Creatures of Scale (Grades 2-3)
Students learn about snakes, lizards, turtles, and tortoises from their evolution to their morphological characteristics and unique behaviors.
|Introduction||Ask students if they can think of a very old reptile (dinosaur). Back 200 million years ago was the age of the great ruling reptiles-the dinosaurs. However, 65 to 85 million years ago they disappeared. Why, scientists do not know. It may have been because of a meteor hitting the Earth. Those reptiles that did survive are the reptiles we know today.|
were the first totally terrestrial or land dwelling animal. They
could survive completely on land because of two very important characteristics:
1. Dry, scaly skin almost free of glands. The scales on these reptiles are made of keratin (hardened skin). The same material your fingernails are made of.
2. Shelled egg. The leathery or hard shell completely encloses and protects the developing baby. So now, reptiles can lay their eggs on land.
|Other characteristics that all
reptiles have are the following:
1. Internal skeleton made out of bone
4. Ectotherms - cold blooded- that means their internal body temperature changes with the outside environmental temperature.
|Turtles and Tortoises||Ask the students if they know the difference between a turtle and a tortoise. A tortoise lives on the land and the turtle lives in the water. There are clues to tell you which of the two is the turtle and which is the tortoise. The turtle has webbed feet for swimming in the water and the tortoise has claws for walking on land and burrowing into the dirt. Also the turtle is a meat eater (fish, meat) and the tortoise is a vegetarian (carrots, squash, and spinach). Explain to the students that the Desert Tortoise is endangered. Endangered means not very many are left in the wild.|
|Ask the students why they think a turtle needs a shell (protection).|
|Snakes||These are limbless reptiles. Snakes move by pushing off of surface bumps and grooves, moving in a s-shaped pattern.|
|One unique characteristic of snakes that other reptiles don't have is floating jaws. Snakes are known for their ability to eat animals several times wider than themselves. This is because their jaws and the bones in their skull are only loosely connected. Therefore, they can open their mouths extraordinarily wide. Snakes eat their food whole, in one big swallow. They do not chew.|
three ways snakes can capture
|Snakes actually have poor vision, but they can "taste" the environment around them. A snake keeps sticking its tongue in and out to taste the air around him. Each time the tongue comes out it picks up a sample of what's in the air (chemicals, dust) and brings it into the roof of the mouth where the sample is analyzed and the information sent to the brain.|
|All snakes periodically shed their scales anywhere from once to eight or ten times a year to accommodate their growth. The skin is generally shed in one piece, inside out, starting at the tip of the mouth, over the eye caps, to the tip of the tail.|
|Lizards||There are four types of lizards: Geckos, Iguanas, Skinks, and Chameleons. Lizards all have tails, which are extremely important. Some lizards use their tail for balance when moving very fast. Some lizards use their tails for protection. Their tails are spiny and they can whip it around at very high speeds. In geckos and Gila monsters, the tail is a reservoir where fats are stored for later use when food is scarce.|
|A lizard sheds its tail as an escape tactic. Where predators are rare, this drastic method of defense is less likely to be used. It is also less common among lizards that have other means of defense, such as thick armor or powerful teeth and claws.|
|Lizards are primarily vegetarians, but will eat insects and eggs.|
|How reptiles see||A reptile’s vision depends on the position of its eyes. A reptile with monocular vision has eyes on either side of the head. The area that one eye can see does not overlap the area the other eye can see. Land Tortoises, Crocodiles, and many lizards have monocular vision.|
|A reptile with binocular vision has both eyes facing forward. The area that each eye can see overlaps. Reptiles with binocular vision, like the snapping turtle, focus both eyes on their prey and can accurately judge its distance.|
|Not all reptiles see their surroundings in the same ways. The position of the eyes, the shape of the pupils, and the number and type of light-sensitive cells determine the range, depth, and color of a reptiles view. Some snakes can even "see" an image of warm-blooded prey by detecting the heat that the animal gives off.|
|Putting it all Together||Students must pick one reptile and complete a reptile worksheet (Reptile Report). After completion of the worksheet, students may draw their reptile on the back of the page.|
|1. This reptile lives...|
|2. This reptile moves by ...|
|3. This reptile eats ...|
|4. It gets its food by ...|
|5. The color of this reptile is ...|
|6. This reptile protects itself by ...|
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