Earless monitor lizard

File:Lanthanotus skulls (cropped).png

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.<ref>Template:NRDB family</ref><ref name=EoR>Template:Cite book</ref><ref name=Das2013>Template:Cite journal</ref>

Taxonomy

The earless monitor lizard was described in 1878 by Franz Steindachner.<ref name=ReptileDatabase>Template:NRDB species</ref> The genus name Lanthanotus means "hidden ear" and the species name borneensis refers to its home island of Borneo.<ref name="Sprackland1999">Template:Cite journal</ref> 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.<ref name="Sprackland1999" /> 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.<ref name="Sprackland1999" /> 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.<ref name=Ast2001>Template:Cite journal</ref> More recent genetic evidence has found that the nearest relative of the earless monitor lizard is Varanidae.<ref name=Wiens2012>Template:Cite journal</ref><ref name=Pyron2013>Template:Cite journal</ref> Most authorities continue to recognize them as separate families as the divergence between them is deep,<ref name=ReptileDatabase/><ref name=Wiens2012/><ref name=Pyron2013/> but some have suggested that the earless monitor lizard should be included as a subfamily, Lanthanotinae, of the Varanidae.<ref>Template:Cite journal</ref> 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.<ref name=Wiens2012/><ref name=Pyron2013/> The most recent common ancestor diverged in the mid-Cretaceous.<ref name=Das2013/><ref>Template:Cite journal</ref>

The extinct Cherminotus known from Late Cretaceous fossil remains in Mongolia has been considered a member of Lanthanotidae, but this is disputed.<ref>Template:Cite journal</ref>

Distribution and habitat

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.<ref name=Yapp2012>Template:Cite journal</ref><ref name=Vergner2013>Template:Cite journal</ref><ref name=Langner2017>Template:Cite journal</ref> Until late 2012, its known range in North Kalimantan was a part of East Kalimantan.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> It was also confirmed to be found in Brunei for the first time in 2022, in the country's Temburong District.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Prior to the discovery, it was believed that they may occur there and has been recorded c. Template:Convert from the border.<ref name="CITESprop">Template:Cite journal</ref> There are no records from Sabah, Central Kalimantan or South Kalimantan.<ref name=Langner2017/><ref name=CITESprop/>

It is found in lowlands at elevations below Template:Convert near streams and marshes.<ref name=Das2010>Template:Cite book</ref><ref name=Traffic2015>Template:Cite journal</ref> 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.<ref name=Yapp2012/><ref name=Langner2017/><ref name=Das2010/> The streams it inhabits are often rocky.<ref name=Yapp2012/><ref name=Langner2017/> Its habitat is tropical with air and water temperatures that generally are about Template:Convert,<ref name=Vergner2013/><ref name=Langner2017/> and captives reportedly prefer Template:Convert.<ref name=Pianka2004>Template:Cite book</ref> At a site with a high density of earless monitor lizards the water was clear and had a neutral pH.<ref name=Langner2017/> It is associated with the same microhabitat as Tropidophorus water skinks and in some places its range overlaps with T. brookei.<ref name=Langner2017/>

Appearance

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.<ref name=Das2010/><ref name=Pianka2006>Template:Cite book</ref> The species is extensively covered in osteoderms.<ref>Template:Cite journal</ref> Despite the name, they are capable of hearing, although lack a tympanum, an ear opening and other externally visible signs of ears.<ref name=EoR/><ref>Template:Cite journal</ref> The upperparts are orangish-brown, and the underside is mottled dark brown and whitish, pale yellowish, ochre or rusty.<ref name=Sprackland1999/><ref name=Yapp2012/><ref name=Das2010/> The tail is prehensile and if it is lost, it is not regenerated.<ref name=Pianka2006/> The skin is shed infrequently, possibly less than once a year.<ref name=Pianka2006/> There are both reports of the skin shedding in one piece (similar to snakes),<ref name=Pianka2006/> or in smaller pieces (as typical of lizards).<ref name=BTDescription>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Overall the sexes are alike, but males have a distinctly broader head and broader tail base than females.<ref name=Langner2017/> The differences between the sexes are clearly noticeable from an age of about three years.<ref name=BTGeschlechtsunterschiede>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> They sometimes oscillate the throat (similar to frogs) and the forked tongue is sometimes flicked (similar to snakes).<ref name=Langner2017/> They can make a gentle, squeaky vocalization.<ref name=Langner2017/>

