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Crosstimbers Connection Connecting People with Nature in North Texas


Reptiles are vertebrates (they have backbones) and cannot generate their own body heat (they are “cold-blooded”). They possess skin with scales, and with a few exceptions they lay shelled eggs. When hatched or born, they do not go through a larval stage like the amphibians. Traditionally, reptiles have included the turtles, lizards, snakes, crocodilians, and the tuatara of New Zealand. Texas has 210 “kinds” of reptiles (counting species and subspecies), according to the second edition of Dixon’s Amphibians and Reptiles of Texas.

Turtles are reptiles that have, to one degree or another, evolved their own personal armor - a bony shell covering them above and below. The top shell is called the “carapace” and is composed of fused ribs and plates made of bone, covered by living tissue. For most turtles, that covering is a series of “scutes” made of the same sort of tissue found in our fingernails. The bottom shell is the “plastron” which is a sort of bony extension of the breastbone, also covered with scutes.

The earliest turtles appeared before the dinosaurs, so they have carried those shells around for a very long time! Another way of thinking of this is that the shell has worked really well for them. Some turtles have relatively small shells - for example the snapping turtle has a large head, long neck, and long tail that extends way past the edge of the shell. The snapper’s plastron is very small, giving its underside little protection. Of course, with such strong jaws, perhaps it doesn’t need much protection on its belly.

 Even the snapping turtle can pull its head completely within its shell. How does it do this? Turtles have backbones and neck bones just like other vertebrates, so unless its neck is like an accordion, how does it pull its head in? Most turtles (and all of them in North America) do this by bending the neck in a vertical S-curve so that the head is pulled in under the curves of the neck. This all happens within the body, so we cannot see that S-curve of the spine by watching the turtle. All we see is the head retract in. A smaller group of turtles in a few places in the world pull their heads in by folding their necks to the side (and are called “side-necked turtles”).  

Turtles have no teeth, but they have beaks that may be sharp and jaw muscles that often are very strong. Some of our turtles eat snails, which requires strong jaws to crunch through the shells. Some turtles, like the Texas tortoise, are vegetarian. Others may eat mollusks, insects, and carrion. Still other turtles have a diet that includes vegetables, fruit, as well as insects, earthworms, and other items.

Texas is home to many turtle species, including several sea turtles along the Texas coast, and freshwater turtles such as the softshell turtles, snapping turtles, sliders and cooters. Our box turtles are primarily “land turtles,” and the Texas tortoise is a land turtle found in south Texas that is protected and cannot be collected. See the Texas Turtles website for more details about the various species.

Even the strongest shell cannot protect turtles from being run over by cars, losing their homes when wild places are developed, or being collected by people for food or pets. The year 2011 was declared the “Year of the Turtle” by turtle conservation groups and Partners in Amphibian and Reptile Conservation. One way we can help is by not collecting turtles from the wild or buying turtles that have been taken from the wild.

 In fact, we’re probably better off watching wild turtles than trying to keep them as pets. Most turtles require regular exposure to direct sunlight (or some source of ultraviolet-B) to stay healthy, and they may have special dietary needs. The best captive arrangement for most turtles is an outdoor setup with access to water, shade and sun, shelter, and protection from predators such as raccoons.

Lizards are reptiles that generally have four legs, eyelids and external ear openings (though there are some exceptions). Their bodies are covered with scales; in some, the scales are rather large, while in others they are tiny and granular. Some have very smooth and glossy scales. Others have some of the scales modified into spines or horns.

A great many of the smaller lizard species eat insects and other invertebrates, but there are also species that are mostly vegetarian. A few lizards have very specialized diets, such as the horned lizards that eat mostly ants. (Unfortunately, they do not eat the red imported fire ants!)

Lizards have developed some of the most bizarre bodies in the reptile world. The frilled dragon of Australia has large folds of skin that open like an umbrella around its face to startle an enemy. The true chameleons have tongues that can project out, much longer than their whole body, to stick onto an insect and pull it back to their mouths. A few species, such as the glass lizards, have evolved long bodies without legs. However, they are not snakes; their head structure remains lizard-like, with eyelids, external ears, and lacking the snake’s modified jaw structures.

Texas has many lizard species that live in the deserts, the mountains of the Big Bend, the coastal plains, the piney woods, the prairies, and everywhere else. Some, such as the whiptails, live on the ground and are extremely fast. Others, such as the alligator lizard, live mostly in trees or shrubs and are not particularly fast. The Texas State Reptile is the Texas horned lizard, which is the "horny toad" that used to be common but has now disappeared from much of the state. A really good DVD that explores this problem is "Where Did the Horny Toad Go?" available from Jar of Grasshoppers Productions.

