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Earless monitor lizard
Earless monitor lizard
Earless monitor lizard
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Earless monitor lizard
CITES Appendix II [2]
Scientific classification Edit this classification
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Squamata
Suborder: Anguimorpha
Superfamily: Varanoidea
Family: Lanthanotidae
Steindachner, 1877
Genus: Lanthanotus
Steindachner, 1878
Species:
L. borneensis
Binomial name
Lanthanotus borneensis
Earless monitor skull

The earless monitor lizard (Lanthanotus borneensis) is a semiaquatic, brown lizard native to the Southeast Asian island of Borneo. It is the only living species in the family Lanthanotidae and it is related to the true monitor lizards.[3][4][5]

Taxonomy

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The earless monitor lizard was described in 1878 by Franz Steindachner.[6] The genus name Lanthanotus means "hidden ear" and the species name borneensis refers to its home island of Borneo. The uniqueness of the species was immediately recognized and Steindachner placed it in its own family, Lanthanotidae. In 1899, George Albert Boulenger relegated it to the family Helodermatidae, together with the beaded lizards and Gila monster, on the basis of morphological similarities. Further studies were conducted in the 1950s where it was found that although it is related to Helodermatidae, this relationship is relatively distant. The similarity is in part the result of convergent evolution and they should be recognized as separate families. Both are part of a broader Anguimorpha, but the relationship among the various families has been a matter of dispute. Several earlier studies have placed the earless monitor lizard together with Helodermatidae and Varanidae (true monitor lizards) in Varanoidea.[7] More recent genetic evidence has found that the nearest relative of the earless monitor lizard is Varanidae.[8][9] Most authorities continue to recognize them as separate families as the divergence between them is deep,[6][8][9] but some have suggested that the earless monitor lizard should be included as a subfamily, Lanthanotinae, of the Varanidae.[10] Together they form a clade and its sister group is Shinisauridae; at a higher level the sister groups of these three are Helodermatidae and others families in Anguimorpha.[8][9] The most recent common ancestor diverged in the mid-Cretaceous.[5][11]

The extinct Cherminotus known from Late Cretaceous fossil remains in Mongolia has been considered a member of Lanthanotidae, but this is disputed.[12]

Distribution and habitat

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The earless monitor lizard is endemic to the Southeast Asian island of Borneo, where it is known from Sarawak in East Malaysia, as well as West and North Kalimantan in Indonesia.[13][14][15] Until late 2012, its known range in North Kalimantan was a part of East Kalimantan.[16] It was also confirmed to be found in Brunei for the first time in 2022, in the country's Temburong District.[17] Prior to the discovery, it was believed that they may occur there and has been recorded c. 100 km (60 mi) from the border.[18] There are no records from Sabah, Central Kalimantan or South Kalimantan.[15][18]

It is found in lowlands at elevations below 300 m (1,000 ft) near streams and marshes.[19][20] These are typically in rainforests, but it is also found in streams flowing through degraded habitats such as agricultural land, mature fruit tree gardens and palm oil plantations, and reportedly may occur in rice paddies.[13][15][19] The streams it inhabits are often rocky.[13][15] Its habitat is tropical with air and water temperatures that generally are about 22–29 °C (72–84 °F),[14][15] and captives reportedly prefer 24–28 °C (75–82 °F).[21] At a site with a high density of earless monitor lizards the water was clear and had a neutral pH. It is associated with the same microhabitat as Tropidophorus water skinks and in some places its range overlaps with T. brookei.[15]

Appearance

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Earless monitor lizards have a cylindrical body, long neck, short limbs, long sharp claws, small eyes, semitransparent lower eyelids, and six longitudinal rows of strongly keeled scales.[19][22] The species is extensively covered in osteoderms.[23] Despite the name, they are capable of hearing, although lack a tympanum, an ear opening and other externally visible signs of ears.[4][24] The upperparts are orangish-brown, and the underside is mottled dark brown and whitish, pale yellowish, ochre or rusty.[25][13][19] The tail is prehensile and if it is lost, it is not regenerated. The skin is shed infrequently, possibly less than once a year. There are both reports of the skin shedding in one piece (similar to snakes),[22] or in smaller pieces (as typical of lizards).[26] Overall the sexes are alike, but males have a distinctly broader head and broader tail base than females.[15] The differences between the sexes are clearly noticeable from an age of about three years.[27] They sometimes oscillate the throat (similar to frogs) and the forked tongue is sometimes flicked (similar to snakes). They can make a gentle, squeaky vocalization.[15]

