.^[65] This structure facilitates object manipulation, such as plucking vegetation or wielding tools, as well as drinking by siphoning water or dust into the mouth via suction generated by nostril dilation.^[66] Additionally, the trunk serves in communication through tactile interactions and trunk-to-trunk contact for social bonding, and it integrates sensory functions, including touch via specialized mechanoreceptors at the tip.^[67] The olfactory capabilities of the trunk surpass those of dogs, supported by around 2,000 functional olfactory receptor genes—more than twice the approximately 800 in canines—enabling detection of scents over several kilometers for locating food, water, or kin.^[68] Tusks in proboscideans are elongated upper incisors that grow continuously throughout life, primarily composed of dentin (commonly termed ivory) overlaid by a thin layer of cementum and an initial enamel cap that wears away early.^[69] In extinct species like woolly mammoths, tusks could exceed 3 meters in length, curving outward to aid in foraging by uprooting vegetation, defense against predators, and intraspecific displays for dominance or mating.^[70] Modern elephants retain similar functions, using tusks to dig for minerals or strip bark, though intense poaching pressure has driven evolutionary shifts toward tusklessness in some populations, particularly females in regions like Gorongosa National Park, where genetic mutations on the X chromosome linked to tusk development have increased in frequency due to selective survival advantages.^[71] Proboscidean dentition features a unique horizontal replacement system, with molars migrating forward from the back of the jaw as anterior teeth wear down from abrasive foraging, allowing up to six sets per lifetime in elephants.^[72] These molars are lophodont, with transverse ridges adapted for grinding tough plant material, evolving from the bunodont (cusped) teeth of basal Paleocene proboscideans like Phosphatherium to the highly hypsodont (high-crowned) forms in later grazers such as mammoths, enhancing durability against silica-rich grasses.^[3] This serial replacement and morphological progression reflect adaptations to increasingly abrasive diets over proboscidean evolution.^[73]

Size Variations and Dwarfism

Proboscideans exhibit a remarkable range in body size across their evolutionary history, from diminutive basal forms to colossal later species. Early proboscideans, such as Phosphatherium and Moeritherium from the Eocene, were small, pig-sized herbivores weighing approximately 10 to 200 kg and standing less than 1 meter at the shoulder.^[11]^[28] In contrast, the largest known proboscideans, including Palaeoloxodon namadicus from the Pleistocene of Asia, achieved shoulder heights of up to 4.3 meters and body masses estimated at 10 to 14 tons, representing the peak of terrestrial mammalian gigantism.^[74]^[75] Modern elephants, the sole surviving proboscideans, are considerably smaller; African bush elephants (Loxodonta africana) typically weigh 2 to 6 tons with shoulder heights of 3 to 4 meters, while Asian elephants (Elephas maximus) average 2 to 5 tons and 2.5 to 3 meters.^[76]^[77] This size variation follows allometric scaling principles, where body mass increases cubically with linear dimensions like shoulder height, influencing locomotion, thermoregulation, and resource requirements.^[56] Growth in proboscideans is characterized by rapid juvenile development supported by nutrient-rich maternal milk, enabling calves to achieve substantial size early in life. Elephant milk contains high levels of protein, typically 2.5% to 4.7% in early lactation, along with elevated fat content, which fuels accelerated somatic growth and prepares offspring for weaning around 2 to 4 years of age.^[78]^[79] Sexual maturity is reached at 10 to 15 years, with females often maturing earlier (around 10 to 12 years in African elephants) than males (12 to 15 years), marking the transition to reproductive adulthood after a prolonged period of dependency.^[80]^[81] Fossil evidence from tusk cross-sections reveals incremental growth rings, analogous to tree rings, that record annual or seasonal deposition rates, providing insights into individual health, diet, and age at death in extinct species like mammoths and mastodons.^[82]^[83] Insular dwarfism represents a striking adaptation in proboscideans isolated on islands, where body size reductions occur as part of the broader "island rule" evolutionary pattern, driven by limited resources and reduced predation pressure rather than climatic factors like Bergmann's rule. On Mediterranean islands such as Sicily and Malta, Palaeoloxodon falconeri evolved to a shoulder height of about 1 meter and a body mass of 200 to 300 kg, roughly 1% the size of its mainland ancestor Palaeoloxodon antiquus.^[84]^[85] Similarly, on California's Channel Islands, the pygmy mammoth Mammuthus exilis diminished to approximately 1.7 meters at the shoulder and 700 to 800 kg, a fraction of the 6- to 10-ton Columbian mammoth from which it descended, with some estimates suggesting even smaller individuals approaching 200 kg.^[86] These reductions likely enhanced survival in resource-scarce environments by lowering metabolic demands and accelerating maturation rates.^[87] Recent genomic analyses in the 2020s, including comparisons of ancient DNA from insular and mainland proboscideans, have begun to identify potential genetic mechanisms underlying size reduction, such as alterations in growth hormone pathways, though full causal links remain under investigation.^[88]

