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Notoptera

Notoptera is a small order of wingless insects within the superorder Polyneoptera, consisting of two extant suborders: Grylloblattodea (ice crawlers or rock crawlers) and Mantophasmatodea (gladiators or heelwalkers), both characterized by their relict status, limited species diversity, and specialized habitats.^[1]^[2] These insects are hemimetabolous, undergoing incomplete metamorphosis with egg, nymph, and adult stages, and feature mandibulate mouthparts, filiform antennae, and tarsi typically divided into five segments.^[2]^[3] With approximately 60 extant species in total, Notoptera represents one of the least diverse insect orders, highlighting their ancient lineage and vulnerability to environmental changes.^[1]^[3] The suborder Grylloblattodea, containing the single family Grylloblattidae with about 40 species across 6 genera, includes insects that are pale, cylindrical, and range from 10 to 40 mm in length, often with reduced eyes and long, multi-segmented cerci.^[1] These cold-adapted, nocturnal omnivores scavenge on detritus, arthropod remains, and plant material, thriving in alpine and subalpine environments such as caves, under stones, in moss, or near perpetual snow in the Holarctic region, including western North America, Siberia, China, Korea, and Japan.^[2] They are highly sensitive to temperature, remaining active below freezing but perishing above 10°C, and exhibit slow development with generations spanning up to 7 years.^[2] In contrast, Mantophasmatodea, comprising three families with approximately 20 species across 11 genera, features carnivorous insects with robust, thorn-studded forelegs for capturing prey, short one-segmented cerci, and bodies measuring 10-30 mm, adapted for climbing with tarsal pads.^[4]^[3]^[5] These nocturnal predators hunt small arthropods like spiders and insects, hiding in rock crevices, grass clumps, or arid shrublands during the day, and are restricted to semi-arid to arid regions in southern Africa, particularly Namibia (e.g., Brandberg and Erongo Mountains) and South Africa.^[3]^[5] Discovered as a living order only in 2002 after initial identification from fossils and museum specimens, Mantophasmatodea includes extinct species from Baltic amber dating back 40-45 million years.^[3]^[5] Notoptera's evolutionary history traces to the Late Carboniferous, with fossil evidence of winged ancestors in the mid-Cretaceous, including the recent discovery of Zygogrylloblatta longipalpa, indicating an ecological shift from arboreal to terrestrial lifestyles, resulting in the apterous (wingless) forms seen today.^[1]^[6] This bipolar distribution—Grylloblattodea in northern cold zones and Mantophasmatodea in southern arid areas—underscores their relictual nature and monophyletic origin, supported by shared synapomorphies such as the mentum-submentum angle in the head.^[1] Despite their obscurity and lack of economic impact, these insects provide key insights into polyneopteran evolution and the effects of climate on insect diversification.^[2]^[3]

Taxonomy

Classification

Notoptera is a monophyletic clade within the infraclass Neoptera, specifically the cohort Polyneoptera, and is characterized by hemimetabolous development in which immature stages resemble adults but lack functional wings. Phylogenetic analyses based on extensive transcriptomic data place Notoptera as the sister group to the remaining Polyneoptera, with a close relationship to Plecoptera (stoneflies) and Orthoptera (grasshoppers and crickets).^[7] This positioning underscores its basal role among polyneopterans, supported by both molecular and morphological evidence that confirms the clade's integrity despite the relictual nature of its extant members.^[6] The name Notoptera was originally coined by Crampton in 1915 as an ordinal name for the then-enigmatic Grylloblattidae, though it fell into disuse for decades.^[8] The group's taxonomic status was revived and elevated to order level following the discovery of the sister group Mantophasmatodea in southern Africa in 2002, which provided the first living representatives beyond the relict Grylloblattidae. In their molecular phylogenetic study, Terry and Whiting (2005) proposed Xenonomia as an alternative name for the combined clade, recognizing its monophyly based on shared genetic markers and morphological convergences, though Notoptera remains the preferred senior synonym in current classifications.^[9] Classification of Notoptera relies on several shared derived characters (synapomorphies), including a distinct angle exceeding 60° between the submentum and mentum of the labium, posteriorly oriented labial palpi, and a flat, lobe-like hypopharynx with its suspensorium positioned far ventrad of the mouth opening. Additional diagnostic traits encompass the loss of specific head muscles, such as the musculus tentorioparaglossalis, and a unique neural connection between the antennal ampulla and supraesophageal ganglion featuring clustered nuclei. These features, derived from detailed head morphology studies, distinguish Notoptera from other polyneopterans and support its monophyly, with further reinforcement from fossil evidence of reduced ovipositor structures and conserved wing venation patterns in extinct relatives.^[10] The living families are Grylloblattidae and Mantophasmatidae.^[7]