Size

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Adult earless monitor lizards typically have a snout-to-vent length (SVL) of about 20 cm (8 in),[19] and a total length of about 40 cm (16 in).[26] Eighteen wild individuals, six males and twelve females, ranged from 15.6 to 22 cm (6.1–8.7 in) in SVL, 17.4 to 22.1 cm (6.9–8.7 in) in tail length (disregarding one individual missing much of its tail), and 48 to 120 g (1.7–4.2 oz) in weight (disregarding one sickly and skinny individual). Among these, the largest total length (SVL+tail) was a male that measured 44.1 cm (17.4 in), which also is the longest recorded in the wild.[15] A specimen collected in the 1960s has a total length of 51 cm (20 in),[25] and near the time of its death an individual kept at the Bronx Zoo from 1968 to 1976 had a total length of 47 cm (18.5 in) and weighed 209 g (7.4 oz), but it was highly obese.[28] When hatching the total length of the young is about 7–14 cm (3–6 in).[14][29][30] When one year old, their total length is about 23–25 cm (9–10 in).[31] The record size of earless monitor is 55 cm.[32]

Behavior

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Earless monitor lizards are generally strictly nocturnal animals, although exceptional daytime observations in the open have been reported.[13][15] The day is usually spent near water in burrows that can be up to 30 cm (1 ft) long or under logs, rocks or vegetation.[5][19] They are generally quite inactive and not agile, but can make surprisingly fast spurts when startled,[15] and will rapidly catch prey items placed in front of them.[29] During one study where 19 individuals were located during the night, about half were in the water and the other half near water on land.[15] In captivity they sometimes remain virtually immobile underwater for hours, periodically lifting the nose above the water's surface to breathe.[33] When underwater, the semitransparent lower eyelids are generally closed, covering the eyes.[15] It has been speculated that the prehensile tail is wrapped around stones, roots and other things underwater to avoid being swept along during floods.[29]

Bite

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See also: Toxicofera

Although generally docile and inactive when handled, males are usually more aggressive than females when caught. In one case, a scientist received a deep bite in his finger, but did not experience any effects that could indicate a presence of venom in the bite (unlike the related and venomous beaded lizards, Gila monster and some monitor lizards).[15] This supported decades-old dissection studies where no venom glands or grooves in the teeth were found.[25] Others kept in captivity were found to bite often, resulting in wounds that are relatively deep (compared to those from similar-sized lizards) and can bleed extensively,[29] with blood clotting reportedly being slower than in normal wounds.[26] Recent studies have found both venom glands,[34] and toxic compounds in the bite of this species. The main components are kallikreins (to a lesser degree CRiSP) with the primary effect being the cleaving of fibrinogen, which is important for blood clotting.[35] However, this effect is quite weak in the venom of the earless monitor lizard compared to that of many other venomous reptiles, including some of the true monitor lizards.[36]

Feeding

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They typically feed on earthworms, crustaceans and fish.[19] In captivity, they will eat fish (both whole and pieces), earthworms, squid, shrimp, tadpoles, yolk from green sea turtle eggs, pieces of pig and chicken liver, baby mice and mussels, but refuse to take bird eggs and legs of frog.[15][28][30][33] In captivity adults typically eat once or twice per week, but sometimes enter longer periods where they do not feed.[33] Unusually for a lizard, they can swallow prey while submerged underwater. The only other monitor species reported to do this is Mertens' water monitor.[28] They appear to be able to do this by draining water from their nostrils, similar to turtles.[29]

Breeding and life cycle

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Like their closest relatives, they are oviparous, although little is known about their reproduction.[4] Based on captive observations a pair will mate repeatedly over a period of a few months, with each session lasting for hours.[37] In one case, a single mating lasted 44 hours.[29] They mate in the water.[37][38] In the wild mating has been seen in February,[5] and a female caught in April was likely gravid.[15] The 2–12 (average 8) oval eggs measure about 3 cm (1.2 in) long and have a leathery white shell.[25][19][29][39] They are deposited on land.[39] In captivity the eggs hatch after about three months at a temperature of 27 °C (81 °F).[29][30] Adult males are likely territorially aggressive, as a survey of a locality found twice as many females as males, and most of the males (but no females) had various injuries, such as loss of toes or tail, and scarring on the head or neck.[15] In captivity, young up to 6 months old have been kept in groups, and adults have been kept singly, as pairs or a single male with several females; more than one adult male causes problems.[33] The lifespan is unknown, but—despite the very limited knowledge of reptile keeping at the time—an individual that entered captivity as a young adult in the 1960s lived for more than 7.5 years after its capture (growing from 38.2 to 47 cm or 15.0 to 18.5 in in total length),[28] and others have reportedly surpassed a decade in captivity.[25]