Ecology and Biology

Habitats and Distribution

Proboscideans achieved a cosmopolitan distribution during the Miocene through the Quaternary periods, with fossil evidence spanning diverse environments from Arctic tundras to tropical forests across all continents except Australia and Antarctica.^[2] Early forms originated in Africa around 55 million years ago and dispersed to Eurasia via land bridges approximately 18-19 million years ago, later reaching North America around 5-6 million years ago through Beringia and even extending to South America.^[8] Iconic cold-adapted species like the woolly mammoth (Mammuthus primigenius) inhabited northern high latitudes, including Siberia, Alaska, and parts of Canada, thriving in steppe-tundra ecosystems up to the Arctic Circle during the Pleistocene.^[89] Today, the three extant proboscidean species occupy fragmented ranges in Africa and Asia. African elephants (Loxodonta africana and L. cyclotis) are distributed across sub-Saharan Africa in savanna woodlands, grasslands, and tropical forests, with a total estimated range of approximately 5.9 million km², though much of this is under pressure from human activity. Asian elephants (Elephas maximus) inhabit dry and wet forests, grasslands, and shrublands across 13 countries from India through Southeast Asia to Indonesia, covering about 500,000 km²—roughly 5% of their historical extent.^[90] Proboscideans exhibit strong habitat preferences tied to resource availability, particularly water, which they require in substantial volumes due to their large body size and thermoregulatory needs. Both extant species drink 100-200 liters of water daily, often accessing permanent sources like rivers or waterholes to prevent dehydration, and they avoid arid interiors without reliable moisture.^[91] Asian elephants demonstrate notable elevational flexibility, typically ranging from sea level to 3,000 meters but occasionally ascending higher into Himalayan foothills to evade heat or follow seasonal vegetation.^[90] Climate variability profoundly influences proboscidean distribution through seasonal migration patterns synchronized with wet and dry cycles. In savanna ecosystems, African elephants shift ranges to exploit flush of grasses and water during wet seasons, contracting to riverine areas in dry periods, with movements covering hundreds of kilometers in response to rainfall.^[92] Similarly, Asian elephants in monsoon-driven habitats migrate altitudinally or laterally to track forage and water, though ongoing fragmentation has reduced these patterns. Recent tracking data from the 2020s indicate a roughly 50% contraction in suitable range since 1900, driven by habitat loss and isolation into smaller patches, limiting adaptive responses to climate shifts.^[93]