Included families and species

The order Notoptera is divided into two extant suborders: Grylloblattodea, comprising the single family Grylloblattidae, and Mantophasmatodea, comprising the family Mantophasmatidae.^[11] The family Grylloblattidae, commonly known as rock crawlers or ice crawlers, includes approximately 40 extant species distributed across six genera and is primarily found in Holarctic regions, including northwestern North America, eastern Siberia, northern China, Korea, and Japan.^[11] These wingless insects are adapted to cold, montane environments, with species diversity concentrated in western North America, where 13 species of the genus Grylloblatta have been described, alongside up to 16 additional undescribed taxa identified from various high-elevation sites such as the Sierra Nevada, Olympic Mountains, and Trinity Mountains.^[12] The family Mantophasmatidae, known as gladiators or heel-walkers, encompasses about 21 extant species in 14 genera, all endemic to southern Africa, particularly Namibia, South Africa, and Tanzania.^[13] In some classifications, this family is subdivided into three families—Austrophasmatidae, Mantophasmatidae, and Tanzaniophasmatidae—reflecting phylogenetic and geographic distinctions among the genera, though taxonomic arrangements vary with recent discoveries emphasizing their carnivorous, wingless nature.^[4] Overall, Notoptera supports approximately 60 described extant species worldwide across these two families, though the total diversity is likely higher due to numerous undescribed forms, particularly within Grylloblattidae.^[11]^[13] Fossil records reveal a richer past diversity, with extinct families assigned to early notopteran lineages such as those within the orders Eoblattida and Reculida, dating from the Permian to Triassic periods and characterized by winged forms that contrast with the apterous modern representatives. These groups, including families like Atactophlebiidae and Geinitziidae, indicate that ancestral Notoptera occupied more varied ecological niches before the loss of flight in extant lineages.^[14]

Morphology

External anatomy

Notoptera exhibit a distinctive elongate body plan, characterized by a cylindrical abdomen and a relatively large head capsule. The head features prominent compound eyes and long, multisegmented antennae; in Grylloblattidae, the antennae are filiform, while in Mantophasmatidae, they are filiform but densely setose with specialized sensilla for sensory functions. The prothorax is enlarged and shield-like, providing protective cover over the head and anterior thorax, particularly pronounced in Grylloblattidae.^[15]^[16] The mouthparts of Notoptera are of the chewing (mandibulate) type, well-suited for predation and scavenging, with generalized orthopteroid structure featuring toothed mandibles, five-segmented maxillary palps, and three-segmented labial palps.^[16]^[15] The legs are cursorial, adapted for running on surfaces, with strong femora suitable for grasping prey, though lacking true raptorial modifications seen in mantises. In Mantophasmatidae, a unique "heel-walking" gait is enabled by the elevation of the distalmost (fifth) tarsomere, which remains raised off the substrate, while the proximal four tarsomeres bear adhesive euplantulae with tenent setae for traction. All tarsi are five-segmented across both families.^[15]^[17] The abdomen consists of 10 visible segments, with cerci present as short, one- to multi-segmented appendages on the terminal segment. Females possess a reduced ovipositor, short and inconspicuous in Grylloblattidae and somewhat more projecting but still subdued compared to other polyneopterans in Mantophasmatidae. All extant Notoptera are wingless, though some fossil relatives show vestigial wing pads. Body lengths range from 10 to 40 mm, with sexual dimorphism evident in antennal length (longer in males of some species) and abdominal shape (broader apically in males, mid-abdominally in females), alongside overall size differences where females are typically larger.^[15]

