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General Information- Chelonians
Class Reptilia, Order Testudines

Snapping Turtle
Snapping Turtle
Chelydra serpentina
Bradford County, PA

Species
    Chelonians, or turtles, are characterized by one thing- the shell. This makes them instantly recognizable. There are nearly 600 species of turtle worldwide, but only 19 of these species can be found in our range. Five of these are collectively known as the "sea turtles" because of their complete use of and dependence on the open ocean.
    Besides the shell, turtles have four legs and a tail. The jaws are covered in a horny substance which makes a beak; there are no teeth. Turtles also possess an external ear structure known as the tympanum. The tympanum functions to amplify the audio signal before it reaches the brain. Turtles, like all reptiles, have dry skin covered in scales, but unlike the lizards and snakes, who shed their skin in one solid piece, the turtles constantly shed in small pieces. Thus, it is not unusual to find a turtle with flaking skin. This is a normal part of the shedding process.
    Some turtles are terrestrial, such as the Box Turtle (Terrapene c. carolina) and the Wood Turtle (Clemmys insculpta). Others are considered semi-aquatic. Examples of this are the Map Turtle (Graptemys geographica) and the common Painted Turtle (Chrysemys picta). Still others are fully aquatic and come to shore only to lay eggs. The before-mentioned sea turtles are the most stunning example of a fully aquatic lifestyle.
    The diet of most turtles is carnivorous. This is especially true of the aquatic and semi-aquatic species. Turtles have a horny beak but no teeth. The beak is specialized for tearing off bite sized pieces. Therefore turtles are not limited by the size of what they eat. Terrestrial turtles tend to be somewhat more omnivorous, eating a variety of vegetable material along with animal protein.

Terminology

Turtles, more so than any other taxon, have specialized structures that require special names. A few of these follow.


Basking
    If you spend a lot of time outdoors you have undoubtedly seen turtles stacked upon logs and other structures along the pond edges. Many hypotheses have been proposed for why turtles bask. It is widely believed that turtles lay in the sun for the primary reason of thermoregulation. For an animal that spends most of its time in the cold waters there must be some way for it to raise its body temperature. This is exactly what basking is believed to accomplish.
    Another hypothesis for the function of basking is removal of external parasites. Algae and leeches are major parasites of turtles and when the turtles bask, they dry these marine life forms enough that the algae dies and the leeches drop off to return to the water.
    Why several turtles chose to bask on the same structure while ignoring other structures is unknown. It is probably due to microhabitat. Microhabitat is the term used to describe all of the features of a small area. A favorable microhabitat includes the presence of sunlight, of nearby vegetation, and water quality. The interaction of several characteristics make a certain haul-out site appealing to turtles while others are ignored, for one reason or another.
    It should be noted that not all turtles bask. Several species are fully aquatic and seldom leave the water other than to lay eggs. These species include the Snapping Turtle (Chelydra serpentina), the Softshell Turtles (Apalone sp.), and the Mud and Musk Turtles (Family Kinosternidae). Other species, such as the Box Turtle (Terrapene carolina) and the Wood Turtle (Clemmys insculpta) are almost completely terrestrial, thus, although they do bask, it occurs less frequently and is less obvious. The few turtles that do bask often are those referred to as the semi-aquatic turtles. These include the Red-eared Slider (Trachemys scripta) and the Painted Turtle (Chrysemys picta).

Reproduction
    Reproduction in turtles is quite straight forward. Fertilization is internal and unlike the squamates the male turtle has a true penis. Breeding in most species occurs in the spring after the hibernation period. Most often mating takes place in the water, however Box Turtles are the exception to this rule. After mating the eggs develop inside of the females body until they are ready to be laid. All turtles lay eggs. Eggs of some species are covered in a hard, calciferous shell while those of other species are leathery and more reminiscent of a snake egg. Eggs may also be spherical or elliptical, depending on the species.
    Laying time is most often late spring, two to three months after mating. Sandy soils near water are most often chosen as deposition sites, but eggs will be laid anywhere where the soil is soft enough to permit digging. The female begins by digging several test holes. She first urinates on the soil to loosen it and allow easier digging. She then digs the pit with alternate movements of her hind legs. If the soil conditions are not right, the female will not deposit the eggs, but will fill the hole with the excavated soil and move to another position to begin again. These false nests or "test holes" also function in confusing potential predators by giving them several identical nests to chose from, only a small number of which contain eggs. Once a hole has been dug which the female finds to her liking, she deposits the eggs. Following this, she covers the eggs with the excavated soil, and compresses this with her shell, urinating on the nest to help pack it down. In good years it is not uncommon for females to "double clutch" or produce two sets of eggs. They may mate a second time, or they may use sperm that is stored inside of their body.
    The eggs remain in the ground for several months before they hatch. The young turtles slit the egg with a specialized structure called the "egg tooth." This structure is a hardened projection with the sole function of opening the egg. A few days after hatching the egg tooth falls off. The young turtle spends several days inside of the egg absorbing the rest of its yolk before crawling out of its shell and digging its way out of the ground. It is not uncommon for small turtles to be found with some of the yolk sac still attached.
    Young turtles of most species must then find the water. Much research has been done with sea turtles on this subject and the conclusion has been reached that they follow the reflection of the moon on the water's surface. Young from nests made near human population centers face the problem of artificial lighting. The young turtles follow the brightest light in the environment and most often this is human-made artificial lights. The young turtles are lured to highways and roadways to their deaths.
Research has shown that other young turtles have the ability to seek out and locate water sources, but exactly how they do it is uncertain at this time.

