Reptiles

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Reptiles are ectothermic animals—often called “cold-blooded”—and rely on external heat sources like the sun to regulate their body temperature.

Their scaly skin helps prevent them from drying out on land.

They breathe through lungs and have strong sense organs. For example, crocodiles rely on sharp vision, while turtles use their keen sense of smell, and snakes detect scents with their tongues.

Most reptiles reproduce by laying amniotic eggs with leathery or hard shells that can survive on land. While some lizards and snakes can also give birth to live young, highlighting the diversity of reproductive strategies among reptiles.

Reptiles are tetrapods—vertebrates that originally had four limbs—even though some, like snakes, have lost them through evolution.

Living reptiles are further classified into four main groups: squamates, such as snakes and lizards; crocodilians, including alligators and crocodiles; testudines, like turtles and tortoises; and sphenodonts, such as the tuatara.

Overview

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Reptiles

Reptiles are cold-blooded vertebrates that first appeared over 300 million years ago and were among the earliest animals fully adapted to life on land. Their scaly, waterproof skin and ability to lay amniotic eggs with protective shells allow them to reproduce without water, enabling survival in diverse habitats like deserts, forests, wetlands, and coastal areas. Modern reptiles include snakes, lizards, turtles, crocodiles, and the tuatara. Reptiles breathe through lungs and typically have a three-chambered heart, though crocodilians have four. Their skeletons and muscles support land movement, while species like sea turtles and crocodiles are also adapted for swimming. Reproduction involves internal fertilization, with most laying leathery eggs on land, while some give birth to live young. These features contribute to their evolutionary success in terrestrial environments.

Science and Engineering Practices (SEP): Developing and Using Models

Scientists use models to study reptilian adaptations, including their movement, body structures, and reproductive strategies. These models help explain how reptiles interact with their environments and how they have evolved over time.

Activity Ideas:

Compare Reptile Types – Create a chart comparing snakes, lizards, turtles, and crocodiles based on traits such as skin type, limbs, movement, and reproduction.
Amniotic Egg Model – Build a model to show the parts of an amniotic egg and how each component protects and nourishes the embryo.

Crosscutting Concept (CCC): Structure and Function

Reptiles exhibit specialized structures that serve vital functions for survival in diverse land environments.

Structure: Scaly, keratinized skin
Function: Reduces water loss and offers protection in dry habitats.
Structure: Amniotic egg with a leathery or hard shell
Function: Supports land-based reproduction by shielding the embryo from desiccation.
Structure: Snake’s unhinging jaw
Function: Allows ingestion of large prey, enabling dietary flexibility.
Structure: Turtle’s hard shell
Function: Acts as armor against predators.
Structure: Ectothermic physiology
Function: Saves energy by using external heat but limits cold-weather activity.
Structure: Strong limbs and flexible spine
Function: Support varied locomotion—crawling, swimming, slithering, or climbing.

Understanding these structure-function links helps explain how reptiles thrive in a range of terrestrial ecosystems.

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Transcript

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Ectothermic Physiology

Structure Function

Developing Using Models

Crosscutting Concept

Internal Fertilization

Terrestrial Adaptation