Sensory and locomotor adaptations

Notoptera exhibit specialized sensory adaptations suited to their often nocturnal and low-light habitats, with visual structures particularly reduced. Ocelli are poorly developed or absent in many species, particularly within Grylloblattidae, where they are entirely lacking, reflecting an emphasis on non-visual senses in dim environments.^[18] Compound eyes are small or reduced across the order, further limiting reliance on vision.^[19] Chemoreceptive capabilities are prominent on the antennae, which bear diverse sensilla for detecting chemical cues from prey or scavenged organic matter. In Mantophasmatodea, the antennal flagellum features sensilla coeloconica, basiconica, and trichodea, primarily serving olfactory and gustatory functions to sense environmental volatiles and contact chemicals.^[20] Similarly, in Grylloblattidae, antennal sensilla and sensitive hairs on palpi enable detection of dead arthropods and plant matter in cold, moist microhabitats.^[21] Tactile setae distributed on the legs and cerci facilitate navigation through dark, cluttered substrates like leaf litter or under rocks, providing mechanosensory feedback for obstacle avoidance and substrate texture assessment.^[22]^[19] Locomotor adaptations emphasize stability and efficiency in rugged or cold terrains, supported by robust thoracic structures. The thorax houses strong musculature dedicated to leg movement, enabling running, climbing, and foraging across uneven surfaces despite the loss of flight capabilities.^[23] In Mantophasmatidae, adhesive tarsal euplantulae—proximal pads covered in elongated tenent setae with single-pointed or spatulate tips—enhance grip on rocky outcrops, complemented by reduced proximal claws that interlock with surface irregularities for secure adhesion during vertical climbing.^[17] Conversely, Grylloblattidae display a slow, deliberate gait optimized for energy conservation in subzero temperatures near glacial margins, with slender legs and minimal attachment modifications suited to deliberate crawling under snow or moss.^[21] Respiration in Notoptera follows the typical insect tracheal system, with air entering through paired spiracles on the thorax and abdomen to deliver oxygen directly to tissues via branching tracheae.^[24] No specialized gills are present, even in species inhabiting wet, icy edges, underscoring their terrestrial lifestyle despite occasional exposure to high humidity.^[21] The nervous system is centralized, comprising a ventral nerve cord with fused segmental ganglia that coordinate sensory inputs and motor outputs, particularly adapted for low-light and cold conditions. In Grylloblattidae, the ventral cord and cercal nerves feature extensive glial sheathing and large mitochondria, enhancing neural stability at near-freezing temperatures to support nocturnal activity.^[22]^[25] This configuration integrates tactile and chemosensory data from appendages to guide precise, low-energy locomotion in obscured environments.^[24]

Distribution and habitats

Geographic range

The order Notoptera displays a markedly disjunct global distribution, characterized by the absence of overlap between the family Grylloblattidae (suborder Grylloblattodea) and the three families of suborder Mantophasmatodea (Austrophasmatidae, Mantophasmatidae, and Tanzaniophasmatidae), resulting in a fragmented range spanning roughly 60°N to 5°S.^[26]^[27]^[4] Grylloblattidae are confined to the Holarctic realm, with populations restricted to cold, mountainous regions in the northern hemisphere and no extension into southern latitudes. In North America, the family is represented by approximately 15-20 species in the genus Grylloblatta, primarily inhabiting high-elevation sites in the Rocky Mountains, Cascade Range, and Sierra Nevada from southern British Columbia through Washington, Oregon, California, and into Montana.^[28] In Asia, around 20 species across five genera (Galloisiana, Grylloblattina, Grylloblattella, Namkungia, and Grylloprimevala) occur in cool temperate forests and montane areas of Japan, the Korean Peninsula, China (including the Changbai Mountains), and the Russian Far East extending to western Siberia's Altai and Sayan Mountains, as of 2025.^[28]^[27]^[29] The overall latitudinal range for Grylloblattidae extends from 33°N to 60°N, underscoring their adaptation to northern cryophilic environments. With approximately 35-40 species across 6 genera total as of 2025, the family shows recent additions from ongoing surveys.^[30] The suborder Mantophasmatodea, by contrast, is exclusively Afrotropical, with species in three families distributed across southern and eastern Africa. The Mantophasmatidae (3-5 species in 3-4 genera) are limited to Namibia, clustering in arid and semi-arid landscapes, including inselbergs and massifs such as the Brandberg Massif and Gamsberg. The Austrophasmatidae (8-10 species in 5 genera) occur in South Africa, particularly in the Succulent Karoo and Namaqualand regions. The monotypic Tanzaniophasmatidae (1 species, Tanzaniophasma burchelli) is known from eastern Africa in Tanzania. The suborder has approximately 20-25 described extant species as of 2025, all endemic to these localized, rocky terrains.^[26]^[4] Notoptera exhibit high levels of endemism overall, with numerous species micro-endemic to specific mountain ranges or inselbergs, contributing to their vulnerability and the order's relictual biogeographic pattern.^[26]^[27]