Diet, Foraging, and Physiology

Proboscideans are strictly herbivorous, consuming a diverse array of plant material to meet their high energetic demands. Extant species, such as the African savanna elephant (Loxodonta africana), ingest approximately 100–300 kg of vegetation daily, depending on body size, availability, and season.^[94]^[95] Dietary preferences vary by habitat and taxon: forest-dwelling proboscideans like the African forest elephant (Loxodonta cyclotis) primarily browse on twigs, leaves, bark, and fruits in wooded environments, while savanna inhabitants favor grasses and sedges as grazers.^[96] This dichotomy is reflected in dental adaptations, with molars in grazing lineages evolving high-crowned (hypsodont) structures and complex enamel folding to withstand abrasion from silica phytoliths in grasses, a trait that emerged prominently in the Miocene as open habitats expanded.^[97] Foraging strategies in proboscideans rely heavily on the multifunctional trunk, which enables precise manipulation for plucking leaves, stripping bark, or uprooting grasses without using teeth, allowing selective feeding on nutrient-rich parts of plants.^[98] Individuals typically travel 10–50 km per day in search of food patches, covering extensive ranges to compensate for the low nutritional quality of their diet.^[99] Digestion occurs via hindgut fermentation in the enlarged cecum and colon, where a diverse gut microbiome—dominated by bacteria such as Fibrobacter and Ruminococcus—breaks down cellulose and other fibrous components into volatile fatty acids for energy extraction.^[100] This microbial symbiosis is essential, as proboscideans lack the foregut rumination of smaller herbivores, achieving moderate efficiency (around 40–50% for cellulose) through prolonged retention times of up to 60 hours.^[101] Physiological adaptations support survival on this low-energy diet and in arid or variable climates. Proboscideans exhibit a basal metabolic rate approximately 50% lower than expected for their body mass based on interspecific scaling laws, reducing daily energy expenditure and enabling sustained foraging with minimal fat reserves.^[102] Water conservation is facilitated by temporary storage in the trunk (up to 10 liters) and pharyngeal pouches near the throat, which hold 3–5 liters for short-term hydration between drinking bouts every 2–3 days.^[103] Thermoregulation involves large, vascularized ears that dissipate heat through convection and evaporation, potentially lowering core temperature by 3–5°C, supplemented by mud baths that provide evaporative cooling and UV protection.^[104] Reproduction is adapted to long lifespans, with gestation lasting about 22 months—the longest among mammals—and twinning occurring in less than 1% of births due to limited uterine capacity and maternal resources.^[105] Evolutionary transitions in diet are evident from fossil records, particularly in the Miocene when climatic cooling and aridification promoted C4 grasslands. Early proboscideans relied on C3 browse, but lineages like deinotheres and early elephantids shifted toward C4 grasses, as indicated by increasing δ¹³C values in tooth enamel and microwear patterns showing coarser scratches from abrasive silica.^[41] These changes, dated to around 7–5 million years ago in Africa, drove dental innovations such as ever-growing molars, enhancing processing of tougher vegetation and facilitating diversification into open biomes.^[96]^[106] Proboscideans, particularly elephants, exhibit complex social structures characterized by matriarchal family units. These herds typically consist of 8 to 100 related females and their offspring, led by the oldest female, known as the matriarch, who guides the group in decision-making for movement, foraging routes, and responses to threats.^[107] Male proboscideans, in contrast, leave their natal herds at maturity and live solitarily or in loose, temporary associations with other males, often forming bachelor groups without the stable bonds seen in female kin groups. Allomothering is a common practice within these herds, where non-maternal females, such as aunts or older sisters, provide care to calves, including protection, grooming, and teaching, which enhances calf survival rates especially for young or inexperienced mothers.^[108] Communication among proboscideans is multimodal, facilitating coordination over varying distances and contexts. They produce infrasonic rumbles with fundamental frequencies of 14-24 Hz, which can travel up to several kilometers in open habitats, allowing herds to maintain contact or signal alarms.^[109]^[110] Close-range interactions involve tactile signals like trunk touches to mouths, genitals, or bodies for greeting and reassurance, while chemical cues from temporal gland secretions convey information on reproductive status, identity, and emotional states such as aggression during musth.^[111]^[112] Reproductive strategies in proboscideans are polygynous, with males competing for access to females through displays and combat, often heightened during musth—a periodic state of elevated testosterone that induces aggression and attraction via temporal gland secretions and urine dribbling.^[113] Females reach sexual maturity around 10-12 years, with gestation lasting 18-22 months, the longest among mammals, followed by calving intervals of 4-5 years to allow for extended maternal investment.^[114]^[115] Proboscideans have lifespans of 60-70 years in the wild, during which learned behaviors—such as migration routes and social norms—are transmitted matrilineally from matriarchs to offspring and kin, preserving cultural knowledge across generations.^[116]^[117] Evidence from fossil bone beds and trackways suggests that extinct proboscideans like mammoths maintained similar matriarchal herd structures, with assemblages often dominated by female and juvenile remains indicative of family groups traveling together.^[118]^[119] In extant species, observations in the 2020s have documented mourning-like rituals, where elephants investigate, touch, and linger over deceased kin or even unfamiliar carcasses, appearing subdued and covering bodies with vegetation, reflecting deep social bonds.^[120]^[121]