Status and conservation

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The earless monitor lizard has been rated by the IUCN as endangered (its range covers less than 500 km2 or 190 mi2).[20] The species is usually considered very rare, but it is easily overlooked and as recently as 1999 the only published confirmed records were from Sarawak.[25] Confirmation from Kalimantan only appeared later.[15] In some areas locals are unaware of its presence or consider it rare, but in others it may be common. At one site in West Kalimantan, 17 of 21 locals asked were aware of its presence and most of these considered it common. At three other sites in the region the majority asked were aware of its presence, but less than half considered it common.[13] Elsewhere in West Kalimantan, a three-night survey of a 400 m (1,300 ft) long section of a stream, as well as two adjacent streams, located 19 earless monitor lizards, representing an unusually high density for a lizard of this size. Despite this high density in a stream used by locals for washing, fishing and as a source of drinking water, they only reported seeing the species very rarely and some had never seen it.[15] Nevertheless, at present the earless monitor lizard is only known for certain from a relatively small number of sites.[18][20]

About 100 museum specimens are known and most major natural history museums have one or more in their collection.[25] These were generally collected in the 1960s–1980s or earlier,[14] often during floods when earless monitor lizards were swept along the current and ended up in fishing traps.[25][22] From the 1960s to the 1990s small numbers entered the pet trade.[28] In 2012 it was featured in a Japanese reptile keepers magazine and in the following years a larger number of individuals entered captivity.[18][40] From May 2014 to October 2015 at least 95 earless monitor lizards appeared in the trade in Asia (Hong Kong, Indonesia, Japan and Malaysia), Europe (Czech Republic, France, Germany, Netherlands, Russia, Ukraine and the United Kingdom) and the United States.[41] Collecting the species from the wild is illegal; the earless monitor lizard has been protected in Malaysia since 1971, in Brunei since 1978 and in Indonesia since 1980. Penalties range from a fine of US$1,600 and one year's imprisonment (Brunei) to $7,850 and three years' imprisonment (Malaysia), to $8,600 and five years' imprisonment (Indonesia).[41] As a precaution some scientists that have discovered individuals in the wild have refused to provide the exact location, only describing it in very broad terms, citing fears of alerting wildlife traders.[13][15] In 2015, a smuggler was caught in an Indonesian airport with 8 individuals and in 2016 another was caught in an Indonesian airport with 17 individuals.[40] This trade is supported by the very high price. When first entering the market in Japan, a pair sold for ¥3 million (more than US$25,000). Although the price has since fallen by more than 90% due to increased availability, it remains valuable.[40] Significant declines in price have also been noted elsewhere.[42] Unlike all other monitor species, the earless monitor lizard was not listed on CITES, which would restrict trade at an international level.[40][41] In 2016 it was proposed that it should be placed on CITES Appendix I,[18] and in 2017 it was afforded a level of protection when placed on Appendix II (wild individuals cannot be exported for commercial purposes).[43]

The first confirmed captive breeding was at a zoo in Japan in 2014.[28][29] A couple of years later a few European zoos initiated a breeding program; in 2017 it was bred at Schönbrunn Zoo in Austria, and in 2018 it was bred a Prague Zoo in the Czech Republic and Moscow Zoo in Russia.[30][44][45][46] There have been other breeding reports by private keepers and captive bred individuals have been offered for sale, but some of these may not involve genuine cases of captive breeding.[20]

Habitat loss represents another serious threat, as forests in Borneo rapidly are being replaced by oil palm plantations.[15][22][40] However, the earless monitor lizard can survive in high densities in areas surrounded by degraded habitats (including oil palm plantations), and rocky streams, possibly its preferred habitat, are relatively unaffected by humans.[15]

References

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Earless monitor lizard

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from Grokipedia
The earless monitor lizard (Lanthanotus borneensis) is a endemic to , distinguished by the complete absence of external ear openings while retaining the ability to detect sound vibrations. As the sole living species of the family Lanthanotidae, it occupies a basal position within the (), featuring primitive morphological traits such as a long neck, short limbs, and keeled dorsal scales that echo ancestral forms preserved in the fossil record. This elusive species inhabits humid, lowland rainforest streams and adjacent riparian zones across Brunei, Indonesia (Kalimantan), and Malaysia (Sarawak), where it exhibits a primarily nocturnal, subfossorial lifestyle—burrowing in moist soil or concealing itself in rock fissures and leaf litter during daylight hours. Adults typically measure 40–50 cm in total length, with a cylindrical body adapted for swimming and digging, small eyes suited to low-light conditions, and a diet comprising aquatic invertebrates, fish, and small vertebrates captured via ambush predation near water edges. Like other varanids, it possesses mandibular glands secreting toxic proteins, conferring mild venomous capabilities that aid in subduing prey. Classified as Endangered by the , L. borneensis faces acute threats from , , and illicit international trade, with exacerbating its low and restricted distribution spanning less than 20,000 km². Despite total legal protection in all range states and inclusion in Appendix II, enforcement challenges persist, as evidenced by sporadic seizures of smuggled specimens and the scarcity of verified wild encounters—fewer than 200 documented over 150 years. Recent proposals for enhanced regulatory measures, including U.S. Endangered Species Act listing, underscore the urgency of preservation and initiatives to avert further decline.

