Dumérils monitor lizard
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Duméril's monitor lizard ( Varanus dumerilii ) |
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| Varanus dumerilii | ||||||||||||
| Schlegel , 1839 |
Duméril's monitor lizard ( Varanus dumerilii ) is a species of lizard from Southeast Asia that has not been very well researched . Originally it was known as a tree-dwelling insect eater, today the image of the Dumérils Waran is characterized by an amphibious way of life and a food spectrum consisting mainly of crabs .
morphology
Dumérils Waran is a maximum of 1.30 meters long and weighs about one kilogram. The oar tail, which is compressed at the side, is 1.3 to 1.6 times as long as the head and torso. Dumérils Waran has a broad and flat skull with blunt teeth. The nostrils are slit-shaped and lockable, the latter is unique in monitor lizards. Duméril's monitor lizards can close the nasal passage flat by pushing the front of the relatively elastic skin flake forward. It is not possible to open this closure with tweezers without injuring the animal. The nostrils are closed for diving. Both sexes have distinctive preanal pores. Adult Dumérils monitor lizards are brown and drawn with cream-colored dorsal and cranial horizontal bands. Young animals are black, but the bandages are yellow to vermilion, but mostly in orange tones. The head of young animals has a similar color to the ribbon drawing. Except for the difference that males are slightly larger than females, the Dumérils Waran has no sexual dimorphism . The neck area of Duméril's monitor lizards has large scales.
Occurrence
Occurrences of Duméril's monitor lizard are known from Thailand , Burma , the Malay Peninsula , Borneo , Sumatra and many small islands. Dumérils monitor lizard lives mostly in coastal mangrove forests or damp inland forests, less often on agricultural land.
Way of life
General
The Duméril monitor lizard is diurnal and can swim and climb well. For a long time they were considered to be tree-dwelling, but apparently they live more amphibious. Sometimes they even swim in the sea, for example on the run. Apparently they sometimes stop in earthworks.
nutrition
For a long time the Duméril monitor lizard was considered an insect eater, which occasionally also eats eggs and birds. Ants, mice, eggs and entrails of chickens have been eaten in captivity. Conjectures are based on different diets in nature: the conjectures range from turtle eggs and ants to birds and insects.
However, recent research suggests crab food. Two dissected animals together contained a spider, an insect larva, and five crabs.
The ethologist Uwe Krebs carried out further investigations around 1979, which confirmed the result of the dissections. It has been observed, for example, that the Duméril monitor lizard has difficulty preying on vertebrates. For example, a mouse was grabbed centrally and not by the head; it often lies across its mouth. They also use their forelegs as an aid, but strangely enough in such a way that this makes it difficult for them to swallow, the prey is more likely to be moved out of the mouth. When the monitor lizards observed in captivity were served with crabs, they were able to cope with them much better than the mice, although the monitor lizards never had crabs in captivity. Central packing of the prey is ideal for crabs; The monitor lizard applied the same principle to the mouse. In crabs, the movement of the front legs has the purpose of slipping off the claws clinging to the waran head. In the case of larger species, the scissors are sometimes pried off before the actual feeding act, sometimes even all legs with the scissors. In the case of large crabs, the act of swallowing is supported by prying them against a solid surface, since a lot of force is required to swallow the large crabs. Furthermore, there are additional adjustments to the crab food: The flat skull, for example, can very easily penetrate the narrow crevices where the rather flat crabs often stay.
Reproduction
The only data on the reproduction of the Duméril monitor lizard come from captive animals. The nests contain up to 23 eggs, a female can lay eggs three times a year. The eggs are three centimeters long and usually weigh more than 34 grams. At temperatures of 29 ° C, the young hatch after 203 to 234 days. Hatchlings are 21 centimeters long and weigh eleven grams.
Systematics
The traditional classification follows the model of Robert Mertens , which he published in a large Waran monograph from 1942. He is the only representative of her in the monotypical subgenus Tectovaranus . Mertens justified this classification with the construction of the skull of the Duméril monitor lizard: This is quite heavy for monitor lizards, and is short, wide and flat. In addition, it is striking that the juvenile stages of monitor lizards are usually built in a generalist manner and only take on the specialized forms in old age, but with the Duméril monitor lizard this special skull shape is already present in young animals. In addition, the small size of the skull in relation to the body is assessed as a distinguishing feature. It is questionable whether the Duméril monitor lizard is a phylogenetically old or a young type. Since only younger species are highly specialized and, like the Duméril dragon, have a slit-shaped nostril, the Duméril dragon is obviously a young type. An examination of the structure of the Hemipenes, however, came to different results. According to her, the Duméril monitor lizard should be classified together with Varanus bengalensis , Varanus rudicollis and Varanus flavescens in the subgenus Empagusia . According to the system used here (Ziegler & Böhme 1997 and Böhme 2003), these species are to be classified in the same subgenus.
There are no known fossils of Varanus dumerilii .
The species was first mentioned by Hermann Schlegel as Monitor dumerilii , the type region of the Duméril monitor lizard is part of Borneo. Schlegel honored the French zoologist André Marie Constant Duméril with the specific epithet .
There are two geographical subspecies of the Duméril monitor lizard:
- Varanus dumerilii heteropholis - inhabits the north and east of Borneo
- Varanus dumerilii dumerilii (nominate form) - inhabits the rest of the distribution area.
swell
literature
- Daniel Bennet: Varanus dumerilii . In: Eric Pianka & Dennis King (Eds.): Varanoid Lizards of the World . Indiana University Press, published 2004; Pp. 172-175. ISBN 0-253-34366-6
- Uwe Krebs: The Duméril monitor lizard (Varanus dumerilii), a specialized crab eater? Salamandra 15, 146-157 (1979)
- Maren Gaulke : On the biology of the water monitor, taking into account the palaeogeographic distribution and the phylogenetic development of the Varanidae , Senckenbergische Naturforschende Gesellschaft Frankfurt a. M., Frankfurt am Main June 30, 1989, ISBN 3-924500-49-5
- Manfred Rogner: Echsen 2 , Eugen Ulmer, 1999, ISBN 3-8001-7253-4
- Jiri Rotter: Die Warane , Die Neue Brehm Bücherei Volume 325, Westarp Sciences, ISBN 3-89432-466-X
Footnotes
- ↑ According to Schmidt & Inger (1957), quoted in Rotter (new edition from 1963)
- ^ After Barbour (1921), cited in Krebs (1979)
- ^ Based on Mitsch (1936) and Ladiges (1939), cited in Krebs (1979)
- ↑ After Raven (1946), quoted in Pianka & King (2004)
- ↑ After Barbour (1921), quoted in Pianka & King (2004)
- ↑ After Pitman (1962), cited in Pianka & King (2004)
- ^ Based on Auffenberg (1988), quoted in Pianka & King (2004)
- ↑ After Losos & Greene (1988), cited in Pianka & King (2004)
- ↑ According to Mertens (1942), cited in Krebs (1979)
- ↑ After Böhme, quoted in Gaulke (1989)