Conservation and Human Impact

Extant Species Status

The extant species of Proboscidea are the African savanna elephant (Loxodonta africana), the African forest elephant (L. cyclotis), and the Asian elephant (Elephas maximus). The African savanna elephant is classified as Endangered on the IUCN Red List, with a population estimated at approximately 352,000 individuals as of the 2016 Great Elephant Census, which covered 93% of the savanna range and remains a key reference for recent assessments.^[122] Recent total African elephant estimates indicate around 415,000-540,000 individuals as of 2024, with savanna elephants comprising the majority.^[123] The African forest elephant is recognized as a distinct species and listed as Critically Endangered, with current estimates placing its population at fewer than 100,000 individuals, concentrated mainly in Central African forests like Gabon, where recent surveys indicate around 95,000.^[124] The Asian elephant is also Endangered, with a wild population ranging from 40,000 to 50,000 individuals across its fragmented range in Asia.^[125] Genetic health across these species is compromised by habitat fragmentation and small population sizes, resulting in reduced diversity and risks of inbreeding depression, which manifests as decreased fitness, higher juvenile mortality, and lower reproductive success. Studies in the 2020s utilizing single nucleotide polymorphisms (SNPs) from whole-genome sequencing have revealed that Asian elephants display higher levels of inbreeding and lower heterozygosity compared to African elephants, attributable to their smaller overall numbers and more isolated subpopulations.^[126] For instance, fragmented Asian populations show elevated homozygosity in key genomic regions, exacerbating vulnerability to environmental stressors.^[127] In African elephants, while savanna populations maintain relatively higher diversity due to larger group sizes, forest elephants exhibit notable declines in genetic variability in isolated Central African groups.^[128] Subspecies variation further highlights status disparities. The African forest elephant (L. cyclotis) represents a distinct lineage with specialized adaptations to dense forests, but its Critically Endangered status underscores severe population isolation. Among Asian elephant subspecies, the Sri Lankan elephant (E. m. maximus) is the largest, with adult males averaging up to 5,500 kg and noted for its darker pigmentation and robust build; its population stands at approximately 11,000 individuals based on 2024 national census estimates finalized in 2025, comprising about 22% of the total Asian elephant count.^[129]^[130] Accurate census and health monitoring rely on advanced non-invasive techniques. GPS collars enable real-time tracking of movement patterns and home ranges in both African and Asian populations, providing data on group dynamics and habitat use.^[131] Complementarily, dung DNA analysis allows for genetic identification of individuals without disturbance, facilitating population estimates, kinship analysis, and detection of inbreeding in remote areas like African forests.^[132] These methods have improved census precision, revealing previously undercounted groups and supporting targeted genetic management.^[133]