Environmental preferences

Notoptera display distinct environmental preferences shaped by the contrasting ecologies of their two suborders, underscoring their relictual status in specialized niches. Grylloblattodea (family Grylloblattidae) are strictly cold-adapted insects, thriving in microclimates with optimal temperatures of 0–10°C and exhibiting high mortality rates above 10°C, as these conditions align with their physiological limits for survival and activity.^[2]^[31]^[27] In contrast, Mantophasmatodea favor warmer, thermophilic environments, remaining active during daytime hours in hot periods (often exceeding 20°C) but shifting to nocturnal behaviors to mitigate excessive heat exposure, particularly in arid landscapes.^[26] High moisture levels are essential across both suborders, though manifested differently due to habitat disparities. Grylloblattodea demand near-saturation humidity (above 70–100%) to prevent desiccation, occupying perpetually damp sites such as glacial talus slopes, ice-adjacent caves, and stream banks where snowmelt or groundwater maintains wet conditions year-round.^[31]^[28] Mantophasmatodea, while tolerant of semi-arid to dry regimes, rely on episodic high humidity—such as morning fog or post-rainfall moisture—for critical life stages like oviposition, which occurs preferentially in cooler, damper mornings within their otherwise xeric habitats.^[26]^[32] Both suborders preferentially inhabit concealed microhabitats that buffer against abiotic stresses and biotic pressures, including leaf litter, mossy crevices, and rock fissures, while strictly avoiding exposed open areas vulnerable to predation and rapid drying. Grylloblattodea cluster in cool, shaded refugia like subalpine talus or cave interiors near perennial ice, where stable moisture and low light prevail.^[33] Mantophasmatodea seek shelter under stones, within grass tussocks (e.g., Poaceae or Restionaceae), or amid dwarf shrubs in rocky shrublands and savannas, leveraging these sites for ambush predation and evasion of diurnal heat.^[26]^[32] These narrow preferences render Notoptera highly susceptible to environmental perturbations, particularly climate warming, which is eroding cold, wet refugia for Grylloblattodea through glacier retreat and rising temperatures that exceed their thermal tolerances.^[28]^[27] Habitat fragmentation further exacerbates risks by isolating populations in diminishing suitable patches, while for Mantophasmatodea, additional pressures like vegetation burn-off in fire-prone savannas compound the loss of microhabitat structure.^[26]