A good way to get to know our lizards is to watch from just far enough away that the little reptile does not make a quick getaway. Lizard-watching can be done through binoculars or a camera’s zoom lens for details. One reason not to try to catch them for a close look is that many lizards’ tails are easily broken off. In fact, the muscles and bones of some lizard tails are designed to easily break and then heal with little bleeding. Why would this be? The answer is that many birds, reptiles, and other animals eat lizards, and if they grab the tail the lizard may escape with its life by losing its tail. A new tail will grow from the stump, but usually it is shorter and is different in texture and color from the original tail.

Snakes are legless reptiles that have no external ears and eyes covered with a clear scale so that they cannot close their eyes. Their skin is covered with dry scales (they are not slimy!) and they have backbones with a large number of vertebrae that allow them to bend very flexibly. Most of them have small teeth and, if they bite, the result is only some minor scratches. Some species have evolved enlarged teeth (fangs) and can inject venom.

How do you get around if you have no legs? Snakes have developed several ways of moving about, and they can swim, climb, and crawl through very narrow spaces. They get around better and more gracefully than many animals that do have legs! The commonest method is called “serpentine” motion, and it involves the S-curve position of the body as the snake pushes against any irregularities on the ground with each curve of the body, pushing the snake forward. Some snakes use “rectilinear” movement, where muscles in various places along the belly tighten, push backward, then relax and move forward, pushing the snake forward like a caterpillar. Large boas and pythons often use this method, as do our rattlesnakes, copperheads, and cottonmouths. Such a snake may use rectilinear movement when stalking prey, but if danger threatens, they are capable of switching to the faster serpentine movement. Two other methods are “concertina” movement and “sidewinding.”

How do you eat when you have no arms or hands? You cannot pull off pieces or use a knife and fork! All snakes eat other animals (no veggies) and they have to eat the animal whole! A snake’s jaws are not just a simple one-hinged arrangement. Instead, the lower jaws connect with a quadrate bone that then attaches to the skull - giving two hinges for a greater range of movement. Also, the lower jaws connect at the front by a flexible ligament, so the lower part of the mouth can expand quite a bit. The muscles on each side of the head can move the jaws on one side outward and forward, while the jaws on the other side anchor the prey in the mouth. The jaws that moved forward now bite down and pull back, drawing the prey further into the mouth, while the other side reaches forward to get a new grip. The prey is gradually pulled into the mouth and down the throat.

The venomous snakes found in Texas fall into several groups: the copperheads (three kinds or “subspecies”), the western cottonmouth, the rattlesnakes (several species ranging from the very small pygmy rattlesnake to the much larger western diamond-backed rattlesnake), and the coral snake. The great majority of Texas snakes are harmless.

Crocodilians include alligators, crocodiles, and other animals such as caimans and gharials. All of these are large reptiles that live in and around water and are powerful swimmers. The U.S. has one crocodile species (confined, in the U.S., to south Florida) and one alligator species found from coastal North Carolina southward through Florida and west along the gulf coast through eastern and coastal Texas.

Alligators and crocodiles are very well adapted to life in the water. Not only do the ears and nostrils have flaps that can close when underwater, there is even a valve at the back of the mouth to keep the water out of the throat even when the mouth is open underwater. Crocodilians have sense organs in the skin that allow them to detect pressure waves underwater, and this probably helps them catch prey underwater.

American alligators grow to about 9 (maximum length for females) to 14 feet (maximum length for males). Females make nests from mud and vegetation, laying eggs at the top of this mound. She guards the nest until the babies hatch, at which time she carries them in her mouth to the water where the babies swim off. Alligators prefer swamps and marshes, lakesides and ponds, as well as rivers. Although usually rather shy and apt to swim away from humans, they are potentially dangerous animals that should not be approached closely. It is particularly risky to feed ‘gators in the wild, as they may become unafraid of people and may associate them with food, and be more likely to attack.

American crocodiles can grow very large, with the maximum male length about 16 feet. They can live in freshwater as well as brackish (partly salty) marshes and wetlands. How do you tell the difference between an alligator and a crocodile? Alligators have wider jaws, looking like a “U” from above, while crocodiles have more narrow jaws that look like a “V” from above. The alligator’s upper jaw is wide enough that the upper teeth overlap the lower ones, so that mostly only the upper teeth can be seen when the jaws are closed. The crocodile, on the other hand, has upper and lower jaws close to the same size so that both upper and lower teeth are visible. The large fourth tooth from the front, on the crocodile’s lower jaw, is visible over a groove in the upper jaw.

Identify Venomous Snakes!

Click to download a guide to identifying the venomous snakes of north Texas.