Vertebrates, Mammals, Reptiles, and Birds: Characteristics

Vertebrates vs. Invertebrates

Vertebrates: are generally larger than invertebrates and possess a bony or cartilaginous internal skeleton. This skeleton includes a spine composed of bones or cartilages called vertebrae.

Invertebrates: lack a spine and internal skeleton. They exhibit either radial or bilateral symmetry, undergo metamorphosis to reach adulthood, and their bodies are formed by true tissues.

Mammals: Key Characteristics

Mammals are characterized by:

• The presence of hair on their bodies.
• The ability to regulate their body heat (homeothermy), making them warm-blooded animals.
• Internal fertilization and viviparous reproduction (live birth).
• Pulmonary respiration.
• Double-loop blood circulation with a heart divided into four chambers.
• A skeleton consisting of a skull and spine.
• A complex and developed nervous system.

Reptiles: Key Characteristics

Reptiles are characterized by:

• Thick skin protected by corneal scales.
• Reproduction that can be oviparous (egg-laying) or viviparous (live birth), with internal fertilization.
• Pulmonary respiration throughout their lives.
• Double and incomplete blood circulation with a heart divided into three chambers (two atria and one ventricle).
• A skeleton consisting of four extremities and an ossified skull and spine divided into five regions (cervical, thoracic, lumbar, sacral, and caudal).
• A nervous system consisting of 12 pairs of cranial nerves, similar to mammals.
• Rigid, often innate, behavioral patterns, especially related to reproduction.
• Adaptation to terrestrial life, often independent of aquatic environments.
• Dependence on the environment for temperature regulation; they are cold-blooded animals (poikilotherms).
• Amniotic eggs with a chorion covering the inner surface of the eggshell, involved in gas exchange, and a yolk sac that nourishes the embryo.

Birds: Key Characteristics

Birds are vertebrate homeotherms (constant body temperature) with pulmonary respiration. Their skin is covered in feathers, of which there are two types: contour feathers (covering the body and tail) and down feathers (more plush).

They possess a beak (picocornio), forelimbs modified into wings, rear limbs with clawed feet, and scales. Besides wings, they have other adaptations for flight, including:

• Hollow and lightweight bones.
• No bladder.
• Reproductive organs that decrease in size during the non-breeding season.
• Internal fertilization and oviparous reproduction (egg-laying). They incubate their eggs.
• A heart with four chambers (two atria and two ventricles).
• A digestive system with a crop, gizzard, stomach, and intestines.
• An air sac system to aid in ventilation during breathing.