Biology

Reproduction and life cycle

Notoptera reproduce sexually through indirect sperm transfer, in which males produce and deliver spermatophores to females during copulation. In the suborder Mantophasmatodea, copulation is prolonged, lasting an average of 14.7 hours (ranging from 11 to 21 hours in observed species such as Tyrannophasma gladiator and Mantophasma spp.), with males mounting females in a "false male-above" position using cerci for clasping; females may continue foraging during this time.^[26] In some species, copulation can extend up to three days, potentially involving the formation of a spermatophore from accessory gland secretions for sperm nourishment and protection.^[34] For Grylloblattodea, mating behaviors are less documented but involve the male chasing and seizing the female under stones, leading to spermatophore transfer; copulation duration is typically 30 minutes to 4 hours.^[19] Oviposition in Notoptera is delayed following mating, occurring days to months later, and females deposit eggs in protected, moist microhabitats to enhance survival. Mantophasmatodean females lay eggs in foam pods that harden into sandy cocoons, typically 0.5–2 cm deep in soil; each pod contains 20–30 eggs (e.g., 26–30 in T. gladiator, 20–24 in Mantophasma spp.), with individuals producing up to four pods for a total of 50–100 eggs, often during morning hours under cool, humid conditions.^[26] Grylloblattodean females use their elongate ovipositor to place coal-black, ellipsoidal eggs (approximately 1.6 mm long) singly or a few at a time (e.g., 5–6 eggs per day) into rotten wood, under stones, in moss, or soil crevices, with total fecundity varying by species up to 60–150 eggs per female, with deposition 10–50 days post-copulation.^[19]^[33] Egg incubation lasts 6–12 months across both suborders, hatching during favorable seasons like rainy periods in Mantophasmatodea or cooler months in Grylloblattodea.^[26]^[21] The life cycle of Notoptera is hemimetabolous, featuring egg and nymph stages that resemble miniature adults, with no pupal phase. Nymphs undergo 5–8 instars, depending on the suborder; Mantophasmatodea typically complete 5 instars in 55 days to 4.5 months under laboratory conditions (21–23°C), reaching sexual maturity within 1 year as part of an annual, univoltine cycle.^[26] Grylloblattodea require longer development, with 8 instars over 5–7 years to maturity, also univoltine but adapted to cold environments where generations overlap.^[33]^[21] Sexual maturity occurs at the final instar in both groups, with adults living 1–2 years post-maturation. No parental care is provided, leaving eggs and nymphs exposed to fungal infections and predation, contributing to high juvenile mortality rates.^[26]^[33]

Diet and foraging

Members of the family Grylloblattidae exhibit an omnivorous scavenging diet, primarily consisting of dead arthropods and carrion, with opportunistic consumption of live insect prey when available. Gut content analyses reveal that arthropods dominate their diet, including cold-adapted species such as tipulid flies, while laboratory observations confirm that both adults and larvae require animal-based food for growth and survival, rejecting non-animal items like algae or fungi in controlled settings. When carrion is scarce, they supplement with plant material, fungi, and decaying organic detritus, reflecting their adaptability to nutrient-poor, cold environments.^[35]^[28]^[12] Grylloblattids forage nocturnally under cover, such as rocks, downed wood, or snow surfaces, using antennae equipped with sensilla to detect prey via chemical and tactile cues before seizing it with mandibles. This slow, deliberate stalking occurs in confined glacial or alpine microhabitats, avoiding open exposure due to their low activity levels and lack of defensive structures like webs or traps. Their cold-specialized physiology supports infrequent feeding, with populations showing tolerance to prolonged periods without food through reduced metabolic demands.^[36]^[37]^[38] In contrast, Mantophasmatidae are strictly carnivorous predators, targeting small arthropods including ants, flies, caterpillars, moths, spiders, and mites through ambush tactics in rocky crevices. Laboratory and field studies document consumption of diverse prey like Drosophila fruit flies, houseflies, cricket nymphs, and termites, with no evidence of plant or detrital feeding. They employ raptorial fore- and mid-legs to grasp and immobilize victims during rapid mandibular strikes, often consuming prey whole or biting off heads for quicker ingestion, as observed in species like Mantophasma.^[26] Mantophasmatid foraging involves a "hide-and-wait" strategy with short-distance stalking in confined spaces, relying on stealth rather than pursuit or trap-building, which aligns with their low-energy lifestyle in arid, rocky habitats. Digestive processes are efficient, with food stored in the foregut for hours and protein breakdown occurring rapidly in the midgut within about two hours, supporting their predatory efficiency despite sporadic feeding opportunities. Cannibalism occurs in dense populations or captivity, underscoring their opportunistic carnivory.^[26]

