characteristics of Reptiles

Taxonomic Classification of Reptilia

  • Kingdom: Animalia

  • Phylum: Chordata

  • Class: Reptilia

  • Orders of Reptiles: The class Reptilia is divided into four distinct orders:
        * Order 1: Testudines: Includes turtles and tortoises.
        * Order 2: Squamata: Includes lizards and snakes.
        * Order 3: Crocodilia: Includes crocodiles, alligators, caimans, and gharials.
        * Order 4: Rynchocephalia: Often represented by the tuatara.

Principal Physiological and Physical Characteristics

  • Evolutionary Milestones: Reptiles represent the first group of creeping animals to live exclusively on land. They are primarily terrestrial animals.

  • Locomotion and Appendages:
        * Reptiles typically possess four limbs.
        * The limb structure is pentadactyl, meaning they have five digits on each limb.
        * The toes are equipped with claws to aid in terrestrial survival.

  • Thermoregulation:
        * Reptiles are cold-blooded, also known as ectothermic organisms.
        * They lack the physiological ability to internalize and control their own body temperature; instead, they rely on environmental heat sources.

  • Integumentary System (Skin and Exoskeleton):
        * The body is protected by an exoskeleton composed of horny scales, scutes, or bony plates.
        * These structural coverings serve a vital function in retaining internal moisture and preventing dehydration.
        * The skin is characterized as dry and non-glandular; glands are entirely absent from the skin of reptiles.
        * The body surface is covered by dry, bony scutes.

Craniofacial and Respiratory Features

  • Dental Variations: All turtles are notable for the absence of teeth. In their place, they possess a specialized beak and exceptionally strong biting jaws.

  • Respiratory System:
        * Respiration is primarily handled by the lungs.
        * The lungs are specialized with a large surface area to maximize oxygen exchange efficiency.

Circulatory and Excretory Systems

  • Cardiac Morphology:
        * In the majority of reptiles, the heart is divided into two auricles (atria).
        * The ventricle is divided into two chambers, but this division is incompletely formed.
        * Exception: Members of the order Crocodilia possess a fully formed quadruple-chambered heart (44 chambers).

  • Excretory System:
        * Reptiles possess metanephric kidneys.
        * Each kidney is functionally connected to the outside via a separate ureter.

Sensory Organs and the Nervous System

  • Auditory Organs: The primary sense organ for hearing is the tympanum, commonly known as the ear drum.

  • Olfactory Specialization: The Jacobson organ is a specialized sensory structure sensitive to odors, allowing the reptile to perceive smells from its environment.

  • Neurological Structure:
        * General reptiles possess 1212 pairs of cranial nerves.
        * Exception: Snakes are distinguished by having only 1010 pairs of cranial nerves.

Reproduction, Embryology, and Development

  • Fertilization and Oviposition:
        * Fertilization is strictly internal.
        * Reptiles lay their eggs on land.

  • Developmental Stages: Reptiles do not undergo any larval stages in their development.

  • Amniote Classification:
        * Reptiles are classified as amniotes because extra-embryonic membranes are present during the development of the embryo.
        * There are exactly four extra-embryonic membranes present:
            1. Amnion
            2. Chorion
            3. Allantois
            4. Yolk sac

Physiological Growth and Maintenance

  • Ecdysis: Also known as moulting, ecdysis is the process of shedding the old skin. This is a common biological occurrence across the reptile class.