Reptile Biology: Adaptations, Anatomy, and Classification

Reptile Skin

Dry, thick skin covered with scales prevents moisture loss and protects against predators. Due to their specialized skin, reptiles are entirely dependent on lungs for gas exchange.

Reptile Skeleton

Legs are located under the body, not out to the side like in amphibians. This allows for better support and easier movement on land, increasing their chances of catching prey and avoiding predators. Claws on their feet allow for grasping.

Reptile Heart

Most reptiles have a three-chambered heart, but some (notably crocodilians) have a four-chambered heart. This separates oxygenated blood from deoxygenated blood, enabling more O2 to reach body tissues. This supports the higher level of energy use required by land animals.

Reptile Reproduction

Reptiles lay eggs on land, with no aquatic larval stage. The evolution of the amniotic egg freed early reptiles from dependence on water for reproduction.

Temperature Regulation

Similar to amphibians, reptiles are ectotherms. They cannot internally control their body temperature but have developed behaviors to respond to their environment.

Reptile Diet

• Turtles and Tortoises: Generally slow, most are herbivores or prey on worms or mollusks (snapping turtles are an exception).
• Lizards: Primarily eat insects (Galapagos marine iguanas and Komodo Dragons are exceptions).

Reptile Sense Organs

In addition to eyes and other obvious sense organs, reptiles have unique ways of sensing their environment. For example, some snakes can sense small changes in heat produced by other organisms.

Reptile Orders

Order Chelonia – Turtles and Tortoises

They have shells made of two parts: the carapace (dorsal) and the plastron (ventral). Vertebrae and ribs are fused, and muscles are attached to the inside of the carapace. Most shells are hard and bony, but some are tough and leathery.

Order Squamata – Snakes and Lizards

Lizards are found in many habitats in all but arctic regions of the world, possessing many adaptations that allow this (Fig. 31.7). They live on the ground, underground, in trees, and in water; some thrive in very hot, dry climates.

Order Crocodilia – Crocodiles and Alligators

This order includes the largest living reptiles. Crocodiles have long, skinny snouts, while alligators have short, broad snouts. Both possess powerful jaws and sharp teeth; many will catch prey and then pull it underwater to drown it.

Order Rhynchocephalia – Tuatara and Extinct Relatives

Tuatara is one of only two living species, found exclusively in New Zealand. Most of its close ancestors died out 100 million years ago. A number of characteristics differentiate it from lizards:

• Two rows of teeth on the top jaw, with the bottom row fitting between them.

Early Reptile Evolution

Early reptiles (cotylosaurs, Fig. 31.1 and 31.10) appeared in the Paleozoic Era and diversified into many lineages in the Mesozoic Era, including snake and lizard ancestors, turtles, crocodilian ancestors, birds, and dinosaurs.