Threats and Extinction Risks

Poaching for ivory remains a primary threat to African elephants (Loxodonta africana), with an estimated 100,000 individuals killed across the continent between 2010 and 2012 due to surging illegal trade demands.^[134] This selective pressure has driven rapid evolutionary changes, including an increase in tuskless females to approximately 30% in certain populations, such as in Mozambique's Gorongosa National Park, where poachers disproportionately target tusked individuals.^[135] Similar poaching incidents affect Asian elephants (Elephas maximus), though at lower intensities, exacerbating vulnerability through targeted removal of large-tusked males. Habitat loss from deforestation and agricultural expansion has fragmented over 60% of suitable elephant ranges in Asia since 1700, confining populations to isolated patches that limit gene flow and increase isolation.^[93] In Africa, comparable pressures have reduced forest elephant distributions by about 30% in recent decades, further compounded by human-elephant conflicts.^[136] These conflicts are acute in India, where crop-raiding elephants result in approximately 600 human deaths and 150 elephant deaths annually, based on 2020-2024 data, often from retaliatory killings or accidental encounters.^[137] Climate change intensifies these risks by prolonging droughts that diminish water and forage availability, leading to malnutrition and heightened mortality among elephants.^[138] Models project that rising temperatures could cause up to 40% habitat loss for African elephants in regions like Zimbabwe by 2050, forcing greater overlap with human areas and amplifying conflict.^[139] Diseases such as anthrax pose additional dangers, with outbreaks killing over 100 elephants in Botswana in 2019 amid drought-stressed conditions that facilitate spore ingestion.^[140] Competition with livestock for grazing resources further strains elephant foraging, particularly in fragmented landscapes where pastoralism encroaches on habitats.^[141] In India, anthrax incidents in wild elephants highlight the role of livestock interfaces in disease transmission.^[142] The interplay of these threats—poaching, habitat fragmentation, climate-induced scarcity, and disease—cumulatively elevates extinction risks for both elephant species, potentially leading to functional extinction where surviving populations lose ecological roles. Low genetic diversity, arising from isolation, compounds this vulnerability by reducing adaptive capacity.^[143]

Conservation Efforts

Conservation efforts for proboscideans, particularly elephants, encompass a range of international legal frameworks, protected area designations, monitoring programs, and innovative initiatives aimed at safeguarding populations and habitats. The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) listed all elephant populations in Appendix I in 1989, effectively banning international commercial trade in ivory to curb overexploitation.^[144] National parks play a crucial role in habitat protection; for instance, Amboseli National Park in Kenya serves as a key conservation area for African elephants, supporting long-term monitoring and protection of approximately 1,870 individuals as of early 2025 through collaborative efforts between researchers and local communities.^[145]^[146] Similarly, Kaziranga National Park in India provides essential safeguards for Asian elephants within its diverse ecosystem, contributing to broader wildlife protection as a UNESCO World Heritage Site with a century-long history of conservation management.^[147] Key initiatives include the CITES Monitoring the Illegal Killing of Elephants (MIKE) program, established in 1997, which operates a site-based system across Africa and Asia to track trends in illegal killings, build management capacity, and inform policy decisions through data collection from protected areas.^[148] In India, rewilding projects focus on securing elephant corridors to facilitate movement and genetic connectivity; the national Elephant Corridors of India report identifies 150 such pathways, with efforts like the Wildlife Trust of India's Right of Passage project rehabilitating conflict-affected areas and restoring connectivity spanning over 100 kilometers in critical landscapes.^[149]^[150] Notable successes demonstrate the impact of community-driven approaches and technology. In Namibia, community conservancies have facilitated a significant rebound in African elephant numbers, growing from approximately 7,600 in 1995 to 25,664 by 2023 through sustainable resource management and benefit-sharing models that empower local stakeholders.^[151]^[152] Anti-poaching technologies, such as drones equipped with AI for real-time detection, have enhanced patrol efficiency in African reserves; programs like Air Shepherd have conducted over 4,000 missions to deter threats and monitor elephant movements in regions like Zimbabwe and South Africa.^[153] As of 2025, the IUCN Species Survival Commission released updated African Elephant Status Reports (December 2024 for forest elephants, June 2025 for savanna elephants), confirming Endangered and Critically Endangered statuses respectively while highlighting stable but vulnerable populations and the need for enhanced transboundary efforts.^[154] Looking to the future, transboundary collaborations address habitat fragmentation by linking ecosystems across borders. The Kavango-Zambezi Transfrontier Conservation Area (KAZA TFCA), spanning about 520,000 km² across Angola, Botswana, Namibia, Zambia, and Zimbabwe, integrates 36 protected areas to support the world's largest contiguous elephant population through joint management and anti-poaching strategies.^[155] In the 2020s, emphasis has shifted toward human-wildlife coexistence, with compensation schemes reimbursing communities for losses incurred from elephant interactions, as outlined in global guidelines promoting sustainable livelihoods alongside conservation.^[156]