Taxonomy and phylogeny

Classification and nomenclature

The earless monitor lizard is classified within the domain Eukarya, kingdom Animalia, phylum Chordata, class Reptilia, order , suborder , family Lanthanotidae, genus Lanthanotus, and species L. borneensis. It represents the sole extant species in its monotypic genus and family, positioning it as a basal member of the superfamily alongside true monitors (family ). The binomial name Lanthanotus borneensis was formally established by Austrian ichthyologist Franz Steindachner in 1878, based on specimens collected from . The genus name derives from Greek lanthanein ("to hide" or "conceal") and ōtos ("ear"), reflecting the absence of external ear openings despite functional internal auditory structures. The specific epithet borneensis denotes its endemic distribution on the island of . Known synonyms include Lanthonotus borneensis Steindachner, 1877 (a typographical variant from an initial ). No subspecies are recognized, underscoring its taxonomic isolation. The International Union for Conservation of Nature (IUCN) lists it as Endangered (EN), though this pertains to conservation rather than systematic placement.

Evolutionary relationships

The earless monitor lizard (Lanthanotus borneensis), the sole extant member of the family Lanthanotidae, represents the sister taxon to , the family encompassing all true monitor lizards of the genus Varanus. This phylogenetic placement situates Lanthanotidae within the superfamily of the suborder , a branch of characterized by robust skulls, forked tongues, and specialized predatory adaptations. Both molecular analyses of mitochondrial and nuclear genes and morphological studies of cranial and postcranial features corroborate this close affinity, with Lanthanotus diverging from the Varanus lineage prior to the radiation of modern monitor subgenera. The divergence between Lanthanotidae and is estimated to have occurred during the mid-to-late , approximately 80–100 million years ago, based on calibrations incorporating constraints from stem-varanoid taxa. This split predates the diversification of Varanus into its biogeographically widespread clades, which subsequently colonized , , , and associated islands. Lanthanotus retains several plesiomorphic (ancestral) traits absent or reduced in most Varanus species, including the lack of external openings, a more compact body form with shorter limbs, and semi-aquatic habits that may reflect an early anguimorph condition before the evolution of terrestrial in monitors. At a broader level, the Lanthanotidae–Varanidae clade forms the to Shinisauridae, comprising the (Shinisaurus crocodilurus), within the expanded ; this topology is robustly supported by concatenated genomic datasets resolving deep anguimorph relationships. Fossil relatives, such as the Cherminotus from and early stem-varanids, indicate that the lineage's origins trace to Laurasian landmasses, with Lanthanotus as a population in preserving a morphology bridging primitive anguimorphs and derived monitors. These relationships underscore Lanthanotidae's key role in reconstructing the evolutionary transitions toward the active foraging and venom-delivery systems seen in .

Physical characteristics

External morphology

The earless monitor lizard (Lanthanotus borneensis) possesses a cylindrical, elongated body adapted for and burrowing lifestyles, featuring a long neck, short limbs, and a flattened head without external ear openings or a gular fold, distinguishing it from typical monitor lizards. Small eyes with reduced nostrils and semitransparent lower eyelids further characterize the head, alongside a typical of varanids. The dorsal surface exhibits six longitudinal rows of enlarged, , contributing to a rough, lumpy texture that facilitates by adhering to dirt in humid environments. Short limbs terminate in long, sharp claws suited for gripping substrates, while the laterally compressed, —incapable of regeneration—enables anchoring in fast-flowing streams. Coloration varies from dark orange-brown to or rusty hues dorsally, with a paler underside, enhancing in Borneo's forested, riverine habitats. The skin sheds infrequently, potentially less than once annually, reflecting low metabolic demands.

Size and sexual dimorphism

Adult Lanthanotus borneensis specimens typically measure 20 cm in snout-to-vent length (SVL), with total lengths averaging 40 cm. Maximum recorded total lengths reach approximately 50 cm in wild individuals. Body mass data remain limited, with estimates for adults up to 113 grams based on captive observations. Sexual dimorphism manifests primarily in cranial and caudal morphology rather than overall body size. Males possess broader heads and distinctly enlarged tail bases, the latter resulting from hemipenal bulbs. These traits facilitate sex identification in field studies, though subtle differences in head width require careful measurement for confirmation. No significant disparities in SVL or total length between sexes have been consistently documented, distinguishing L. borneensis from many varanid monitors where males often grow larger. ![Lanthanotus skulls][float-right](./assets/Lanthanotus_skulls_(cropped)

Distribution and habitat

Geographic range

The earless monitor lizard (Lanthanotus borneensis) is endemic to the island of in , with a restricted distribution confined to its northern and northwestern lowlands. Records confirm its presence in the Malaysian state of , the Indonesian provinces of and , and the Sultanate of . The species has not been documented in (Malaysia) or other regions of , such as Central or (Indonesia), despite surveys. Known localities include riparian zones along streams in Sarawak's peat swamp forests and areas, as well as similar habitats in near the basin. In , sightings are sparse but occur in lowland rainforests bordering . Brunei's populations are limited to a few sites in Tutong and Belait districts, reflecting the overall fragmented and localized nature of the range. Elevational records do not exceed 300 meters above , underscoring the species' lowland specialization. Habitat from and has likely reduced effective range connectivity since early 20th-century descriptions.

