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Holbrookia propinquaKeeled Earless Lizard

By Melissa Winchester

Geographic Range

This lizard species lives only in Southern Texas and coastal northeastern Mexico, as far south as Guanajuato. You won't find these unique lizards anywhere else (Behler and King 1979).

Habitat

Keeled earless lizards are endemic to barrier beaches and sand dumes. Some prefer to live closer to the coast than others, but all of them prefer to live in dry sandy places. There are unique adaptions that Keeled earless lizards have, that allows them to live on sandy habitats. For a small lizard, they have long legs and feet for getting around at relatively fast speeds on the sand. Their blotched coloring gives them the advantage of camouflage. Burrowing into sand to hide and regulate their temperature is made easier by the shape of their head. The sand dunes on Padre Island on the Texas coast is one place where there are many keeled earless lizards. (Behler and King 1979; Bechtel 1995)

Physical Description

These are small lizards that have no external ear opening, and have a tail that is longer than their head and body. They range from 11-14.1cm (4 1/2 to 5 9/16 in.) in length. Maximum head and body length is 7 cm (2 3/8 in.), so the tail can be about as long as 7.6 cm (3 in.). However, these lizards often lose part of their tails to predators, and can grow a new one, so tail length is not a good characteristic for identification. Unlike the other species of earless lizards (all genus Holbrookia), they have tiny keels on their dorsal scales. Their scales are granular, meaning they do not over lap and very small. The males and females have different and unique markings that are useful in telling them apart. The males have large black bands on either side of their stomach. The females are lighter in color and lack the black bands. Most of the males and females have irregular patterns of brown and grey stripes and blotches that cover their back and head (Conant 1958; Behler and King 1979).

Reproduction

Keeled earless lizards have femoral pores on each hind leg. There are on average 14-15, but they can have as many as 20. The femoral glands open into the dermal follicles. It is not known what they do exactly, but it is agreed that they are used for reproduction. Since they are diurnal, they have fairly good vision. They rely on their vision for courtship. They have very noticable sexual dimorphism. The male and female coloring is very important. The female coloring is controlled by hormones. When they change colors, it is a signal to males that they are ready to mate. Like most lizards, Keeled earless lizards are oviparous. Females have unique coloring when they are carrying eggs. They tend to be orange or pink. The female digs a burrow in which to deposit her eggs. After hatching, their young on average are 3.8 cm (1 1/2") long and have the same blotchy coloring as the adults (Cochran and Goin 1970; Conant 1958; Bechtel 1995; Cogger and Zweifel 1998).

Behavior

Keeled earless lizards spend most of their time alone. They are very solitary, except during their breeding season. During breeding time the males tend to get competitive with each other.

They communicate by bobbing their heads, and doing "push-ups". Head bobbing and "push-ups" can be very aggressive. This behavior lets seems to be used to mark territory.

A common misconception people have is mistaking the "push-ups" as the lizards' way of regulating their body temperature. Actually, most of the heat that is produced by the "push-ups" is dissipated through their unique skin. Keeled earless lizards regulate their body temperature by being diurnal. They come out during the day and bask in the sun or lay on the warm sand to raise their temperature. When night comes, and it gets colder, they burrow into the sand to get warm.

Lizards have special tails that can regenerate. This special and unique adaption gives them some protection from predators. If a predator grabs their tail, the lizard would not be unable to get away, their tail would just break off. After the tail is broke off by the predator it keeps the predators' attention by wiggling, which gives the lizard time to escape. When attacked by a predator Keeled earless lizards scurry away and burrow into the sand, using the head to wiggle its way underneath. After the attack the tail will eventually grow back.

(Bechtel 1995; Cogger and Zweifel 1998) (Bechtel, 1995; Cogger and Zweifel, 1998)

Food Habits

Keeled earless lizards are insectivorous, which means that they hunt down and eat insects. It is unknown which insects these lizards prefer. They seem to eat whatever they can get ahold of. They are diurnal, so they are only active and forage for food during the day and not at night. It may get too cold for them at night, as they are cold blooded animals (Cochran and Goin 1970; Behler and King 1979). (Behler and King, 1979; Cochran and Goin, 1970)

Economic Importance for Humans: Positive

These lizards may benefit humans by helping control insect populations (Behler and King 1979).

Economic Importance for Humans: Negative

Unknown

Conservation Status

Keeled earless lizards are endemic to southern Texas and coastal Mexico, which means that they are found no where else. So if anything happens to their habitat they could become endangered or even worse, extinct.

Contributors

Melissa Winchester (author), Fresno City College, Jerry Kirkhart (editor), Fresno City College.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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carnivore

an animal that mainly eats meat

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

diurnal
  1. active during the day, 2. lasting for one day.
insectivore

An animal that eats mainly insects or spiders.

native range

the area in which the animal is naturally found, the region in which it is endemic.

References

Bechtel, B. 1995. Reptile and Amphibian Variants Colors, Patterns, and Scales. United States of America: Krieger Publishing Company.

Behler, J., F. King. 1979. Audubon Society Field Guide to North American Reptiles & Amphibians. United States: Alfred A. Knopf, Inc..

Bockstanz, L., D. Cannatella. 1999. "Herps of Texas: Holbrookia propinqua" (On-line). Accessed 4 April 2001 at http://www.zo.utexas.edu/research/txherps/lizards/holbrookia.propinqua.html.

Cochran, D., C. Goin. 1970. The New Field Book of Reptiles and Amphibians. United States: G.P. Putnam's Sons, New York.

Cogger, D., D. Zweifel. 1998. Encyclopedia of Reptiles & Amphibians. United States: Academic Press, A Division of Harcourt Brace & Company.

Conant, R. 1958. The Peterson Field Guide Series, A Field Guide to Reptiles and Amphibians of Eastern North America. Boston, MA, United States: Houghton Mifflin Company.

Hickman, C., L. Roberts, A. Larson. 2001,1997. Integrated Principles of Zoology. Eleventh Edition. New York: McGraw-Hill Companies, Inc..

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