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Despite a common misconception, elephants cannot suck water directly from their stomachs. Instead, it is the pharyngeal pouch that provides them with this ...
[106]
How elephants keep their cool - NU Sci Magazine
Jan 14, 2020 · Their ears can help lower an elephant's body temperature by 5 degrees Fahrenheit. The African elephant's ability to stay cool in the hot sub- ...
[107]
Rare elephant twins born in Samburu
Jan 19, 2022 · The African elephant has the largest gestation period of any living mammal – at approximately 22 months and gives birth roughly every four ...
[108]
(PDF) A New Tooth Wear–Based Dietary Analysis Method for ...
Apr 23, 2015 · C3 plants in diet, and most of the C4 plants are grasses, which should be reﬂected in the mesowear signal. SUPPLEMENTAL DATA—Supplemental ...
[109]
Early evidence for complex social structure in Proboscidea from a ...
Feb 22, 2012 · No less than 14 different trackways at Mleisa 1 are attributable to Proboscidea on the basis of the round shape and large size of the prints, ...Missing: diversity | Show results with:diversity
[110]
Allomothering among African elephants - ScienceDirect.com
Allomothers tended to be family members but were not always siblings. Siblings maintained close proximity to calves, while calf defence also involved less ...Missing: aunt | Show results with:aunt
[111]
Infrasonic calls of the Asian elephant (Elephas maximus)
Most of the calls ranged in frequency from 14 to 24 Hz, with durations of 10–15 s (Fig. 1). With the nearest elephant 5 m from the microphone, sound pressure ...Missing: rumbles km<|control11|><|separator|>
[112]
Establishing the fundamentals for an elephant early warning and ...
Sep 4, 2015 · Elephants make extensive use of powerful infrasonic calls (rumbles) that travel distances of up to several kilometers. This makes elephants well ...
[113]
Multimodal communication and audience directedness in the ...
May 9, 2024 · When they meet, wild male elephants may occasionally rumble and often direct their trunks to their conspecifics' mouth, temporal glands, or ...
[114]
How elephants communicate - ElephantVoices
In this section we look at how elephants use the different pathways of communication and the actual mechanics of communicating. In the fully searchable database ...
[115]
Male African Elephant (Loxodonta africana) Behavioral Responses ...
May 1, 2022 · Driven by reproductive motives, male African elephants (Loxodonta africana) in musth often expand their home ranges to locate estrous females.Missing: lifespan | Show results with:lifespan
[116]
Elephant gestation period longer than any living mammal - BBC Earth
African elephants are pregnant for an average of 22 months, whilst for Asian elephants it's 18 to 22 months.Missing: interval lifespan 60-70
[117]
Nearby grandmother enhances calf survival and reproduction in ...
Jun 10, 2016 · Elephant pregnancy lasts around 22 months and birth intervals <1.8 and >12.4 years (95% quartile of birth interval length) were therefore ...
[118]
longevity and senescence in wild female African elephants - NIH
Jan 19, 2016 · Elephants, humans and whales share a lifespan of 70–100+ years, making them rare among mammals. Maximum lifespan has been estimated at 74 years ...
[119]
On the Loss of a Matriarch - Save the Elephants
Jul 14, 2015 · Foley's research indicates that when a matriarch dies the family loses something incredibly important: knowledge.
[120]
Columbian Mammoth (U.S. National Park Service)
Oct 12, 2021 · Like modern elephants, Columbian mammoths most likely lived in multigenerational, matriarchal (female led) herds, with a dominate mature female ...
[121]
Rare Mammoth Tracks Reveal an Intimate Portrait of Herd Life
Feb 26, 2018 · As he explains, mammoth herds, like modern elephants, are thought to have moved in matriarchal groups, led by an older female.