Size

Adult earless monitor lizards typically have a snout-to-vent length (SVL) of about Template:Convert,<ref name=Das2010/> and a total length of about Template:Convert.<ref name=BTDescription/> Eighteen wild individuals, six males and twelve females, ranged from Template:Convert in SVL, Template:Convert in tail length (disregarding one individual missing much of its tail), and Template:Convert in weight (disregarding one sickly and skinny individual).<ref name=Langner2017/> Among these, the largest total length (SVL+tail) was a male that measured Template:Convert, which also is the longest recorded in the wild.<ref name=Langner2017/> A specimen collected in the 1960s has a total length of Template:Convert,<ref name=Sprackland1999/> and near the time of its death an individual kept at the Bronx Zoo from 1968 to 1976 had a total length of Template:Convert and weighed Template:Convert, but it was highly obese.<ref name=Mendyk2015>Template:Cite journal</ref> When hatching the total length of the young is about Template:Convert.<ref name=Vergner2013/><ref name=Shirawa2015>Template:Cite journal</ref><ref name=ViennaOnline2017>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> When one year old, their total length is about Template:Convert.<ref name=BTAufzucht>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>The Record size of earless monitor is 55 cm.<ref>https://muse.jhu.edu/pub/3/edited_volume/chapter/1930780</ref>

Behavior

Earless monitor lizards are generally strictly nocturnal animals, although exceptional daytime observations in the open have been reported.<ref name=Yapp2012/><ref name=Langner2017/> The day is usually spent near water in burrows that can be up to Template:Convert long or under logs, rocks or vegetation.<ref name=Das2013/><ref name=Das2010/> They are generally quite inactive and not agile, but can make surprisingly fast spurts when startled,<ref name=Langner2017/> and will rapidly catch prey items placed in front of them.<ref name=Shirawa2015/> 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.<ref name=Langner2017/> In captivity they sometimes remain virtually immobile underwater for hours, periodically lifting the nose above the water's surface to breathe.<ref name=BTVerhalten>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> When underwater, the semitransparent lower eyelids are generally closed, covering the eyes.<ref name=Langner2017/> It has been speculated that the prehensile tail is wrapped around stones, roots and other things underwater to avoid being swept along during floods.<ref name=Shirawa2015/>

Bite

Although generally docile and inactive when handled, males are usually more aggressive than females when caught.<ref name=Langner2017/> 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).<ref name=Langner2017/> This supported decades-old dissection studies where no venom glands or grooves in the teeth were found.<ref name=Sprackland1999/> 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,<ref name=Shirawa2015/> with blood clotting reportedly being slower than in normal wounds.<ref name=BTDescription/> Recent studies have found both venom glands,<ref>Template:Cite journal</ref> and toxic compounds in the bite of this species.<ref name=Koludarov2017>Template:Cite journal</ref> 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.<ref name=Koludarov2017/> 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.<ref name=Dobson2019>Template:Cite journal</ref>

Feeding

They typically feed on earthworms, crustaceans and fish.<ref name=Das2010/> 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.<ref name=Langner2017/><ref name=Mendyk2015/><ref name=ViennaOnline2017/><ref name=BTVerhalten/> In captivity adults typically eat once or twice per week, but sometimes enter longer periods where they do not feed.<ref name=BTVerhalten/> Unusually for a lizard, they can swallow prey while submerged underwater. The only other monitor species reported to do this is Mertens' water monitor.<ref name=Mendyk2015/> They appear to be able to do this by draining water from their nostrils, similar to turtles.<ref name=Shirawa2015/>

