selkärankaiseläimet

Selkärankaiseläimet constitute a subphylum within the phylum Chordata, characterized by the presence of a vertebral column, or backbone. This bony or cartilaginous structure encases and protects the spinal cord, which is a key feature distinguishing them from other chordates. Vertebrates are a highly diverse group, encompassing a vast array of species found in nearly every environment on Earth.

The subphylum is typically divided into five major classes: fish, amphibians, reptiles, birds, and mammals. Fish are aquatic vertebrates that breathe using gills and typically have fins for locomotion. Amphibians, such as frogs and salamanders, often exhibit a biphasic life cycle, spending part of their lives in water and part on land, and possess moist skin. Reptiles, like snakes, lizards, and turtles, are characterized by scaly skin and typically lay amniotic eggs on land. Birds are feathered, winged vertebrates, most of which are capable of flight, and are warm-blooded. Mammals are distinguished by the presence of mammary glands in females, fur or hair, and are warm-blooded.

Vertebrates exhibit a wide range of adaptations for survival, including complex sensory systems, highly developed nervous systems, and varied reproductive strategies. Their evolutionary history is extensive, with fossil evidence indicating their origins date back over 500 million years. The success and diversity of vertebrates underscore their significant role in Earth's ecosystems.