vertebratesincluding

Vertebrates, including fishes, amphibians, reptiles, birds, and mammals, are a subphylum of chordates characterized by a vertebral column. They typically have an endoskeleton, a cranium, a closed circulatory system with a ventral heart, and complex organ systems. Their bodies exhibit bilateral symmetry and a high degree of regional specialization, allowing diverse lifestyles and habitats.

The vertebrate body plan supports a wide range of adaptations. Many have paired appendages, efficient respiratory mechanisms, and advanced nervous and sensory systems. Reproduction is varied, with fertilization usually internal in terrestrial species and external in most aquatic ones. Development can be direct or involve larval stages, as seen in many amphibians and some fishes.

Major groups include jawless fishes (such as lampreys and hagfishes), jawed fishes (cartilaginous and bony fishes), amphibians (frogs, salamanders, caecilians), reptiles (turtles, snakes, lizards, crocodilians, and birds), and mammals. Birds are a group within reptiles, having evolved from theropod dinosaurs and retaining distinctive features such as feathers, beaks, and an endothermic metabolism.

Ecologically, vertebrates occupy nearly every terrestrial and aquatic niche, from microscopic streams to vast oceans. They play central roles as predators, prey, herbivores, and scavengers, and they contribute to seed dispersal, pollination, and nutrient cycling. The vertebrate lineage arose in the early Paleozoic era and expanded through key innovations, including a vertebral column, jaws, limbs capable of land locomotion, and, in amniotes, eggs that tolerate dry environments.