Kranialliset

Kranialliset (Craniata) are a clade within the phylum Chordata defined by the presence of a skull, or cranium, that protects the brain and sensory organs. The group includes hagfishes (Myxini) and all vertebrates, such as lampreys, sharks, bony fishes, amphibians, reptiles, birds, and mammals. By contrast, other chordate lineages such as tunicates and cephalochordates lack a skull.

Typical craniates have a protective neurocranium, a more complex nervous system, pharyngeal arches, and an internal skeleton made of cartilage or bone. A vertebral column is common among craniates, but hagfishes possess a cranium without a true backbone.

Evolution and classification: Craniata is thought to have originated in the early Cambrian period, with the earliest fossils of craniates dating to about 520–500 million years ago. The major lineages are Myxini (hagfishes) and Vertebrata, which includes both jawless and jawed vertebrates. Jawed vertebrates (gnathostomes) later diversified widely.

Diversity and ecology: Craniates inhabit marine and freshwater environments worldwide, occupying roles from scavengers and filter feeders to active predators. They range from small species to large vertebrates such as whales and sharks.

In biology, craniates are central to studies of vertebrate evolution, development and comparative anatomy, illustrating how the skull and related structures evolved to support a wider range of lifestyles.