[122]
Researchers Study Elephants' Unique Interactions with Their Dead
Feb 8, 2020 · The most common behaviors observed were approaching the dead, touching and examining the carcass. Elephants also appeared to use their advanced ...
[123]
insights into dead calf carrying and other thanatological responses ...
May 18, 2022 · Using videos uploaded on YouTube, we document and construct a tentative repertoire of thanatological responses (death-related behaviours) in Asian elephants ( ...
[124]
Continent-wide survey reveals massive decline in African savannah ...
Aug 31, 2016 · Results ; South Africa, 17,433, 0 ; Tanzania, 42,871, 3,102 ; Uganda, 4,864, 1,031 ...
[125]
African Forest Elephant - Global Conservation
Jan 12, 2025 · African forest elephants are critically endangered, with only 400 remaining in Cameroon. They are smaller than savanna elephants, with ...
[126]
Asian elephants: intelligent, sociable, but endangered - WWF-UK
Jan 24, 2024 · Today, there are fewer than 50,000 Asian elephants left in the wild. They are also listed as endangered species on the IUCN Red List. Asian ...Asian Elephants: Intelligent... · Why Asian Elephants Are So... · Adopt An Elephant
[127]
Genomic resources for Asian (Elephas maximus) and African ...
In extreme cases, decreased genetic diversity may lead to inbreeding depression (Vidya et al. ... We extracted SNPs that were polymorphic within Asian elephants ...
[128]
Article Divergence and serial colonization shape genetic variation ...
Oct 21, 2024 · To better understand whether elephant populations such as SSG are endangered by imminent inbreeding depression, we compared the number and ...
[129]
Genomics Reveals Distinct Evolutionary Lineages in Asian Elephants
Aug 18, 2025 · The genome of the Bornean elephant exhibited signatures of severe bottlenecks as recently as 8 and 38 generations ago, further supporting ...
[130]
Genetic features of Sri Lankan elephant, Elephas maximus maximus ...
Jun 13, 2023 · Elephas maximus maximus Linnaeus, the Sri Lankan subspecies is the largest and the darkest among Asian elephants. Patches of depigmented areas ...<|separator|>
[131]
Sri Lanka completes first elephant census since 2011 amid uncertainty
Sep 12, 2024 · According to the count, 55% of the population were adult elephants, with 1,107 calves. These results, particularly the sex ratio and number of ...
[132]
Elephant Evaluation: Health, Welfare, Population Dynamics, and ...
Aug 22, 2025 · Methods for Population Monitoring and Census Techniques ... Elephant Collars equipped with GPS technology are a cornerstone of modern monitoring.
[133]
A New Way to Count African Forest Elephants: DNA From Dung
Jul 29, 2022 · We used a non-invasive technique in which we collected DNA from elephant dung and used that highly individualized genetic material to accurately identify ...
[134]
Genotyping dung advances conservation of endangered forest ...
Aug 9, 2024 · The scientific team set out to collect elephant dung while tracking 10 males and 10 females across 20 herds. As herds defecate synchronously, ...
[135]
100,000 African elephants killed in three years | University of Oxford
Aug 19, 2014 · An estimated 100,000 elephants were killed for their ivory between 2010 and 2012 according to new research by a team including Oxford ...Missing: 2010-2020 | Show results with:2010-2020
[136]
Ivory poaching and the rapid evolution of tusklessness in African ...
Oct 21, 2021 · Intensive poaching in Africa has been associated with an increase in the frequency of tuskless elephants, exclusively (or nearly so) among ...
[137]
African forest elephants | World Wildlife Fund
Mar 3, 2021 · Their populations declined by 62% between 2002 and 2011, and during that period, the species also lost 30% of its geographical range. As this ...