Habitat preferences and microhabitats

The earless monitor lizard (Lanthanotus borneensis) inhabits lowland tropical rainforests across , primarily at elevations below 300 meters, where it favors riparian zones associated with clear, rocky streams and marshes. These preferences align with its lifestyle, enabling access to aquatic prey and refuge from terrestrial threats, as evidenced by field records from and showing consistent occurrence near permanent water bodies in humid environments. While forested habitats provide proportionally more suitable area (73.7% versus 39.6% in oil palm plantations), the species tolerates some anthropogenic modification, with sightings in plantation edges proximate to streams, though population densities appear lower in disturbed sites. Microhabitats utilized include stream banks with rocky substrates and overhanging dense offering canopy cover, which support cryptic and reduce exposure to diurnal predators. Observations indicate no strong reliance on specialized structures for , with individuals basking on exposed rocks or submerged partially in shallow s during daylight hours, suggesting behavioral flexibility within available riparian features rather than fixed microsite selection. Shelter sites often comprise natural crevices under boulders, fallen logs, or leaf litter accumulations along water margins, occasionally supplemented by excavated burrows, facilitating nocturnal retreats and deposition in moist, protected depressions. These microhabitat choices correlate with hydrological stability, as rocky streams remain relatively unaffected by upstream compared to softer-soil floodplains.

Behavior and ecology

Daily activity and locomotion

The earless monitor lizard (Lanthanotus borneensis) exhibits primarily nocturnal activity patterns, with foraging and movement occurring mainly during twilight and nighttime hours to minimize exposure to diurnal predators and high daytime temperatures in its habitat. Individuals remain concealed in burrows, under leaf litter, or near stream banks during daylight, showing no evidence of basking behavior and limiting surface activity to brief periods if needed for . Observations in the wild confirm regular nocturnal excursions to nearby streams for hydration and potential hunting, with shelter departure timed to coincide with . Locomotion in L. borneensis is adapted to its semiaquatic and subfossorial lifestyle, featuring serpentine undulations of the elongated trunk for propulsion through , , and over uneven substrates. On , movement involves low-slung crawling with relatively weak limbs providing auxiliary support, while the blunt head aids in displacing during burrowing or in dense . In aquatic environments, the species demonstrates proficient via lateral thrusts, enabling submersion for extended periods and traversal of creeks and streams integral to its habitat. Telemetry data from , , indicate modest daily displacement, with maximum recorded movements of 74 meters, reflecting a of localized within small home ranges rather than extensive travel.

Foraging and diet

The earless monitor lizard (Lanthanotus borneensis) maintains a carnivorous diet focused on aquatic and semi-aquatic prey, including earthworms, crustaceans such as (Macrobrachium spp.) and , and small like (Clarias cf. tejsmanni). Stomach contents from wild specimens confirm these items as primary components, reflecting to humid, streamside habitats where such prey is abundant. Foraging is predominantly aquatic, with individuals pursuing prey underwater in creeks and muddy substrates, often consuming earthworms and small directly in the or along banks. Observations indicate a crepuscular pattern, with feeding concentrated in short bouts on exposed mudflats, leveraging low-light conditions for cryptic hunting. In captive settings, which mirror semi-natural conditions, readily accept frog meat and exhibit predation on species like the rice field (Fejervarya limnocharis), suggesting amphibians may supplement the diet opportunistically. This strategy aligns with their lifestyle, emphasizing tactics over active pursuit due to their relatively lethargic demeanor.

Defensive behaviors and bite

The earless monitor lizard (Lanthanotus borneensis) primarily employs passive defensive strategies, relying on its cryptic coloration, habits, and tendency to flee into water or burrows when threatened in . Observations of captured individuals indicate a generally docile response to handling, with limited active aggression such as hissing or tail lashing reported, unlike many varanid monitors. Some specimens exhibit thanatosis, a behavioral adaptation involving feigned death through immobility, which may serve to discourage further predation or handling. Sexual dimorphism influences defensive responses, with males displaying heightened compared to females when restrained, including attempts to bite handlers. This is context-specific to capture stress rather than routine territorial defense. No quantitative data on bite force exists for the , but its —featuring sharp, recurved teeth—enables tissue laceration similar to that in other small monitors. The lizard delivers a venomous bite via an enlarged mandibular gland homologous to those in reptiles, secreting proteins with weak coagulotoxic activity that mildly disrupts blood clotting. This venom likely aids in subduing prey such as and small rather than serving as a potent antipredator mechanism, with effects far less pronounced than in advanced varanids like Varanus varius. Documented envenomations are rare but include deep requiring stitches, with no systemic toxicity reported beyond localized damage.

