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Earless monitor lizard
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 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 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. More recent genetic evidence has found that the nearest relative of the earless monitor lizard is Varanidae. Most authorities continue to recognize them as separate families as the divergence between them is deep, but some have suggested that the earless monitor lizard should be included as a subfamily, Lanthanotinae, of the Varanidae. 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. The most recent common ancestor diverged in the mid-Cretaceous.
The extinct Cherminotus known from Late Cretaceous fossil remains in Mongolia has been considered a member of Lanthanotidae, but this is disputed.
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. Until late 2012, its known range in North Kalimantan was a part of East Kalimantan. It was also confirmed to be found in Brunei for the first time in 2022, in the country's Temburong District. Prior to the discovery, it was believed that they 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.
It is found in lowlands at elevations below 300 m (1,000 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, mature fruit tree gardens and palm oil plantations, and reportedly may occur in rice paddies. The streams it inhabits are often rocky. Its habitat is tropical with air and water temperatures that generally are about 22–29 °C (72–84 °F), and captives reportedly prefer 24–28 °C (75–82 °F). 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.
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. The species is extensively covered in osteoderms. 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 dark brown and whitish, 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. There are both reports of the skin shedding in one piece (similar to snakes), or in smaller pieces (as typical of lizards). Overall the sexes are alike, but males have a distinctly broader head and broader tail base than females. The differences between the sexes are clearly noticeable from an age of about three years. 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.
Adult earless monitor lizards typically have a snout-to-vent length (SVL) of about 20 cm (8 in), and a total length of about 40 cm (16 in). 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. A specimen collected in the 1960s has 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 (18.5 in) and weighed 209 g (7.4 oz), but it was highly obese. When hatching the total length of the young is about 7–14 cm (3–6 in). When one year old, their total length is about 23–25 cm (9–10 in). The record size of earless monitor is 55 cm.
Earless monitor lizards are generally strictly nocturnal animals, although exceptional daytime observations in the open have been reported. 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. They are generally quite inactive and not agile, but can make surprisingly fast spurts when startled, and will rapidly catch prey items placed in front of them. 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. In captivity they sometimes remain virtually immobile underwater for hours, periodically lifting the nose above the water's surface to breathe. When underwater, the semitransparent lower eyelids are generally closed, covering the eyes. It has been speculated that the prehensile tail is wrapped around stones, roots and other things underwater to avoid being swept along during floods.
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Earless monitor lizard
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 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 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. More recent genetic evidence has found that the nearest relative of the earless monitor lizard is Varanidae. Most authorities continue to recognize them as separate families as the divergence between them is deep, but some have suggested that the earless monitor lizard should be included as a subfamily, Lanthanotinae, of the Varanidae. 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. The most recent common ancestor diverged in the mid-Cretaceous.
The extinct Cherminotus known from Late Cretaceous fossil remains in Mongolia has been considered a member of Lanthanotidae, but this is disputed.
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. Until late 2012, its known range in North Kalimantan was a part of East Kalimantan. It was also confirmed to be found in Brunei for the first time in 2022, in the country's Temburong District. Prior to the discovery, it was believed that they 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.
It is found in lowlands at elevations below 300 m (1,000 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, mature fruit tree gardens and palm oil plantations, and reportedly may occur in rice paddies. The streams it inhabits are often rocky. Its habitat is tropical with air and water temperatures that generally are about 22–29 °C (72–84 °F), and captives reportedly prefer 24–28 °C (75–82 °F). 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.
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. The species is extensively covered in osteoderms. 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 dark brown and whitish, 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. There are both reports of the skin shedding in one piece (similar to snakes), or in smaller pieces (as typical of lizards). Overall the sexes are alike, but males have a distinctly broader head and broader tail base than females. The differences between the sexes are clearly noticeable from an age of about three years. 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.
Adult earless monitor lizards typically have a snout-to-vent length (SVL) of about 20 cm (8 in), and a total length of about 40 cm (16 in). 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. A specimen collected in the 1960s has 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 (18.5 in) and weighed 209 g (7.4 oz), but it was highly obese. When hatching the total length of the young is about 7–14 cm (3–6 in). When one year old, their total length is about 23–25 cm (9–10 in). The record size of earless monitor is 55 cm.
Earless monitor lizards are generally strictly nocturnal animals, although exceptional daytime observations in the open have been reported. 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. They are generally quite inactive and not agile, but can make surprisingly fast spurts when startled, and will rapidly catch prey items placed in front of them. 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. In captivity they sometimes remain virtually immobile underwater for hours, periodically lifting the nose above the water's surface to breathe. When underwater, the semitransparent lower eyelids are generally closed, covering the eyes. It has been speculated that the prehensile tail is wrapped around stones, roots and other things underwater to avoid being swept along during floods.