The Tortoise is a terrestrial turtle (lives on land). It is most identified by it's hard shell and retractable limbs. Like all reptiles, they are cold blooded, but tortoises have the ability to use their shell to obtain body heat. Most tortoises burrow into the ground to stay cool.  The mother tortoise builds a nest for her eggs, and leaves them to fend on their own. The hatchlings grow off of nutrients around them, and spread out to continue on their species.  Adult tortoises live in warm or hot climates, and have many predators. But despite all of these obstacles, the Testudinidae family continues to grow and survive. 
The most noticeable body part of the tortoise is it's shell. The shell is made of two parts. The top is called the carapace, and the bottom the plastron. Both sides of the shell are held together at the sides by the bridge. A type of Keratin called scutes make up large plates that cover several long bones that hold the shell together, and give it it's strength. Tortoises are able to retract their head and tail into their shell for protection. A Tortoises body can be from a few centimeters to a couple meters long. 
The shell grows along with the tortoise, and gets larger as layers of keratin grows from the plastron to expand it.  The female tortoise tends to be larger than the male. The males have a longer neck, and the females usually have longer claws. The main difference is that females have very short tales compared to the males.  Tortoises have very weak muscles in their back because their spine is rigid. But the muscles in their necks are very strong, and enable them to retract into their shells. The tortoise also has remarkably strong jaw muscles. Tortoises are cold blooded. Some tortoises have a lighter colored shell to attract less heat in very warm climates. They have fairly good eyesight, having eyes on the side of their heads. But they cannot see in very great detail. Their hearing ability is also very weak. This leaves their sense of smell. This is the tortoises greatest sense. They use smell for everything they do, from smelling for predators to finding a mate. 
Tortoise Shell and Heat Exchange
Tortoises are cold blooded, so in order for their organs to function they must find an external heat source. By facing their carapaces (their hard upper shell) toward the sun, or other heat sources, they can receive the heat their body cannot make (unlike warm blooded mammals who generate their own heat). The coloration of the tortoises shell is made to absorb heat. This can happened because of the tiny pores on the tortoises carapace that trap radiant heat. 
Just like in mammals, a tortoise's heart pumps blood to all the vital organs. Then it sends a sufficient amount of blood to underneath the carapace to warm it up. Finally it circulates (to move continuously or freely through an area) through the rest of the body. Their internal temperature must be between 25-35°c for a turtle's organs to function properly. 
Female tortoises lay around a dozen eggs at a time. They find a burrow or dig a hole for the eggs.  The mother will usually lay her eggs at night. Afterwards she will cover them in sand, leaves, or other materials. She then leaves the eggs to hatch on their own. Incubation time (the period before an egg hatches) for Tortoises is from 60 to 120 days. 
When the hatchlings are fully grown, they will use their egg tooth (a hard white tooth that is later lost) to break out of the shell. The hatchlings then crawl out of their nest and begin life on their own. The embryo from their eggs is eaten for nutrition during the first couple days, until they can eat solid food. Tortoises are amazing creatures that show God's unique design, with their special features, and how the mother's know how to make a nest for her young.  Tortoises are considered the longest-living animals. They can live over 150 years. Tortoises are amazing creatures that show God's unique design, with their special features, and the mother's ability to built a safe nest for her young. 
The first and most obvious reason tortoises impact the environment is from the burrows and nests they build for the young. The tortoise requires movable soil, and organic materials. When the Tortoises hatch they will need worms or insect larvae to survive. They have a strictly herbivorous diet.  Tortoises have many predators, from ravens to coyotes and dogs. Dog's commonly prey on adult tortoises, either in wild habitats of suburbs. Humans also have a large impact on tortoises. Our agriculture, roads, power lines, and any other land impact we have on the environment can effect them. 
Tortoises can live in many parts of the world, but the most common Tortoise, the Desert Tortoise, lives in hot climates in bush scrub habitats. The Desert Tortoise is able to obtain 140 degree weather because of it's ability to burrow underground. They spend 98% of their time underground. Desert Tortoises spend November to February in a dormant state (having normal physical functions slowed down for a period of time) for hibernation (a state of inactivity during winter months). The Desert Tortoise's most active time is in the spring when they search for food. During the hot season they store water inside their body, much like a camel. The Desert Tortoise is only one example, but all of family Testudinidae have a similar lifestyle.
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