Reproduction and development

Mating systems

Mating in the earless monitor lizard (Lanthanotus borneensis) primarily occurs and has been observed in captive pairs, with limited documentation due to the species' cryptic habits. Males initiate by repeatedly nudging the female's region with their snout, prompting the female to respond before copulation begins. During , which can last several hours per session and recur over a few months within a pair, the partners' bodies and tails entwine multiple times, without aggressive biting. In one documented case, a single session extended to six hours. Captive breeding records indicate year-round potential, modulated by environmental factors like , though wild observations suggest a seasonal peak, with pairings noted in . The remains incompletely characterized, lacking evidence of strict , , or pronounced male-male competition; repeated pairings within observed dyads imply at least within short-term associations, akin to patterns in related varanids, but multiple partnering in the wild cannot be confirmed without further field data. Observations derive from experienced herpetoculturists, including Manfred Reisinger's 2015 captive study of a .

Egg-laying and incubation

The earless monitor lizard is oviparous, with females depositing clutches of 2 to 8 oval eggs possessing leathery shells, each measuring approximately 30 mm in length. In captivity, clutch sizes have occasionally exceeded this range, reaching up to 12 eggs, though averages align closer to 6–7 based on documented breedings. Eggs laid in controlled settings measure about 3 cm by 2 cm and weigh 4.7–5.0 g, with oviposition typically occurring several weeks post-mating, such as in July following June pairings. Wild oviposition remains undocumented due to the species' elusive nature and limited field observations, but captive evidence suggests females select moist, concealed terrestrial sites for deposition. Incubation in captivity requires temperatures of 27–31 °C (80.6–87.8 °F), yielding hatchlings after 62–90 days, with the full interval from fertilization to emergence exceeding six months. Successful examples include a 2014 hatching at iZoo in , marking the first captive reproduction, and a 2022 clutch of seven eggs at that hatched in October after roughly 90 days. Hatchlings emerge at total lengths of 7–14 cm, independent and capable of feeding shortly thereafter, though survival rates in early captive efforts were variable due to nascent husbandry protocols.

Growth and lifespan

Hatchlings of the earless monitor lizard (Lanthanotus borneensis) measure 7–14 cm in total length upon emergence from eggs that are approximately 3 cm long. In captive conditions, juveniles grow rapidly, attaining 23–25 cm total length after , though data on wild growth rates remain unavailable due to the species' cryptic habits and low encounter rates. Adults typically reach a maximum total length of 40–50 cm, with slender bodies and relatively short limbs reflecting semiaquatic adaptations that persist from juvenile stages. Limited observations suggest similar to other varanoids, but precise ontogenetic trajectories, including sexual size dimorphism, are undocumented in peer-reviewed studies owing to the rarity of specimens. Lifespan in the wild is unknown, as no long-term field studies exist for this elusive endemic to Borneo's riparian habitats. Captive records indicate potential exceeding 7.5 years, with one individual surviving beyond this duration after entering as a , though early husbandry challenges likely limited earlier records. These estimates derive from sporadic zoo and private breeding efforts, such as those initiated in , highlighting gaps in knowledge that hinder conservation assessments.

Conservation and human interactions

Population status and threats

The earless monitor lizard (Lanthanotus borneensis) is classified as Endangered on the of Threatened Species, with populations inferred to be declining. No comprehensive estimates of global population size exist, though the species is known from fewer than 10 locations with an area of occupancy under 2,000 km². Historical records indicate only about 150 specimens collected over a century, reflecting its rarity and elusiveness in the wild. Primary threats include habitat loss from , driven by logging, agricultural expansion such as plantations, and , which degrade lowland forests and wetlands essential to the species across . Overcollection for the international pet trade exacerbates declines, with thousands of individuals reportedly seized in trafficking operations since the despite legal protections in , , and . In August 2025, the U.S. Fish and Wildlife Service proposed listing the species as threatened under the Endangered Species Act, citing inadequate regulatory mechanisms to curb trade and habitat degradation. Ongoing research efforts, including eDNA surveys, aim to better quantify population trends and habitat requirements, but data gaps persist due to the lizard's cryptic nature and remote distribution.

