Short-horned toad lizard
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Short-horned toad lizard ( Phrynosoma douglasii ) |
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Short-horned toad lizards is / are one ( Phrynosoma douglasii ) or, depending on the opinion, two (then also Phrynosoma hernandesi ) representatives of the toad lizards from the genus Phrynosoma up to 15 centimeters long . About the status of an earlier than subspecies Phrynosoma douglasii hernandesi guided Great Shorthorn horned toad , sometimes for new knowledge as a separate species Phrynosoma hernandesi is considered, there is still disagreement.
The lizards live in rocky and sandy dry areas or sparse forests in large parts of the western USA as well as in southern Canada and northern Mexico .
Appearance
Like other Phrynosoma species, the short-horned toad lizard has a flattened, broad body and a very short, blunt, broad-mouthed snout, which is reminiscent of the appearance of a toad . In addition, the tail and extremities are relatively short. The animals reach a total length of six to fifteen, but on average about seven to eight centimeters; the males are significantly smaller than the females. The weight averages about 20 grams for the latter and twelve grams for the former. The entire body is covered by spines that look like small horns on the head. Compared to the desert toad lizard ( Phrynosoma platyrhinos ) that occurs in the same habitat , these are, as their German name suggests, quite small. The tail is also surrounded by a row of thorny scales, while the scales of the throat are smooth.
The color varies between gray, yellowish or reddish brown shades; on the back there are two rows of dark spots. Often the most common color is very similar to the substrate. The ventral side is white to cream yellow. The mountain subspecies Phrynosoma douglasii hernandesi , which can be found in the high altitudes of Utah , Colorado , Arizona , New Mexico and Mexico , is largely reddish in color and has clear, horizontal spines on the flanks.
Way of life
Due to their short legs, short-horned toad lizards move very slowly. They feed on insects , especially ants . They can only recognize animals that are actively moving. Aside from insects, they also hunt snails and sometimes even small snakes . Despite this "alternative food", toad lizards are regarded as specialized ant-eaters (myrmetophage). In adaptation to the very chitin-rich ant diet, they have an enlarged stomach.
Short-horned toad lizards themselves are hunted by coyotes , foxes , falcons , ravens , snakes and, above all, larger species of lizards . In order to assert themselves against enemies, the lizards camouflage and hide, try to escape and in extreme cases also attack. The prickly body and the coloring as well as the very slow movement offer an excellent camouflage. The spines also convey a larger appearance and thus deter potential predators. In order to intensify this effect, the animals also open their mouths during attacks.
The main activity of the lizards takes place during the day, while they burrow at night. The short-horned toad lizard is very cold-tolerant compared to all other toad lizards, which is why it can be found at altitudes of up to 2,700 meters. This is mainly due to the relatively small size and the dark color of the animals. It enables the body to be heated up to "operating temperature" very quickly in the sun. The animals have their maximum activity between 26 and 40 degrees Celsius body temperature, longer periods of time at temperatures above 41 degrees are fatal. In order to be able to dig in, however, they need at least partially frost-free soil outside of winter. They survive the winter by digging themselves about seven to ten centimeters deep into the ground and falling into a frozen state there. Depending on the temperatures, this lasts from late September to the beginning of May, but if the outside temperatures are appropriate, they can still become active and dig themselves out in October or November.
Reproduction
Mating takes place between April and July, and the males actively search for a female. Rival fights for a selected partner occur relatively often among them. During pregnancy, the female can double her weight, each of the young weighs about one gram shortly before birth. They are born alive between July and August ( ovoviviparic ), a litter consists of six to thirty individuals. The mother first builds a nest of plant material in which she lays the newborns.
The approximately 22 millimeter long young animals can take care of themselves within a few hours, but the typical spines and horns only grow much later. Their mortality , especially from predators, is very high, which is why only a few of the relatively large number of animals survive. In contrast, the survival rate of the adult animals is very high. The males are fully grown after about one year, the females after two years, both have a lifespan of about five years.
Systematics
The short-horned toad lizard is generally regarded as a species of toad lizard, but recent studies from 1997 (Zamudio et al. 1997) led to the finding that it could be a collective taxon of two separate species. These were named as:
- Little short-horned toad lizard ( Phrynosoma douglasii ) (Bell 1829) or
- Great short-horned lizard ( Phrynosoma hernandesi ) (Girard 1858), also known as the mountain short-horned lizard.
The latter is the former subspecies Phrynosoma douglasii hernandesi , which is regarded as a new species .
All other groups previously regarded as subspecies of Phrynosoma douglasii ( P. d. Brevirostre , P. d. Ornatum , and P. d. Ornatissimumals ) were also characterized as synonyms for Phrynosoma hernandesi . The dwarf short-horned toad lizard therefore only occurs in the Columbia River area.