Behavior

Locomotion and activity patterns

Notoptera exhibit cursorial locomotion adapted to their terrestrial habitats, relying on running and climbing rather than jumping or flight, as they are entirely wingless. In Mantophasmatidae, a distinctive "heel-walking" gait is employed, where the distalmost tarsomere is permanently elevated off the substrate, allowing traction primarily through the proximal euplantulae on rocky or uneven surfaces for enhanced grip during short bursts of movement.^[17] Grylloblattidae, in contrast, display slower, more probing steps suited to cold, snowy environments, facilitating cautious navigation over ice or litter while foraging or retreating.^[12] Both families occasionally climb vegetation or rocks, leveraging elongated legs for stability, though sustained running is limited to brief escapes or pursuits.^[26] Activity patterns in Notoptera are predominantly nocturnal, with individuals emerging after dusk to minimize predation and desiccation risks. During the day, they hide under stones, leaf litter, or in crevices to avoid light and heat, only becoming active in cooler, humid conditions near 0–4°C for Grylloblattidae.^[27] In Mantophasmatidae, while some species show limited diurnal activity, most exhibit heightened movement and interactions post-sunset, aligning with a hide-and-wait strategy interspersed with short stalks.^[26] Seasonal rhythms peak during cooler months; Grylloblattidae in lower elevations are active from first snowfall to snowmelt in winter, while high-alpine populations forage in summer on snowfields, reflecting their cryophilic adaptations.^[12] Mantophasmatidae show increased activity during rainy seasons, correlating with nymph hatching and resource availability in arid regions.^[26] Escape responses emphasize crypsis and rapid retreat over agility, with individuals freezing in place or swiftly moving into nearby crevices upon disturbance, avoiding confrontation due to the absence of defensive structures or chemicals.^[12] Jumping and flight capabilities are absent in Grylloblattodea, while Mantophasmatodea exhibit rare, limited jumps of a few centimeters; evasion is primarily ground-based withdrawal. Energy conservation is critical in their marginal habitats, manifesting as reduced locomotion in suboptimal temperatures; Grylloblattidae become inactive during extreme cold or dryness, relying on accumulated fat reserves to endure inactivity periods.^[39] Similarly, Mantophasmatidae minimize energy expenditure by elevating arolia when idle, preventing unnecessary secretion, and exhibit low overall activity to persist in fluctuating arid conditions.^[26] Notopterans exhibit limited sociality, remaining largely solitary throughout their lives except during brief periods of mating and oviposition. Individuals do not form colonies or exhibit cooperative behaviors, though nymphs may occasionally aggregate incidentally in protective refugia such as rock crevices or under stones for shelter and thermoregulation, without structured social interactions.^[26]^[40] Courtship in Notoptera relies on tactile and chemical cues rather than acoustic signals, with stridulation absent across the order. In Grylloblattidae, mating occurs under stones or in caves, where males and females face each other and touch antennae in a stationary display to assess compatibility; if the female moves away, the male pursues her in a chase before depositing a spermatophore on the substrate for her to take up.^[41] In Mantophasmatidae, courtship involves antennal flickering to detect pheromonal signals for mate location, combined with vibrational drumming produced by abdominal tapping on the substrate, where males emit complex pulse trains and females respond with single pulses detected via leg scolopidial organs.^[26] Copulation follows rapidly, often lasting several hours to over 20 hours, with males mounting females in a false male-above position using fore- and midlegs to grasp them.^[26] Aggression in Notoptera is infrequent and primarily manifests during mating interactions rather than territorial disputes. Females in both families may exhibit defensive behaviors, such as kicking or biting intruding males during courtship attempts. Post-mating cannibalism by females consuming males is documented, potentially providing nutritional benefits, though it occurs sporadically.^[26] Territorial conflicts are rare, with individuals typically retreating from encounters via quick runs or hiding, emphasizing their solitary lifestyle.^[40]