Regulatory protections and international trade

The earless monitor lizard (Lanthanotus borneensis) is regulated under Appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (), following its inclusion via a family-level listing for Lanthanotidae at the 17th in , with the regulation taking effect in January 2017. This status mandates permits from range states and import permits from destinations to verify that trade does not detrimentally affect wild populations, accompanied by a zero annual quota for wild-caught specimens intended for commercial purposes. In its native range across , , and (including and ), the species receives full legal protection prohibiting capture, possession, and trade, with penalties including fines up to MYR 25,000 (approximately USD 5,800 as of 2025 exchange rates) and imprisonment for up to three years in , and equivalent prohibitions under wildlife laws in and since at least the late 1970s in some jurisdictions. These domestic bans aim to curb for local and international markets, though enforcement challenges persist due to remote habitats and cross-border . On August 14, 2025, the U.S. Fish and Wildlife Service proposed classifying L. borneensis as threatened under the Endangered Species Act, invoking a special 4(d) rule that would prohibit U.S. import, export, and interstate sale of wild-sourced individuals while permitting regulated commerce in captive-bred specimens documented via breeding facilities. This proposal, open for public comment until October 14, 2025, responds to documented illegal trafficking volumes, with hundreds of specimens seized in and between 2014 and 2021 despite controls. International trade data reported to CITES indicate minimal legal exports post-2017, primarily non-commercial specimens for scientific or zoological purposes, underscoring the Appendix II framework's role in restricting commercial exploitation while highlighting gaps in curbing illicit pet trade demand from collectors.

Captive breeding efforts and controversies

The first reported captive hatching of Lanthanotus borneensis occurred at iZoo in on July 10, 2014, with the facility claiming to have produced the world's initial offspring from a , though the legal origin of the parents remains unverified due to the absence of export permits from range countries. Subsequent efforts expanded to European zoos, where acquired seven specimens (one adult female and six hatchlings) from iZoo in December 2016 and achieved its first breeding success in 2018, hatching five individuals; by 2022, it had reared a total of 31 offspring, with clutches distributed to other institutions including zoos in , , , Pilsen, New Orleans, and Beauval between 2019 and 2021. in reported breeding success in March 2017, marking it as the second such European facility. Private breeders have also documented sporadic successes, with videos and accounts from hobbyists demonstrating annual clutches as recently as November 2024, potentially contributing to reduced market prices for specimens—from approximately €8,167 in 2014 to €900 by 2020—by increasing availability of purportedly captive-produced individuals. However, formal programs remain absent, as noted in documentation from 2016, with reproductions described as ad hoc rather than systematically managed through studbooks or genetic monitoring. Controversies surrounding these efforts primarily involve the provenance of founder animals and the potential for zoos to facilitate illegal trade laundering. Accredited zoos, including European Association of Zoos and Aquaria (EAZA) members, have acquired L. borneensis without established breeding protocols or verification of captive origins, raising suspicions that wild-caught lizards smuggled from —where no legal international exports are permitted—are being misrepresented as captive-bred to comply with Appendix II regulations. Critics, including herpetologists, argue that public displays in zoos stimulate demand among collectors, indirectly fueling despite breeding claims, as evidenced by ongoing seizures of wild specimens in and the U.S.; for instance, a 2021 analysis found no proof that zoo-hatched lizards were verifiably from captive lineages, and initial Japanese breeding stock likely derived from undocumented imports. Proponents of captive efforts counter that verified reproductions, such as Prague Zoo's multi-clutch outputs, demonstrate feasibility for conservation breeding to alleviate wild harvest pressures, though independent genetic audits are lacking to confirm parentage. These debates underscore broader challenges in reptile conservation, where high-value "holy grail" species like L. borneensis attract both genuine husbandry advances and opportunistic trade circumvention.