Wood Turtle
Wood Turtle
Clemmys insculpta
Tioga County, NY

Families
Turtles are classified in the Class Reptilia, Order Testudines. They are sometimes referred to as chelonians. There are 19 species and subspecies in our range representing 5 families.

Family Dermochelyidae- Leatherback

The only member of this family is the gigantic Leatherback, the largest turtle in the world. This family is characterized by front limbs modified into flippers and the lack of bony plates on the back. Instead, there are seven longitudinal ridges along the carapace. There are five similar ridges on the plastron. The distribution of this marine turtle is mainly tropical, but it migrates into cooler waters during the summer months.

Family Cheloniidae- Sea Turtles

Like the Leatherback these turtles have front limbs modified into flippers, but unlike the Leatherback they do have a hard shell made up of horny plates. They are marine in distribution and mainly tropical, but occur in the temperate region regularly in summer and rarely in winter. It is easy to place Sea Turtles into the group, but can be difficult to put into species because they are all simialar. Checking the differences in scalation is the most sure way to tell the species from one another. Unfortunately, often all one sees is a fleeting glimpse as the turtle disappears into the water. They mate in the water, but must come ashore to lay their eggs on sandy beaches. They lay many eggs, and many hatch, but few survive the trek to the water. Predators on the young include gulls, herons, raccoons, and even crabs. Once in the water they must still be on the lookout out for predators. Once the young turtles reach their juvenile sizes they have no predators other than man. Sea turtles are critically endangered because of hunting for meat and the eggs are collected as a delicacy and an aphrodisiac.

Family Chelydridae- Snapping Turtles

This small family consists of two species, the Common Snapping Turtle and the Alligator Snapping Turtle (Macroclemys temmincki) of the south. They are large turtles with a reduced plastron and a large head equipped with powerful hooked jaws. They are primitive looking and omnivorous, although with a definite preference toward carnivory. Both species are often used for food, especially in the southern states. Overhunting has decreased population sizes of the Alligator Snapper, but the Common Snapper is holding its own. They are erroneously thought by fishermen and waterfowl hunters to be harmful to fish and duck populations, but these outdoorsmen take more fish and ducks in a season than a snapping turtle does in a lifetime.

Family Kinosternidae- Musk and Mud Turtles

Members of this family are small, oval shaped, and have a highly domed carapace. Mud turtles have a single hinge on the plastron, while musk turtles have two. This hinge allows the turtle to close up, although not as tightly as the familiar box turtle. The plastron in most is somewhat reduced and in the Common Musk Turtle there are patches of skin between the plastral scutes. There is sexual dimorphism in this group. Females have very short tails while the tail of male turtles extends past the edge of the carapace. These turtles are highly aquatic and are bottom dwellers. They seldom leave the water other than to lay eggs and they bask at the surface of the water with the top of the carapace sticking above the surface. The Kinosternidae possess two pairs of musk glands located along the margins of the bridge and lend credence to the names "Musk Turtle" and "Stinkpot".

Family Emydidae- Pond Turtles

The pond turtles are the most successful family of turtles in the world with over 80 species known. They are extremely successful in the east and the south. In our range they comprise over 40 percent of the number of species of turtles and much more than that in the number of individuals. These are the common turtles seen basking along pond edges in the spring and most are semiaquatic. A few are terrestrial. This family is characterized by flattened hind feet which are webbed and a well developed plastron. With the exception of the Box Turtle the carapace is flattened with little doming.

Family Trionychidae- Softshell Turtles

Softshell turtles are instantly recognizable because of one feature. They have no hard plates in the shell. Instead the shell is leathery and freely bends at the edges. The outline of the carapace is circular in shape and because of the lack of scutes the outline of the ribs sometimes shows through. Softshells are aquatic, but do bask along the shoreline edges. They are wary and very fast on land.  Softshells often sit in mud in the shallow water along the river edges with only the eyes and snout exposed. From here they only need reach up with their long neck to reach the surface and breath. Be careful when handling softshells because they possess sharp claws and strong jaws and it can be quite difficult to keep a firm grip.

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