Evolutionary history

Fossil record

The fossil record of Notoptera originates in the Late Carboniferous, approximately 305 million years ago, with early winged forms preserved primarily in coal-bearing deposits of Euramerica. The oldest known representative is Montceaupterum baillyi, a member of the family Euryptilonidae, discovered in the Gzhelian-stage Commentry Formation at Montceau-les-Mines, France, marking the earliest occurrence of this Permian-dominant family. Additional early records include rare taxa from families such as Protoperlidae and Daldubidae in tropical to temperate Euramerican assemblages, indicating an initial diversification among stem-Notoptera in humid, forested paleoenvironments.^[42]^[43] Notopteran diversity peaked during the Permian (299–252 Ma), when winged grylloblattidans became prominent components of insect faunas, often comprising a substantial proportion—up to one-third in some assemblages—and dominated by families within Eoblattida and related groups. The Euryptilonidae alone encompass 14 genera across Europe, Asia, and North America, with well-preserved forewings highlighting venational complexity adapted to flight in diverse Permian biomes. Early Permian sites, such as the Asselian-stage Goldlauter Formation in Germany (Sperbersbach and Cabarz localities), yield multiple genera like Pictoborella, Liomopterum, and Cabarzopterum, underscoring the order's radiation in lake-margin and floodplain habitats during this period of high polyneopteran abundance.^[42]^[44]^[45] Following the end-Permian mass extinction, Notoptera experienced a marked decline in diversity from the Triassic onward, accompanied by multiple wing loss events that shifted the group toward more terrestrial lifestyles. Triassic records show reduced winged forms, with only a few families persisting into the Mesozoic. In the Middle Jurassic (approximately 165 Ma), mantophasmatid-like fossils appear, exemplified by Juramantophasma sinica from the Jiulongshan Formation at Daohugou, Inner Mongolia, China, featuring apomorphic traits such as large fan-like arolia and sclerotized tarsal processes indicative of early divergence within the order. Cretaceous inclusions (around 99 Ma) from Burmese amber in Myanmar preserve winged grylloblattids, including Zygogrylloblatta longipalpa and members of a newly recognized family, displaying modern mouthpart configurations like elongated maxillary palpi, sickle-shaped laciniae with setal brushes, and robust mandibles suited for predatory feeding.^[46]^[47]^[11]^[48] The extinct diversity of Notoptera exceeds 100 described species across more than 40 families, spanning from Carboniferous shales and coal measures to Mesozoic amber and lacustrine deposits, which collectively reveal habitat transitions from swampy lowlands to upland forests and arboreal niches. This preservation bias highlights adaptive shifts, with amber capturing late-surviving winged forms in tropical settings, while earlier shale fossils document dominance in Paleozoic wetlands.^[49]^[44]

Phylogenetic position

Notoptera occupies a basal position within the Polyneoptera clade of insects, a major lineage of Neoptera characterized by flexible wing bases and other shared traits. Phylogenetic analyses consistently place Notoptera as monophyletic, with Grylloblattidae (ice crawlers) and Mantophasmatidae (gladiators or rock crawlers) forming sister groups, a relationship supported by both morphological and molecular data. This sister-group status reflects shared synapomorphies such as reduced wing venation and specialized thoracic structures, though extant species are apterous, indicating independent wing loss from winged ancestors known from the fossil record.^[9]^[7] The precise placement of Notoptera relative to other polyneopteran orders varies across studies. In some phylogenomic analyses, Notoptera emerges as sister to Orthopterida (comprising Orthoptera and Phasmatodea), highlighting early divergences among hemimetabolous insects with orthopteroid-like traits. Alternative reconstructions position it as sister to Plecoptera (stoneflies), based on shared primitive features like filiform antennae and certain genitalic structures, underscoring ongoing debates in lower neopteran relationships. These inconsistencies arise from differences in dataset composition and analytical methods, but all affirm Notoptera's position among the "lower" Polyneoptera.^[7]^[9] Molecular evidence has been pivotal in establishing Notoptera's monophyly since the early 2000s. Seminal studies using nuclear ribosomal genes (18S and 28S rRNA) combined with histone H3 and morphological characters confirmed the clade's integrity, rejecting broader groupings like Xenonomia that excluded certain fossil-inclusive lineages. Subsequent mitogenomic analyses, incorporating complete mitochondrial genomes, have reinforced this monophyly with high bootstrap support, while also resolving internal relationships and dating the divergence of Grylloblattidae and Mantophasmatidae to the Carboniferous period (approximately 329 million years ago). These datasets prioritize highly conserved genes to mitigate long-branch attraction artifacts common in polyneopteran phylogenies.^[9]^[6] As relict lineages, Notoptera represents surviving remnants of a Permian radiation within Polyneoptera, when diverse winged forms proliferated before mass extinctions pruned the group. Their persistence through the Permian-Triassic boundary implies ecological specialization in cold, montane, or arid habitats, providing key insights into the evolutionary stability of basal polyneopterans. This relict status underscores Notoptera's role in reconstructing the mosaic evolution of Polyneoptera, from early terrestrial adaptations to the dominance of more derived orders like Orthoptera.^[6]^[7]

