Earless monitor lizard
The earless monitor lizard (Lanthanotus borneensis) is a semi-aquatic, 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.
The earless monitor lizard was described in 1878 by Franz Steindachner. 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 recognized from the start 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. Further studies were conduced in the 1950s where it was found that although it was related to Helodermatidae, this relationship was relatively distant 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 the true monitor lizards in Varanoidea, but more recent genetic evidence has found that the earless monitor lizard and true monitor lizards form a clade, and these two and Shinisauridae are sister to Helodermatidae. The most recent common ancestor diverged in the mid-Cretaceous.
Range and habitat
The earless monitor lizard is endemic from the Southeast Asian island of Borneo. Here it is known from Sarawak in East Malaysia, as well as West and North Kalimantan in Indonesia. Until late 2012, its known range in North Kalimantan was a part of East Kalimantan. It is not known from Brunei, but may occur there and has been recorded c. 100 km (60 mi) from the border. There are no records from Sabah, Central Kalimantan or South Kalimantan. The species is easily overlooked.
It is found in tropical lowlands at altitudes below 300 m (980 ft) near streams and marshes. These are typically in rainforests, but it is also found in streams flowing through degraded habitats such as agricultural land and palm oil plantations, and reportedly may occur in rice paddies. The streams it inhabits are often rocky. It is associated with the same microhabitat as Tropidophorus water skinks and in some places its range overlaps with T. brookei.
Earless monitor lizards have a cylindrical body, long neck, short limbs, long sharp claws, small eyes, semitransparent lower eyelids, and six longitudal rows of strongly keeled scales. Despite the name, they are capable of hearing, although lack a tympanum, an ear opening and other externally visible signs of ears. The upperparts are orangish-brown, and the underside is mottled with pale yellowish, ochre or rusty. The tail is prehensile and if it is lost, it is not regenerated. The skin is shed infrequently, possibly less than once a year, and in one pierce, similar to snakes. Overall the sexes are alike, but males have a distinctly broader head and broader tail base than females. They sometimes oscillate the throat (similar to frogs) and the forked tongue is sometimes flicked. They can make a gentle, squeaky vocalization.
Earless monitor lizards typically have a snout-to-vent (SVL) length of about 20 cm (8 in). 18 wild individuals, 6 males and 12 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. A specimen collected in the 1960s had a total length of 51 cm (20 in), 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 (19 in) and weighed 209.3 g (7.38 oz), but it was highly obese. When hatching the total length of the young is about 7–10 cm (3–4 in).
Earless monitor lizards are generally strictly nocturnal animals, although exceptionally daytime observations in the open have been reported. The day is usually spend near water in burrows that can be up to 30 cm (1 ft) long or under logs, rocks or vegetation. They are generally quite inactive and not agile, but can make surprisingly fast spurts when startled. 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.
They typically feed on earthworms, crustaceans and fish. In captivity, they will eat squid, pieces of fish, earthworms, tadpoles, yolk from green sea turtle eggs, and pieces of pig and chicken liver, but refuse to take bird eggs, legs of frog and feet of mussels. Unusually for a lizard, they can swallow prey while submerged underwater. When submerged, the semitransparent lower eyelids are generally closed.
Like their closest relatives, they are oviparous, although little is known about their reproduction. Based on captive observations a pair will mate repeatedly over a period of a few months, with each session lasting for hours. In the wild mating has been seen in February, and a female caught in April was likely gravid. The 2–5 oval eggs measure about 3 cm (1.2 in) and have a leathery shell. In captivity the eggs hatch after three months. Males are likely territorially aggressive, as a study 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. Captives have been kept together without problems, but it is unclear if this involved multiple males. Although generally docile and inactive when handled, males are usually also more aggressive than females when caught, and in one case a scientist received a deep bite in his finger. Unlike their relatives (beaded lizards, gila monster and some monitor lizards), there were no indication of venom in the bite, supporting earlier dissection studies where no venom glands or grooves in the teeth were found. The lifespan is unknown, but—despite the very limited knowledge of reptile keeping at the time—individuals that entered captivity as young adults in the 1960s lived for up to 7.5 years after capture.
Status and conservation
The earless monitor lizard has not been rated by the IUCN, but it likely qualifies for vulnerable (if its range covers less than 2,000 km2 or 770 sq mi) or endangered (if its range covers less than 500 km2 or 190 sq mi). 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. Confirmation from Kalimantan only appeared later. 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. Elsewhere in West Kalimantan, a three-night survey of a 400 m (1,300 ft) long section of a stream 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. Nevertheless, at present the earless monitor lizard is only known for certain from a relatively small number of sites.
About 100 museum specimens are known and most major natural history museums have one or more in their collection. These were generally collected in the 1960s–1980s or earlier, often during floods when earless monitor lizards were swept along the current and ended up in fishing traps. In 2012 it was featured in a Japanese reptile keepers magazine, and shortly after individuals started appearing in the pet trade (smaller numbers had appeared earlier). From May 2014 to October 2015 at least 95 earless monitor lizards entered 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. 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). 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. 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. Significant declines in price have also been noted elsewhere. Unlike all other monitor species, the earless monitor lizard was not listed on CITES, which would restrict trade at an international level. In 2016 it was proposed that it should be placed on Appendix I, and this was adopted in 2017.
The first confirmed captive breeding was at a zoo in Japan in 2014, and in 2016–2017 it was bred at Schönbrunn Zoo in Austria. There have been other breeding reports by private keepers and captive bred individuals have been offered for sale, but at least some of these may not involve genuine cases of captive breeding.
Habitat loss represents another serious threat, as forests in Borneo rapidly are being replaced by oil palm plantations. 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.
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