Breeding and life cycle

Like their closest relatives, they are oviparous, although little is known about their reproduction.<ref name=EoR/> Based on captive observations a pair will mate repeatedly over a period of a few months, with each session lasting for hours.<ref name=MReising>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In one case, a single mating lasted 44 hours.<ref name=Shirawa2015/> They mate in the water.<ref name=MReising/><ref name=BTPaarung>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> In the wild mating has been seen in February,<ref name=Das2013/> and a female caught in April was likely gravid.<ref name=Langner2017/> The 2–12 (average 8) oval eggs measure about Template:Convert long and have a leathery white shell.<ref name=Sprackland1999/><ref name=Das2010/><ref name=Shirawa2015/><ref name=BTEiablageInkubationSchlupf>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> They are deposited on land.<ref name=BTEiablageInkubationSchlupf/> In captivity the eggs hatch after about three months at a temperature of Template:Convert.<ref name=Shirawa2015/><ref name=ViennaOnline2017/> 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.<ref name=Langner2017/> 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.<ref name=BTVerhalten/> 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 Template:Convert in total length),<ref name=Mendyk2015/> and others have reportedly surpassed a decade in captivity.<ref name=Sprackland1999/>

Status and conservation

The earless monitor lizard has been rated by the IUCN as endangered (its range covers less than Template:Convert).<ref name=Traffic2015/> 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.<ref name=Sprackland1999/> Confirmation from Kalimantan only appeared later.<ref name=Langner2017/> 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.<ref name=Yapp2012/> At three other sites in the region the majority asked were aware of its presence, but less than half considered it common.<ref name=Yapp2012/> Elsewhere in West Kalimantan, a three-night survey of a Template:Convert 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.<ref name=Langner2017/> 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.<ref name=Langner2017/> Nevertheless, at present the earless monitor lizard is only known for certain from a relatively small number of sites.<ref name=CITESprop/><ref name=Traffic2015/>

About 100 museum specimens are known and most major natural history museums have one or more in their collection.<ref name=Sprackland1999/> These were generally collected in the 1960s–1980s or earlier,<ref name=Vergner2013/> often during floods when earless monitor lizards were swept along the current and ended up in fishing traps.<ref name=Sprackland1999/><ref name=Pianka2006/> From the 1960s to the 1990s small numbers entered the pet trade.<ref name=Mendyk2015/> In 2012 it was featured in a Japanese reptile keepers magazine and in the following years a larger number of individuals entered captivity.<ref name=CITESprop/><ref name=TodayOnline2016>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref name=Traffic2014>Template:Cite book</ref> 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.<ref name=Traffic2014/> 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).<ref name=Traffic2014/> 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.<ref name=Yapp2012/><ref name=Langner2017/> 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.<ref name=TodayOnline2016/> 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.<ref name=TodayOnline2016/> Significant declines in price have also been noted elsewhere.<ref name=Guardian2015>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Unlike all other monitor species, the earless monitor lizard was not listed on CITES, which would restrict trade at an international level.<ref name=TodayOnline2016/><ref name=Traffic2014/> In 2016 it was proposed that it should be placed on CITES Appendix I,<ref name=CITESprop/> and in 2017 it was afforded a level of protection when placed on Appendix II (export quota is zero for wild individuals for commercial purposes).<ref name=CITES2017>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

The first confirmed captive breeding was at a zoo in Japan in 2014.<ref name=Mendyk2015/><ref name=Shirawa2015/> 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.<ref name=ViennaOnline2017/><ref>Archived at GhostarchiveTemplate:Cbignore and the Wayback MachineTemplate:Cbignore: {{#invoke:citation/CS1|citation |CitationClass=web }}Template:Cbignore</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref> 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.<ref name=Traffic2015/>

Habitat loss represents another serious threat, as forests in Borneo rapidly are being replaced by oil palm plantations.<ref name=Langner2017/><ref name=Pianka2006/><ref name=TodayOnline2016/> 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.<ref name=Langner2017/>

External links

• Maisano, Jessie (2001). Lanthanotus borneensis. Digital Morphology. Accessed June 20, 2010.