References

  1. https://brill.com/view/journals/amre/44/4/article-p509_9.xml
  2. https://reptile-database.reptarium.cz/species?genus=lanthanotus&species=borneensis
  3. https://animaldiversity.org/accounts/Lanthanotidae/
  4. https://iucn-mlsg.org/lanthanotus-borneensis/
  5. https://www.researchgate.net/publication/346631712_The_earless_monitor_lizard_Lanthanotus_borneensis_-A_venomous_animal
  6. https://earth.org/?endangered-species=endangered-species-spotlight-the-borneo-earless-monitor
  7. https://cites.org/sites/default/files/eng/cop/17/prop/060216/E-CoP17-Prop-32.pdf
  8. https://www.fws.gov/press-release/2025-08/us-fish-and-wildlife-service-proposes-threatened-status-borneo-earless
  9. https://www.federalregister.gov/documents/2025/08/14/2025-15491/endangered-and-threatened-wildlife-and-plants-threatened-species-status-with-section-4d-rule-for-the
  10. https://www.gbif.org/species/144098421
  11. https://www.inaturalist.org/taxa/36062-Lanthanotus-borneensis
  12. https://www.researchgate.net/publication/354528678_Lanthanotus_borneensis_The_IUCN_Red_List_of_Threatened_Species2021
  13. https://a-z-animals.com/animals/earless-monitor-lizard/
  14. https://pmc.ncbi.nlm.nih.gov/articles/PMC8819366/
  15. https://www.sciencedirect.com/science/article/abs/pii/S0041010120304578
  16. https://www.biorxiv.org/content/10.1101/2020.02.02.931188v1.full-text
  17. https://digimorph.org/specimens/Lanthanotus_borneensis/ATOL/
  18. https://bmcecolevol.biomedcentral.com/articles/10.1186/1471-2148-13-93
  19. https://repository.si.edu/server/api/core/bitstreams/35ec1d05-0c2b-43cc-9fd8-3356bec6a4bb/content
  20. https://www.pierrewildlife.com/searchspecies/reptiles/lizards/monitors/lanthanotusborneensis/
  21. https://www.livescience.com/animals/lizards/earless-monitor-lizards-the-holy-grail-of-reptiles-that-looks-like-a-mini-dragon
  22. https://herpetion.com/blogs/lizards/lanthanotus-borneensis
  23. https://www.borneo-taubwaran.de/en/description/description/
  24. https://www.traffic.org/site/assets/files/8545/earless-monitor-lizard-trade.pdf
  25. https://usark.org/wp-content/uploads/2023/08/earless-petition.pdf
  26. https://www.academia.edu/32375444/HIDDEN_IN_THE_HEART_OF_BORNEO_SHEDDING_LIGHT_ON_SOME_MYSTERIES_OF_AN_ENIGMATIC_LIZARD_FIRST_RECORDS_OF_HABITAT_USE_BEHAVIOR_AND_FOOD_ITEMS_OF_Lanthanotus_borneensis_STEINDACHNER_1878_IN_ITS_NATURAL_HABITAT
  27. https://pmc.ncbi.nlm.nih.gov/articles/PMC8840268/
  28. https://cites.org/sites/default/files/eng/com/ac/28/E-AC28-22-05.pdf
  29. https://www.researchgate.net/publication/316060277_Hidden_in_the_Heart_of_Borneo-shedding_light_on_Some_Mysteries_of_an_Enigmatic_Lizard_First_Records_of_Habitat_Use_Behavior_and_Food_Items_of_Lanthanotus_borneensis_Steindachner_1878_in_Its_Natural_Ha
  30. https://www.researchgate.net/publication/391571599_Home_Range_Size_and_Patterns_of_Movement_in_Bornean_Earless_Monitors_Lanthanotus_borneensis_in_Sarawak_Borneo
  31. https://www.biotaxa.org/hn/article/view/76454/75549
  32. https://www.researchgate.net/publication/375518528_Thermal_biology_of_Lanthanotus_borneensis_Lanthanotidae_in_Sarawak_Borneo
  33. https://pdfs.semanticscholar.org/7456/7087a1d4015feebe6e13344c6fef488dd614.pdf
  34. https://www.researchgate.net/publication/357420637_FIRST_REPORT_ON_THE_FEEDING_BEHAVIOR_OF_EARLESS_MONITOR_LANTHANOTUS_BORNEENSIS_AND_ITS_PREDATION_ON_RICE_FIELD_FROG_FEJERVARYA_LIMNOCHARIS_IN_A_CAPTIVE_ENVIRONMENT
  35. https://ejournal.brin.go.id/treubia/article/view/9724
  36. https://pubmed.ncbi.nlm.nih.gov/33245962/
  37. https://www.borneo-taubwaran.de/en/keeping/mating/
  38. https://reptilesmagazine.com/borneo-earless-monitor-the-importance-for-captive-breeding/
  39. https://animalia.bio/earless-monitor-lizard
  40. https://www.borneo-taubwaran.de/en/keeping/oviposition-incubation-and-hatching/
  41. https://www.borneo-taubwaran.de/en/keeping/raising/
  42. https://www.traffic.org/site/assets/files/3010/traffic_pub_bulletin_27_2_earless_monitor_lizards.pdf
  43. https://news.mongabay.com/short-article/us-proposes-threatened-listing-for-widely-trafficked-borneo-earless-monitor/
  44. https://www.rufford.org/projects/amat-ribut/application-of-edna-for-conservation-population-and-habitat-characteristics-assessment-of-bornean-earless-monitor-lanthanotus-borneensis-in-west-kalimantan
  45. https://cites.org/eng/taxonomy/term/4125
  46. https://www.sciencedirect.com/science/article/pii/S2351989418303986
  47. https://www.researchgate.net/figure/First-reported-offspring-hatched-in-captivity-at-the-iZoo-Japan_fig4_265471602
  48. https://reptilesmagazine.com/5-earless-monitor-lizards-hatched-at-prague-zoo/
  49. https://www.youtube.com/watch?v=-02qwpCQeds
  50. https://natureconservation.pensoft.net/article/65124/
  51. https://www.nationalgeographic.com/animals/article/an-obscure-lizard-reveals-zoos-may-indirectly-play-role-in-animal-trafficking
  52. https://blog.pensoft.net/2021/06/25/are-zoos-inadvertently-complicit-in-wildlife-trade-the-case-of-a-rare-borneo-lizard/
  53. https://www.researchgate.net/publication/350022228_The_earless_monitor_lizard_Lanthanotus_borneensis_in_European_zoos_-_past_present_perspectives
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