Understanding the Skeleton of a Turtle


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A preserved turtle skeleton revealing how the plastron and carapace connect to the remainder of the turtle’s body to form a protective shell surrounding the entire body. skeletal components (upper) and limbs (lower) of a turtle. The turtle shell is an extremely complex defensive shield for all the vascular and urinary components of turtles (order Testudines). This defensive system also provides protection from irritants, predators and infections.

Although it may seem very difficult to imagine the immense size of a turtle shell, it is possible to examine one very carefully. Using a microscope, a vet can look at a piece of a shell under the microscope and see very clearly how well arranged the shell is. Even though a turtle skeleton can be seen with the naked eye, it is estimated that a healthy adult turtle has about 400 bones. It is estimated that the average turtle adult weighs in the range of sixteen to twenty pounds.

A relatively recent study by graduate student T. J. Martindale and his coworkers at the University of Texas found the largest example of a turtle eggshell from the same age of the Triassic period. This discovery of the eggshell supports the theory that the first sea turtles originated from the Triassic. At about twenty million years old this shell is the largest of its kind to be discovered. Furthermore, it is four times larger than the eggshell of the next oldest sea turtle.

The study was published in the March 2021 edition of the journal Paleo Biology. In addition to the spectacular fossilized eggshell this study also included two other relatively complete turtle skeletons. These consist of the anterior (or parrot-style) carapace, which is nearly complete, and the holotype or egg-type scute, which has a partial tail and ribs.

The most complete animal known to have evolved from the Triassic was an early ancestor of all modern turtles. Called the ecomorphous turtle because of its hard plastron (a hard, thick shell) and osteoid (an early ancestor of today’s turtles) scapulae, it possessed a flipper that would have been similar to the later alligator. Early elasmosaurians (earliest reptiles) were small to medium in size, and their limbs had a bony cover called a plastron. At the beginning of the Cretaceous period (about 65 million year ago) an advance toward terminal plastrons, or more thick plasters, began. New elements like horn and bone became incorporated into the plastron and this marked the first appearance of true turtles.

Over the past half million years since this first appearance of turtles, they have evolved into a wide variety of reptiles. Most are semi-aquatic and eat both fish and aquatic plants. But there are also terrestrial turtles and some that are strictly nocturnal. All are considered aquatic reptiles and are capable of moving about in the water, although they often stay in holes they construct as their only habitat.

One of the most complete fossils from pre-Cretaceous times is the so-called “stem-to Turtle fossil.” This relatively complete fossil is a relatively complete example of what theropods were commonly called, and includes both an anterior (or sternum) and a posterior (or belly) shell. It is thought that the relatively incomplete arrangement of the teeth (including the presence of a tooth bearing hooked claws and an additional tooth embedded in the back of the shell) may indicate that this animal used the stem as a swimming tube when walking on land.

The first vertebra in the series of ribs connecting the ribs of either side of the turtle body to the rib cage is called the pectoralis major. The other four ribs (the pectoralis minor, paraspostral, dorsal, and pelvic) link on the right side of the chest cavity (right side of the chest cavity is called the ectophyseal) to the two breast flaps, which in turn link the two sides of the chest cavity to the diaphragm, the abdominal wall, and the two sides of the thorax. This skeleton does not include the tail, legs, or tail claws. In order to better understand evolution and the development of life on earth we must be familiar with skeletal systems.

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