Answered by Alana Jensen, Environmental Educator, INL ESER Program
Turtles and tortoises are the only reptiles with tough, bony shells. The shell has an outer layer of scutes made of hornlike material called keratin and an inner layer of bony plates.
There are two parts to the shell of a turtle: the upper portion is called the carapace and the bottom half is called the plastron. Both shells are actually made of many fused bones. The carapace is the fusion of about 50 bones – the ribs and vertebrae. The plastron is the fusion of bones including the clavicles (collar bones), bones between the clavicles, and portions of the ribs. A bony bridge joins the carapace and the plastron along the side of the turtle. Some turtles have a moveable joint, usually in the plastron, which acts as a hinge and allows the turtle to pull the carapace and plastron together tightly when the turtle retracts its body into the shell. Shells have a blood and nerve supply, so bleeding and pain can result if the shell is injured.
The shells are covered with a layer of keratin (the same type of material that makes up our fingernails or horses’ hooves). The keratin is arranged in patches called scutes. The carapace usually has 38 scutes, and the plastron, twelve to fourteen. The scutes are staggered over the bony plates, which helps give the shell more rigidity.
Some aquatic turtles, such as soft-shelled and sea turtles, may have fewer bones in their carapaces, and the scutes are replaced by leathery skin.
As a shell grows, the number of scutes generally does not change, but their size does. In some turtles, old scutes are shed and replaced by larger, new ones. In other species, including box turtles, tortoises, and wood turtles, scutes enlarge in diameter as new keratin is laid down. The “growth rings” in scutes have been used be some experts to help determine the age of a turtle.
Turtle, Tortoise or Terrapin?
Turtles, tortoises and terrapins are closely related reptiles of the order Testudines
Turtle is often used to refer to sea turtles who spend most of their lives in the water. Because of this, their feet are normally webbed or flipper-shaped. This helps them swim fast and strong. Also, their body is more streamlined than their tortoise and terrapin relatives.
Terrapin are turtles spend their life both on land and in water. They always live near water, along rivers, ponds and lakes. They can have webbed feet for swimming and claws for climbing. They are also usually small and have a hard-shell that’s shaped somewhere between a turtle’s streamlined one and a tortoise’s rounded dome shaped one.
Tortoise live only on land. They have a high-domed shell to protect them from predators and help them keep cool. Instead, their feet are rounded and more stumpy, which allows them to walk on land and to dig burrows.
Keratin is a family of proteins that are among the most important and versatile compounds ever produced in nature. They are what make up hair in animals, as well as horns, nails, hooves, shells, beaks, and feathers.
Keratin proteins make up our hair, nails and skin. Keratin gives these body parts strength for protection. Keratin can also help injured cells to heal and grow. It is what makes skin waterproof.
As keratin cells naturally push upward through the skin, they die and then harden, turning into your hair or nails. Known as keratinization, this process is what makes hair and nails grow. Hair grows an average of 3 inches a year, whereas nails usually grow about 1 1/2 inches a year.
Materials: permanent marker, ruler
- Make a small mark near the center of your nail with a permanent marker.
- Measure the distance in mm from this mark to the base of your nail. This point will be your reference point for each measurement.
- Measure the distance every other day. Refresh the mark as need during the course of the activity. How much did your finger nail grow in a week? In a month?