If one proceeds from the conservative point of view that the short-horned toad lizard is still a species, then within the toad lizard it is likely to be related to the Mexican short-horned toad lizard ( Phrynosoma orbiculare ). This was confirmed by Reeder & Montanucci in 2001 on the basis of anatomical and molecular features:
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According to Montanucci 1987, it forms a monophylum together with the rock toad lizard ( Phrynosoma ditmarsi ) and the Mexican short-horned toad lizard ( Phrynosoma orbiculare ) . According to Zamudio et al. 1997, however, who advocates a split of the species, the sister species of the dwarf short-horned toad lizard is the rock- toed lizard ( Phrynosoma ditmarsi ), so that the representatives of the short-horned toad lizard themselves no longer form a natural group - this is accordingly used as an argument for the split used in two ways.
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Threat and protection
The populations and numbers of toad lizards are declining, mainly due to the loss of their habitat and wild catches for the terrarium sector . For this reason, the trade was subject to various regulations, the collection of wild animals is prohibited or restricted by law outside of the national parks in some states, first in Texas in 1967. The toad lizards are extremely well adapted to their habitat, and they are correspondingly sensitive to changes in their environment. Outside of their habitat , the animals often die very quickly. Before the animals were placed under protection, hundreds of thousands of toad lizards were exported alive or dead by tourists and traders every year. Especially in Nevada and Mexico , trading and fishing is still allowed today.
The loss of habitat is mostly directly related to the settlement of the habitats with people. Planted lawns and pastures make it difficult for the toad lizards to camouflage or bury themselves, and there is a higher feeding pressure from the settlers' domestic animals, especially dogs and cats.
Another danger for the animals is the introduced red fire ant ( Solenopsis invicta ), which attacks all small animals in their habitat and can kill them due to the large number of individuals. Since the toad lizards feed primarily on ants, they are directly exposed to the threat of the defensive neozoa .
Terrariums
All toad lizards are popular terrarium animals in North America and Western Europe because of their appearance, although the short-horned toad lizard is kept less frequently than other species. However, keeping and breeding the animals is very difficult. Although it is now possible to breed almost all toad lizard species , these are quite complex. The majority of the toad lizards available in the trade are accordingly wild-caught. With the exception of the Texas toad lizard, for which possession must be legitimized by CITES papers according to the EU species protection regulation , there are no keeping restrictions for the phrynosoma species in Europe .
The toad lizards are not suitable as beginner animals. When equipping the terrarium, the special requirements of the animals must be taken into account. During the day, the animals need temperatures of around 30 degrees Celsius, a ground cover made of sand and earth in which the animals can burrow, a tanning area with an installed heater, and food that consists to a large extent of ants.
etymology
The scientific name of the species Phrynosoma douglasii is derived from the term Phrynosoma , "toad body", which refers to the toad-like shape and was proposed by Wiegmann as early as 1828 , as well as by a herpetologist named David Douglass , who worked in the area in the early 19th century of the Columbia River. The "new" species Phrynosoma hernandesi , first named in 1858 by Charles Frédéric Girard and later seen as a synonym for P. douglasii , is named after Francisco Hernandez , a Spanish medic and botanist.
literature
- Bertrand Baur, Richard R. Montanucci: Toad lizards . Way of life, care, breeding. Herpeton, Offenbach 1998, ISBN 3-9802892-8-1 .
- John L. Behler, F. Wayne King: The Audubon Society Field Guide to North American Reptiles and Amphibians. Alfred A. Knopf, New York NY 1979, ISBN 0-394-50824-6 .
- James E. Heath: Temperature regulation and diurnal activity in horned lizards. In: University of California Publications in Zoology. Vol. 64, No. 3, 1965, ISSN 0068-6506 , pp. 97-136.
- Richard R. Montanucci: A phylogenetic study of the horned lizards, genus Phrynosoma, based on skeletal and external morphology (= Contributions in Science. No. 390, ISSN 0459-8113 ). Natural History Museum of Los Angeles County, Los Angeles CA 1987, digitized version (PDF; 4.8 MB) .
- Eric R. Pianka, William S. Parker: Ecology of Horned Lizards: A Review with Special Reference to Phrynosoma platyrhinos. In: Copeia. Vol. 1975, No. 1, 1975, pp. 141-162, doi : 10.2307 / 1442418 .
- Tod W. Reeder, Richard R. Montanucci, John D. McEachran: Phylogenetic analysis of the horned lizards (Phrynosomatidae: Phrynosoma). Evidence from mitochondrial DNA and morphology. In: Copeia. Vol. 2001, No. 2, 2001, pp. 309-323, doi : 10.1643 / 0045-8511 (2001) 001 [0309: PAOTHL] 2.0.CO; 2 .
- Wade C. Sherbrooke: Collecting and feeding harvester ants to captive horned lizards. In: Herpetological Review. Vol. 26, No. 1, 1995, ISSN 0018-084X , pp. 25-26.
- Kelly R. Zamudio, K. Bruce Jones, Ryk H. Ward: Molecular systematics of short-horned lizards. Biogeography and taxonomy of a widespread species complex. In: Systematic Biology. Vol. 46, No. 2, 1997, pp. 284-305, doi : 10.1093 / sysbio / 46.2.284 .
Web links
- Phrynosoma douglasii in The Reptile Database
- Phrynosoma.ch
- Horned Lizards (English)
- The Horned Lizard Conservation Society (English)