History of research

Early descriptions

The first scientific description of a notopteran species occurred in 1914, when the Canadian entomologist Edmund M. Walker identified specimens collected from Banff National Park in Alberta, Canada, naming them Grylloblatta campodeiformis and establishing the family Grylloblattidae within the order Orthoptera. Walker noted the insect's elongate body, lack of wings, and superficial resemblances to both crickets (Gryllus) and cockroaches (Blatta), leading to its initial classification as an orthopteran. In 1915, G. C. Crampton proposed the ordinal name Notoptera for Grylloblatta campodeiformis, emphasizing its transitional thoracic sclerites and potential links to fossil forms as evidence of an intermediate position among polyneopteran insects. This classification highlighted its annectant nature, bridging orthopteroid groups, though the name Notoptera saw limited adoption initially. Early taxonomists often misclassified Grylloblattidae due to morphological similarities, such as the cylindrical body and cerci resembling those of earwigs (Dermaptera) or the head and leg structures akin to cockroaches (Blattodea).^[50] By the end of the 20th century, knowledge of Notoptera remained restricted to the Grylloblattidae, with approximately 10 species described, primarily from cold, alpine habitats in North America and Asia; no extant Mantophasmatidae were known at that time.^[51] These early studies laid the groundwork for recognizing Notoptera as a distinct lineage, though its exact affinities continued to puzzle researchers until molecular advancements.^[51]

Modern discoveries

The discovery of the insect order Mantophasmatodea in 2002 marked a pivotal advancement in Notoptera research, representing the first new insect order described since Grylloblattodea nearly a century earlier. Based on museum specimens from Namibia and Tanzania, researchers identified Mantophasma zephyra and M. subsolana as the inaugural species, characterized by their carnivorous habits, elongated bodies, and heel-walking posture. This finding expanded Notoptera to include a second extant suborder alongside Grylloblattodea, highlighting the order's relict status and prompting reevaluation of polyneopteran evolution. In 2005, Terry and Whiting proposed the alternative name Xenonomia for the lineage. Subsequent expeditions and morphological studies in the early 2000s revealed additional diversity, with approximately 12 species now recognized across southern and eastern Africa, primarily in arid and mountainous regions (as of 2025). Ecological investigations demonstrated that mantophasmatodeans are predatory ground-dwellers, preying on small arthropods and exhibiting stridulatory behaviors for communication, which were detailed through field observations in Namibia's Brandberg Mountains. These efforts also uncovered sexual dimorphism and mating rituals, including male nuptial gifts, underscoring the order's behavioral complexity.^[26] Fossil evidence has further illuminated Notoptera's evolutionary trajectory, with key Mesozoic discoveries bridging gaps in the lineage's history. In 2006, amber-preserved specimens from the Eocene Baltic confirmed the presence of extinct mantophasmatodeans, providing the first direct fossil link to modern forms and suggesting a broader Paleogene distribution. A 2008 report identified Jurassic fossils from China's Daohugou Beds, extending the group's record to the Middle Jurassic and indicating early diversification among polyneopterans. Most recently, a 2025 description of a winged Cretaceous ice-crawler from Myanmar amber (Zygogrylloblatta longipalpa) revealed transitional morphology between arboreal ancestors and the wingless extant Grylloblattidae, supporting an ecological shift from trees to ground habitats during the early Paleogene.^[52]^[47]^[11] Molecular phylogenetics has refined Notoptera's position within Polyneoptera, with transcriptomic and mitochondrial analyses from 2020 onward affirming its monophyly and ancient origins. A 2024 study using complete mitogenomes dated the divergence of Mantophasmatodea and Grylloblattodea to the Carboniferous (approximately 320 million years ago), aligning fossil evidence and emphasizing their relict survival amid mass extinctions. Complementary 2025 transcriptomic work on gene families revealed adaptations for cold tolerance in grylloblattodeans and predatory efficiency in mantophasmatodeans, including expansions in chemosensory and detoxification genes. These genomic insights have also facilitated new species descriptions, such as Grylloprimevala jilina from China in 2023, enhancing taxonomic resolution.^[6]^[53]^[27]

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