[138]
Solving India's deadly conflict between humans and elephants - CNN
Jun 20, 2021 · Around 500 people and 100 elephants die every year in India, as the country's growing population encroaches on wildlife habitats.Missing: yearly | Show results with:yearly
[139]
Deepening drought and the threat to iconic African elephants | WWF
Apr 9, 2025 · One study found that 205 elephants died as a result of the drought in Kenya in the nine months between February and October 2022.Missing: malnutrition 30% 2050
[140]
5 Ways Climate Change Is Affecting Elephants and 1 Surprising ...
Apr 22, 2023 · Scientists now expect African elephants in Zimbabwe to lose 40% of their habitat by 2050 due to rising temperatures.
[141]
than 100 elephants die in Botswana in suspected anthrax outbreak
Oct 23, 2019 · "Due to the severe drought, elephants end up ingesting soil while grazing and get exposed to the anthrax bacteria spore," it said.
[142]
Competition and compensation among cattle, zebras, and elephants ...
Elephants eat both grass and forbs, and may compete differentially with cattle (which eat both) and zebras (which eat only grass).
[143]
Anthrax deaths in elephants: environment ministry releases SOP
Jan 21, 2020 · In October 2019, more than 100 elephants died in Botswana due to a suspected anthrax outbreak. In India, sporadic deaths of wild elephants due ...
[144]
Illegal killing for ivory drives global decline in African elephants | PNAS
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[145]
Ivory sales get the go-ahead - CITES
CITES banned the international commercial ivory trade in 1989. Then, in 1997, recognizing that some southern African elephant populations were healthy and ...
[146]
Amboseli trust for elephants: ATE
The Amboseli Trust for Elephants (ATE) helps ensure the long-term conservation of Africa’s elephants, monitoring over 3500 elephants. Wild elephants in ...Contact us · Amboseli · Amboseli & us · Elephant history
[147]
Kaziranga National Park - UNESCO World Heritage Centre
The park has a long history of protection for over a century, reflected in the dramatic recovery of the rhino. The park has been declared as a Tiger Reserve in ...Gallery · Videos · Maps · Documents<|separator|>
[148]
Monitoring the Illegal Killing of Elephants (MIKE) - CITES
MIKE Programme is a site-based system designed to monitor trends in the illegal killing of elephants, build management capacity and provide information.
[149]
[PDF] Elephant Corridors of India 2023
This report is an outcome of the collective efforts of Project Elephant of the MoEFCC and the State Forest. Departments with technical support from the Wildlife ...
[150]
RIGHT OF PASSAGE: NATIONAL ELEPHANT CORRIDORS ...
Right of passage aims to protect elephant corridors, while simultaneously rehabilitating people affected by conflict in corridor areas.
[151]
Facts and Figures - Community Conservation Namibia
Namibia's elephant population grew from around 7,600 to around 23,600 between 1995 and 2016 according to aerial survey data. Lions have increased in range and ...Missing: African | Show results with:African
[152]
Air Shepherd: Leading Rhinos and Elephants to Safety - RESET.ORG
Air Shepherd flies drones to stop poaching. To date, they've piloted over 4,000 missions to stop rhino and elephant poachers. In their own words, ...
[153]
Kavango Zambezi - Peace Parks Foundation
The Kavango Zambezi (KAZA) transboundary landscape spans an area of approximately 520 000 km² and includes 36 proclaimed protected areas across Angola, ...
[154]
[PDF] Human-Elephant Conflict And Coexistence - The World Bank
Human-wildlife conflict compensation schemes are implemented by government agen- cies or NGOs working in protected or conserved areas. The scheme reimburses ...Missing: 2020s | Show results with:2020s